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Chapter 11: Study of Animal Type – Cockroach

Coal is nothing but the crushed remains of ancient forests. When geologists split open blocks of coal-bearing rock from the Carboniferous period — roughly 300 million years ago — they keep finding the same thing pressed into the stone: thin, finely veined insect wings, oval and leathery, so much like the forewing of a cockroach that palaeontologists began calling that stretch of Earth’s history the “age of cockroaches.”

Those ancient insects were not identical to the cockroach in your kitchen, but the body plan was already there: a flattened body, long feelers, tough plates over the back, wings folded flat. Whole continents have drifted, dinosaurs have come and gone, and that design is still running around behind the refrigerator.

That is exactly why biologists chose the cockroach as a “type study.” Instead of dissecting thousands of insects, we study one common, easily available insect in full detail — Periplaneta americana — and use it to understand how the entire class Insecta is built. Its digestive tube, its open blood system, its air tubes, its nerve cord: each one is a working model of an arthropod body.

In this chapter, you will take that model apart, organ by organ.

Diagram

Fig. 11.0 – Opening illustration: a fossil cockroach-like forewing preserved in dark Carboniferous rock on the left, and a living Periplaneta americana in the same posture on the right, with a dashed arrow labelled “≈300 million years” joining them

NoteCuriosity Corner

Q1. Why do you almost always spot cockroaches at night, in damp and dark corners, and never sunning themselves on an open floor? Q2. A cockroach’s blood is colourless and carries no oxygen at all — so how does oxygen still reach the muscles deep inside its body? Q3. A cockroach already has hard jaws outside its mouth. Why does it then need a set of six teeth inside its food canal as well? Q4. The outer covering of a cockroach is hard and non-living. How, then, does a young cockroach manage to grow bigger? Q5. If you were handed two cockroaches, how could you tell the male from the female without dissecting either of them?

This chapter will answer each of these questions as you work through it.

11.1 Habit and Habitat

  1. How many different types of animals live around us?
  2. Could one person possibly study every one of those animals in detail?
  3. Which phylum is the most diverse and the most populous?

Cockroaches are omnipresent — they are present everywhere, all over the world. Very few land animals have managed to spread this widely.

Where It Lives

It prefers damp and moist places, and it lives in crevices — the narrow cracks and gaps in walls, floors, drains and old furniture. A crevice suits it well because it is dark, it holds moisture, and its walls press against the insect’s flat body from both sides.

How It Feeds and Moves

The cockroach is omnivorous, nocturnal and cursorial. Omnivorous means it feeds on both plant and animal material, so almost anything organic can serve as food. Nocturnal means it is active at night and stays hidden by day. Cursorial means its body is adapted for running rather than for flight — when disturbed, it escapes on its legs, not on its wings.

Omnipresent vs Omnivorous Omnipresent describes where the animal is found — everywhere in the world. Omnivorous describes what it eats — both plant and animal matter. The two words look alike but answer completely different questions.

Q. If a cockroach has two pairs of wings, why is it called cursorial rather than a flier?

A. Because running, not flying, is its main way of moving and escaping. Its flight is short and clumsy, while its legs can carry it into a crevice in a fraction of a second. A term like “cursorial” describes the animal’s usual mode of locomotion, not everything it is capable of.

Common Indian Species

Periplaneta americana, Blatta orientalis and Blatta germanica are the three common species of cockroach found in India. Of these, Periplaneta americana is the species used for the detailed type study in this chapter.

The three species do not all turn up in the same place. Periplaneta americana is the large, reddish-brown one usually seen coming up from sewers and drains; Blatta orientalis favours cool, damp corners such as basements and drain surrounds; Blatta germanica is much smaller and is the one that hides inside kitchen cupboards and behind appliances. Knowing which species is present tells a pest-control worker where to search for the nest — a good example of how habit and habitat data are used in practice.

Q1. Why do you almost always spot cockroaches at night, in damp and dark corners, and never sunning themselves on an open floor?

A. Because the cockroach is nocturnal and prefers damp, dark crevices. An open, dry, lit floor offers it no moisture, no shelter and no escape route, and leaves it exposed to predators. Being cursorial, the moment light falls on it, it runs straight back to the nearest crack.

11.2 Systematic Position

The systematic position of an animal is simply its address in the system of classification. You begin with the largest, broadest group and move step by step to the narrowest one, and at every step the group becomes smaller while the animals inside it become more alike. The full path for our cockroach is set out in FC 11.1.

Flowchart

FC 11.1 – Systematic position of the cockroach, broadest group first: Kingdom Animalia (cell wall absent, heterotrophic nutrition) → Phylum Arthropoda (jointed appendages, segmented body, chitinous exoskeleton) → Class Insecta (two pairs of wings, three pairs of walking legs) → Genus Periplaneta (nocturnal, straight wings) → Species americana (origin is in Continent of America)

Reading Each Level

Kingdom : Animalia — cell wall absent, heterotrophic nutrition. Without a rigid cell wall the cells can change shape, which is what makes muscle and movement possible; heterotrophic means the animal cannot make its own food and must take it in ready-made.

Phylum : Arthropoda — jointed appendages are present, the body is segmented, and the exoskeleton is chitinous. The name itself says it: arthron means joint and podos means foot. Jointed legs are the reason a hard-cased animal can still bend and run.

Class : Insecta — two pairs of wings and three pairs of walking legs are present. This “six legs” rule is the quickest test for an insect.

Genus : Periplaneta — nocturnal, with straight wings.

Species : americana — origin is in the Continent of America.

The Two-Word Name

Putting the last two levels together gives the binomial name Periplaneta americana. The genus name is written first and begins with a capital letter, the species name follows in small letters, and both are printed in italics. Between Class and Genus the complete hierarchy also has the levels Order and Family; this chapter simply lists the levels needed to place the cockroach.

the order of taxonomic ranks King Philip Came Over For Good Soup — Kingdom, Phylum, Class, Order, Family, Genus, Species. Always recite it from the broadest group down to the narrowest.

Phylum Arthropoda vs Class Insecta Every insect is an arthropod, but not every arthropod is an insect. Arthropoda is the wider group and includes spiders, prawns and centipedes as well; Insecta is one class inside it, marked out by three pairs of walking legs and two pairs of wings.

Q. Why bother with a Latin two-word name when “cockroach” is easier to say?

A. Because “cockroach” is not precise. It is used loosely for thousands of different species, and every language has its own word for them. Periplaneta americana points to exactly one species, and it means the same thing to a scientist in Jaipur, Tokyo or Nairobi.

The habit of giving each organism a two-word Latin name was established by the Swedish naturalist Carl Linnaeus in the middle of the eighteenth century. Before him, a species was described by a long descriptive Latin phrase that different naturalists wrote differently. Linnaeus replaced these with a fixed genus-plus-species pair, and arranged organisms in nested ranks — the same ladder you have just used for the cockroach.

Laboratories across the world use the cockroach as a research animal. Because every one of them writes Periplaneta americana, a result obtained in one laboratory can be compared directly with a result from another. Had they all written only “cockroach,” nobody could be sure the same animal had been studied.

  1. Why do insects need to moult?
  2. What is the difference between a simple eye and a compound eye?

11.3 External Morphology

External morphology means everything you can study about an animal’s body from the outside — its shape, its covering, the regions it is divided into, and the appendages attached to each region. For the cockroach this outside view is unusually informative, because almost every external part is directly linked to how it feeds, hides, breathes or moves.

Shape and Size

The body of the cockroach is elongated, bilaterally symmetrical and dorso-ventrally flattened. Bilateral symmetry means a single cut down the middle from head to tail would give two mirror-image halves. Dorso-ventrally flattened means the body is pressed down from top to bottom, so it is broad but very thin from back to belly.

That flatness is not accidental. A thin body slides into narrow cracks in walls, under skirting boards and behind cupboards — exactly the crevices the animal prefers to live in.

dorso-ventrally flattened body Body pressed thin from top to bottom → the animal can squeeze into a crack only a few millimetres wide → it stays hidden from predators, keeps contact with moist surfaces on both sides, and reduces water loss.

Cockroaches are triploblastic, eucoelomate and truly segmented animals. Triploblastic means the embryo develops three germ layers — ectoderm, mesoderm and endoderm — from which all tissues arise. Eucoelomate means it possesses a true body cavity lined by tissue of mesodermal origin. Truly segmented means the body is built as a repeating series of similar units, or segments.

The body cavity of the cockroach is called the haemocoel, and it is filled with haemolymph, the body fluid of the insect. You will study the haemocoel in detail in the next section.

Diagram

Fig. 11.1 – Dorsal view of Periplaneta americana, labelled: head, filiform antennae, compound eye, pronotum, mesothorax, metathorax, prothoracic leg, mesothoracic leg, metathoracic leg, tegmina, hind wing, abdomen, anal cerci

The whole animal, seen from above, is shown in Fig. 11.1, and the same animal seen from below in Fig. 11.2. Compare the two carefully: the wings and the plates of the back dominate the dorsal view, while the legs, mouth parts and ventral plates dominate the ventral view.

Diagram

Fig. 11.2 – Ventral view of Periplaneta americana, labelled: head, antenna, compound eye, prothorax, mesothorax, fore leg, middle leg, hind leg, wing, abdomen, anal cercus

Coloration

The cockroach is glistening brown or red brown in colour. This dull, dark shade blends with wood, soil and the inside of drains, so a resting cockroach is hard to see against the surfaces it lives on.

Exoskeleton

The body of the cockroach is protected by a hard, waxy, tough, non-living exoskeleton. “Non-living” is an important word here: once formed, this covering contains no living cells, cannot repair itself and cannot grow.

The exoskeleton is formed by a nitrogenous polysaccharide called chitin. Chitin provides strength, elasticity and surface area for the attachment of muscles. Notice that all three are needed together — strength alone would make a brittle shell, and elasticity alone would make a covering too floppy to protect anything.

NoteDefinition

The exoskeleton is the hard, waxy, tough, non-living outer covering of the cockroach, formed of the nitrogenous polysaccharide chitin, which gives strength, elasticity and a surface for muscle attachment.

Because the exoskeleton is on the outside, the muscles must be attached to its inner surface and pull from within — the opposite of our own arrangement, where muscles wrap around an internal skeleton.

waxy exoskeleton Outer layer waxy and water-repellent → water cannot escape easily through the body surface → the insect survives in dry cupboards and can stay away from water for long periods.

Each body segment of the cockroach is covered by four chitinous plates, called sclerites. These are the dorsal tergum, the ventral sternum and two lateral pleurons — one on each side. Together they wrap a segment like a small four-piece box.

Tergum vs Sternum vs Pleuron Tergum is the plate on the dorsal (upper) side, sternum is the plate on the ventral (lower) side, and the two pleurons are the lateral (side) plates. All three are sclerites of the same segment — only their position differs.

Q4. The outer covering of a cockroach is hard and non-living. How, then, does a young cockroach manage to grow bigger?

A. It cannot stretch the old covering, because chitin is non-living and cannot grow. So the insect periodically sheds the entire exoskeleton — a process called moulting — and expands quickly before the newly secreted covering hardens. Growth in an insect therefore happens in jumps, at each moult, rather than continuously as in us.

Division of the Body

The body is divided into three regions: head, thorax and abdomen. This grouping of segments into three functional regions is a defining feature of insects, and each region has taken over a different job — sensing and feeding, locomotion, and the housing of the viscera.

Flowchart

FC 11.2 – Division of the cockroach’s body: Body → Head (6 fused segments; antennae, compound eyes, mouth parts) → Thorax (prothorax → mesothorax → metathorax; 3 pairs of legs, 2 pairs of wings) → Abdomen (10 segments; anal cerci, anal style in male)

The head is attached at right angles to the thorax by a thin, narrow, movable neck, also called the cervix. Because the neck is narrow and flexible, the head can be swung freely without the rest of the body moving.

The Head

The head is formed by the fusion of six segments. It is triangular or ovate in shape and, thanks to the flexible neck, it is highly mobile. It bears a pair of long antennae, a pair of compound eyes, and mouth parts adapted for chewing and biting of food. These structures are shown in Fig. 11.3.

Diagram

Fig. 11.3 – Lateral view of the head of cockroach, labelled: ocellar spot, compound eye, antenna, labrum, mandible, maxilla, labium

the head Zoom out: the head is one of the three regions of the whole body. Zoom in: it is itself six segments fused into one rigid capsule, and each of the appendages on it — antenna, mandible, maxilla, labium — is a modified limb of one of those original segments.

Antennae

The antennae are also called feelers. They are filamentous, long, segmented structures that can be moved in all directions. Being segmented is what allows a long antenna to sweep and curve instead of standing stiff.

They are lodged in membranous pits called antennal sockets. The soft membrane at the base is what permits movement in every direction.

Antennae are tactile (touch) as well as olfactory (smell) organs, and are useful in locating the food material in the vicinity. A cockroach walking in complete darkness therefore “sees” its surroundings through constant sweeping of the antennae.

Fenestrae

Fenestrae are also called ocellar spots. They are situated at the base of each antenna and appear as white spots.

Antennae vs Fenestrae The antennae are long, movable, segmented feelers used for touch and smell. The fenestrae are only small white spots (ocellar spots) at the base of each antenna — they are not movable and not appendages at all.

Compound Eyes

The compound eyes are paired, dark, kidney shaped structures placed on the lateral sides of the head. Their position on the sides, rather than the front, gives the insect a very wide field of view.

Each compound eye is made up of a large number of ommatidia (singular: ommatidium). Ommatidia are the structural and functional units of the compound eye, and each one forms an image of a very small part of the visual field.

Collectively, the compound eye produces a mosaic image — a single picture assembled from thousands of tiny separate pieces, rather like a photograph made of tiles.

NoteDefinition

An ommatidium is the structural and functional unit of a compound eye; each ommatidium forms an image of a very small part of the visual field, and all of them together produce a mosaic image.

Compound eyes are present in the cockroach, situated on the dorsal surface of the head. Each eye consists of about 2000 hexagonal ommatidia (singular: ommatidium). Each ommatidium is like a simple eye, forming an image independently, so with the help of several ommatidia a cockroach receives several images of an object. The compound eye gives mosaic or hazy vision, but the animal is able to detect even the slightest movement of an object. This kind of vision has more sensitivity but less resolution.

Simple eye vs Compound eye A simple eye has one lens and forms one image of the whole field. A compound eye has thousands of units, each forming an image of a tiny part of the field, and the brain combines them into one mosaic image — poorer in detail, but extremely quick to notice movement.

This is why a cockroach is so difficult to swat. Your hand crosses the boundary between one ommatidium’s field and the next many times as it descends, and each crossing is registered as a change. Movement, rather than fine detail, is what this eye is built to detect — and the animal is running before your hand arrives.

Mouth Parts

In front of the mouth the cockroach has a pre-oral cavity, in which food is received before it is actually swallowed. This cavity is bounded by chewing and biting type of mouth parts.

The mouth parts are movable, segmented appendages which assist in ingestion of food. Because they are separate movable pieces, each one can specialise in a different job — holding, cutting, tasting or pushing. They are shown in Fig. 11.4.

Diagram

Fig. 11.4 – Mouth parts of cockroach shown separately, labelled: labrum, mandible (with grinding region and incising region), maxilla (both), hypopharynx, labium

The mouth parts of the cockroach comprise the following.

i. Labrum (Upper lip): It is a single flap-like movable part which covers the mouth from the upper side. It forms the anterior wall of the pre-oral cavity and is useful in holding the food during feeding.

ii. Mandibles (True jaws): These are two dark, hard, chitinous structures with serrated median margins. They are present on either side, behind the labrum. They perform coordinated side-wise movements to cut and crush the food. This movement is effected with the help of adductor and abductor muscles — the adductor pulls a mandible inward towards the middle, and the abductor pulls it outward, so the pair works like a horizontal scissor rather than an up-and-down jaw.

iii. Maxillae (Accessory jaws): These are also called the first pair of maxillae. They are situated on either side of the mouth, behind the mandibles. Each maxilla consists of sclerites like cardo, stipes, galea, lacinia and maxillary palps. The maxillary palps act as tactile organs. The maxillae hold food and help the mandibles for mastication. Maxillae are also used for cleaning the antennae and front legs — grooming matters, because dirt on an antenna would blunt the insect’s sense of smell and touch.

iv. Labium (Lower lip): It is also called the second maxilla. It covers the pre-oral cavity from the ventral side and is firmly attached to the posterior part of the head. It has labial palps, which are three jointed and sensory in function. The labium is useful in pushing the chewed food into the pre-oral cavity, and it also prevents the loss of food falling from the mandibles during chewing.

v. Hypopharynx (Tongue): In front of the labium and between the first maxillae, there is a somewhat cylindrical single structure called the hypopharynx or lingua. A salivary duct opens at the base of this structure. The lingua bears comb-like plates called super-lingua on either side. It is useful in the process of feeding and in mixing of saliva with food.

the five mouth parts in order from front to back Labrum → Mandibles → Maxillae → Hypopharynx → Labium: “Little Men Make Hard Lunches.” The upper lip is in front, the lower lip is at the back, and the working parts lie in between.

a crumb of bread being taken in by a cockroach 1. The sweeping antennae detect the smell of the crumb and locate it in the vicinity. 2. The maxillary palps and labial palps touch and taste it, checking that it is edible. 3. The labrum, the flap-like upper lip, holds the crumb against the front of the pre-oral cavity. 4. The mandibles swing side-wise, their serrated margins cutting and crushing the crumb. 5. The maxillae grip the pieces and feed them back to the mandibles for further mastication. 6. Saliva flows from the duct at the base of the hypopharynx and is mixed into the crushed food. 7. The labium, from below and behind, pushes the moist food forward and stops any of it falling out. 8. The food, now soft and mixed with saliva, lies in the pre-oral cavity, ready to enter the mouth.

Q. Why does the cockroach need a pre-oral cavity at all, when the food could go straight into the mouth?

A. Because chewing has to happen somewhere. The pre-oral cavity is a working chamber outside the mouth in which food is held, cut, crushed and mixed with saliva. Only after that treatment is it soft enough to be swallowed — a hard, dry crumb entering the narrow food canal directly would simply block it.

The Thorax

The thorax is three segmented. The anterior segment is the prothorax, the middle one is the mesothorax and the posterior one is the metathorax. In Fig. 11.1 the large plate covering the prothorax, the pronotum, is the shield-like structure that partly hides the head from above.

The thorax bears three pairs of walking legs ventrally, one pair attached to each of the three segments, and two pairs of wings dorsally, attached to the mesothoracic and metathoracic segments. The thorax is therefore the locomotory region of the body — every organ of movement is anchored to it.

which thoracic segment carries what All three segments — prothorax, mesothorax and metathorax — carry one pair of legs each. But only the mesothorax and the metathorax carry wings; the prothorax has none.

The Legs

Three pairs of walking legs are present on the ventral side. Each leg has five podomeres, namely coxa, trochanter, femur, tibia and tarsus, joined end to end from the body outwards. The structure of a single leg is shown in Fig. 11.5, and the order of its parts in FC 11.3.

Diagram

Fig. 11.5 – Leg of cockroach, labelled from base to tip: coxa, trochanter, femur, tibia, tarsus

Flowchart

FC 11.3 – Parts of a cockroach leg from body outwards: coxa → trochanter → femur → tibia → tarsus (5 tarsomeres) → last tarsomere bears pair of claws + arolium

The tarsus is the last segment and is itself made up of five movable segments, or tarsomeres. The last tarsomere bears a pair of claws and a cushion-like arolium, which are helpful in clinging.

claws and arolium of the last tarsomere Sharp claws hook into rough surfaces → grip on wood, brick and soil; soft cushion-like arolium presses flat against smooth surfaces → grip on glass and polished tile → together they let the cockroach cling and run up almost any vertical surface.

the five podomeres of a leg Coxa, Trochanter, Femur, Tibia, Tarsus — “Cats Try Fresh Tuna Today.” Recite them from the body outwards, never the other way round.

The Wings

Two pairs of wings, the forewings and the hindwings, are present on the dorsal side. The forewings are the first pair — dark, opaque, thick and leathery wings, which are protective in function. In Fig. 11.1 they are labelled tegmina.

The hindwings are thin, broad, membranous, delicate and transparent. These are attached to the tergum of the metathorax. They are helpful in flight, and hence are also called the true wings.

Forewings vs Hindwings | Feature | Forewings (tegmina) | Hindwings | |—|—|—| | Position | First pair, dorsal | Second pair, dorsal | | Attached to | Mesothorax | Tergum of metathorax | | Texture | Dark, opaque, thick, leathery | Thin, broad, membranous, delicate, transparent | | Main function | Protective | Helpful in flight | | Also called | — | True wings |

Q. If only the hindwings are used in flight, why keep the heavy forewings at all?

A. Because at rest the delicate hindwings must be folded away and protected. The tough leathery forewings lie over them like a lid, shielding them from damage while the insect squeezes through crevices. The cockroach spends far more time running and hiding than flying, so protection matters more than lightness.

Spiracles

Spiracles are a series of slit-like openings present on either side of the body. In all, there are ten pairs — two on the thorax and eight on the abdomen.

The spiracles let the air into and out of the tubes called trachea. They are the external openings of the respiratory system, which you will study in Section 11.7.

The Abdomen

The abdomen is elongated and made up of ten segments. Each segment has a dorsal tergum and a ventral sternum.

Laterally, the tergum is jointed to the sternum by a soft cuticle called pleura. Because this joining cuticle is soft rather than hard, the abdomen can swell and shrink — which matters when a female is carrying developing eggs.

The posterior segments are telescoped in, meaning they slide partly inside one another like the tubes of a telescope. Due to this, the eighth and ninth terga get overlapped by the seventh.

The tenth tergum projects backward and is deeply notched. The tenth tergum also bears a pair of small, many jointed anal cerci.

The anal cerci are sensory. Being many jointed and freely projecting at the rear, they pick up faint air currents from behind the animal — which is exactly the direction from which it cannot see.

This rear-facing air-current sense is why a cockroach so often escapes just before a foot or a rolled newspaper lands on it. The moving object pushes a small gust of air ahead of itself; the anal cerci detect that gust and trigger a running escape response before the blow arrives.

Telling Male from Female

In the male, the abdomen is narrow and tapering compared with that of the female. In the male, the ninth sternum also bears a pair of short, unjointed anal style.

Male vs Female cockroach — external features | Feature | Male | Female | |—|—|—| | Shape of abdomen | Narrow and tapering | Comparatively broad | | Anal style on ninth sternum | Present — a pair of short, unjointed anal style | Absent | | Anal cerci | Present | Present |

Anal cerci vs Anal style Anal cerci are a pair of small, many jointed structures borne on the tenth tergum, and are present in both sexes. The anal style is a pair of short, unjointed structures borne on the ninth sternum, and is present only in the male. “Many jointed and on the tergum” versus “unjointed and on the sternum” is the distinction to remember.

Q5. If you were handed two cockroaches, how could you tell the male from the female without dissecting either of them?

A. Look at the hind end of the abdomen. The male has a narrow, tapering abdomen and carries a pair of short, unjointed anal style on the ninth sternum. The female has a comparatively broader abdomen and no anal style. Both sexes carry anal cerci, so the cerci are of no use in telling them apart.

11.4 Body Cavity

A body cavity, or true coelom, is present around the viscera — that is, around the internal organs such as the gut and the reproductive organs. Having a true coelom is what makes the cockroach eucoelomate, as you saw when studying its general body plan.

Why It Is Called a Haemocoel

In most animals, blood is confined to vessels and the body cavity holds only a watery fluid. In the cockroach the circulation is of the open type, so blood leaves the vessel and washes freely over the organs. Because of this, the body cavity is filled up with blood. Hence, it is called the haemocoel.

NoteDefinition

The haemocoel is the body cavity (true coelom) of the cockroach, which — because circulation is of the open type — is filled with blood instead of coelomic fluid, so that the blood bathes the viscera directly.

Coelom vs Haemocoel A coelom is any true body cavity lined by mesodermal tissue, and it is normally filled with coelomic fluid. A haemocoel is that same cavity when it has become filled with blood because circulation is open. So every haemocoel is a coelom, but not every coelom is a haemocoel.

Fat Bodies

In the haemocoel, fat bodies are seen. A fat body is in the form of a loose, whitish mass of tissue lying freely in the cavity, in contact with the blood on all sides.

The fat body is made up of large, polygonal cells which contain fat globules, proteins and sometimes glycogen. All three of these are food reserves, so the fat body works as the insect’s store-room — it takes up nutrients from the blood when food is plentiful and releases them back when the animal is starving, moulting or forming eggs.

fat body Loose whitish tissue lying free in the haemocoel → bathed in blood on every side → nutrients can be absorbed from and released into the blood without any duct or vessel → the insect can stock up fat, protein and glycogen and draw on them whenever food runs short.

Q. Why can a cockroach survive for weeks in a cupboard where there is nothing to eat?

A. Because its fat bodies hold reserves of fat globules, protein and glycogen. As the blood in the haemocoel washes over these cells, stored material is released into it and carried to the tissues. The insect lives on its own store until food is available again.

the haemocoel Zoom out: the haemocoel is the single large cavity that occupies the whole inside of the body, between the exoskeleton and the viscera. Zoom in: floating in it are the fat bodies, and each fat body is built of large polygonal cells packed with fat globules, proteins and sometimes glycogen.

11.5 Digestive System of Cockroach

The digestive system of the cockroach consists of the mouth parts, the alimentary canal and a pair of salivary glands. You have already studied the mouth parts, which prepare the food outside the mouth; here you will follow what happens to that food once it goes in.

The alimentary canal is a long tube, about 6-7 cm in length, of different diameters and with two openings. The two openings are the mouth at the front and the anus at the rear, so food always travels in one direction only.

The changing diameter is worth noticing. Wherever the canal widens, food is being stored or acted upon slowly; wherever it narrows, food is simply being moved along.

The alimentary canal is divisible into three regions — the Foregut (stomodaeum), the Mid-gut (mesenteron) and the Hindgut (proctodaeum). The whole system is shown in Fig. 11.6, and the path food takes through it in FC 11.4.

Diagram

Fig. 11.6 – Digestive system of cockroach, labelled: pharynx, salivary gland, salivary reservoir, oesophagus, crop, gizzard, hepatic caeca, mesenteron or midgut, Malpighian tubules, ileum, colon, rectum

Flowchart

FC 11.4 – Path of food through the alimentary canal: mouth (pre-oral cavity) → pharynx → oesophagus → crop → gizzard → [end of foregut] → stomach/ventriculus + hepatic caecae → [end of midgut] → ileum → colon → rectum → anus

The Mouth

The mouth, or pre-oral chamber, is a narrow space bounded by the mouth parts. The hypopharynx is present at the centre of the mouth, and the salivary duct opens at the base of the hypopharynx.

This arrangement means saliva is released exactly where chewing is happening, so the food is moistened at the very moment it is being crushed. The mouth then opens into the foregut.

Fore-gut (Stomodaeum)

The foregut consists of the pharynx, oesophagus, crop and gizzard. Broadly, this region receives, stores and grinds the food — no digestion of the food’s chemical content is completed here.

The pharynx is a very short, narrow but muscular tube. Being muscular, it can pull food inward. It contains taste sensillae, which are small sensory structures that test the food before it goes further, and it leads to the oesophagus.

The oesophagus is a slightly long and narrow tube. It opens into the crop and simply carries food backwards.

The crop is a large, pear-shaped, sac-like organ. It temporarily stores the food and then sends it to the gizzard. Because it can hold a large meal, the cockroach can feed quickly at night and then retire into a crevice to process the food at leisure.

Q. Why does a nocturnal insect benefit from having a large storage crop?

A. Because time spent in the open is dangerous. A crop lets the cockroach swallow a large quantity of food in a few minutes, then run back into a dark crevice. Digestion continues in safety, rather than while the animal stands exposed on a kitchen floor.

The gizzard, also called the proventriculus, is a small, spherical organ. Internally, it is provided with a circlet of six chitinous teeth and backwardly directed bristles.

The teeth are responsible for crushing the food, while the bristles help in filtering the food. Because the bristles point backwards, they let fine, well-ground particles pass on but hold back coarse ones for further grinding. A transverse section of the gizzard, showing the teeth, the circular muscles and the longitudinal grooves, is given in Fig. 11.7. The foregut ends with the gizzard.

Diagram

Fig. 11.7 – T. S. of gizzard, labelled: longitudinal groove, circular muscles, chitinous teeth arranged in a circlet

gizzard Thick circular muscles in the wall → squeeze the food chamber powerfully; six hard chitinous teeth arranged in a circlet → crush food from all sides at once; backwardly directed bristles behind the teeth → filter, letting only fine particles through → food reaches the midgut already ground and sieved, so enzymes can act on it quickly.

Crop vs Gizzard The crop is large, pear-shaped and thin-walled, and it only stores food temporarily. The gizzard is small, spherical and muscular, with chitinous teeth, and it grinds and filters food. Storage first, grinding after.

Q3. A cockroach already has hard jaws outside its mouth. Why does it then need a set of six teeth inside its food canal as well?

A. Because the mandibles outside can only cut and crush food coarsely, and swallowing happens quickly. The six chitinous teeth in the gizzard complete the job inside the body, grinding the swallowed food finely, while the backwardly directed bristles filter it. Enzymes can only act on the surface of food particles, so this second, finer grinding greatly increases the surface area available for digestion in the midgut.

Mid-gut (Mesenteron)

The midgut consists of the stomach and the hepatic caecae. This is the region where chemical digestion and absorption actually take place.

The stomach, also called the ventriculus, is straight, short and narrow. It is lined by glandular epithelium, which secretes digestive enzymes. Hence, the stomach is mainly responsible for digestion and absorption.

The hepatic caecae are thin, transparent, short, blind (closed) and hollow tubules. Blind means each tubule is closed at its free end, so it is a pocket rather than a through-passage.

The hepatic caecae secrete digestive enzymes and thus help in digestion of food. Being several in number and projecting outward from the gut, they add a large secreting surface without making the gut itself any longer.

NoteDefinition

Hepatic caecae are the thin, transparent, short, blind and hollow tubules arising at the beginning of the midgut of the cockroach, which secrete digestive enzymes and thus help in the digestion of food.

Hepatic caecae vs Malpighian tubules Both are fine tubules attached to the gut, and both hang in the haemocoel. The hepatic caecae arise at the junction of the foregut and midgut and are digestive — they pour enzymes into the gut. The Malpighian tubules arise at the junction of the midgut and hindgut and are excretory — they pour nitrogenous waste into the gut. Front end, digestion; rear end, excretion.

Hind-gut (Proctodaeum)

The hindgut consists of the ileum, colon and rectum. Nothing is digested here; this region deals with waste and, importantly, with saving water.

The ileum is the short and narrow part of the hind-gut. The Malpighian tubules open in the anterior lumen of the ileum, near the junction of the mid-gut with the hind-gut. The posterior region of the ileum contains a sphincter, a ring of muscle that controls the passage of material onward. The ileum sends nitrogenous wastes and undigested food towards the colon.

The colon is the longer and wider part of the hind-gut. It sends the waste material towards the rectum, and it reabsorbs water from the wastes as per need — that is, the amount reclaimed depends on how much water the insect can spare at the time.

The rectum is oval or spindle-shaped and is the terminal part of the hind-gut. It contains six rectal pads along its internal surface for absorption of water.

The rectum opens outside by the anus. The anus is present on the ventral side of the 10th segment. The anus is the last or posterior opening of the digestive system, and it gives out the undigested food.

rectal pads Six thickened pads along the inner surface of the rectum → they greatly increase the absorbing surface in contact with the waste → water is drawn back from the waste into the body → the faeces leave as dry pellets and very little water is lost.

This is why cockroach droppings are small, dry, dark pellets rather than moist smears. Pest-control workers look for exactly these dry pellets, together with shed exoskeletons, in cupboard corners: their presence shows an active population even when no live cockroach is seen. The dryness itself is evidence of how efficiently the colon and rectal pads reclaim water — a real advantage for an animal living in dry kitchen cupboards.

order of the regions and their parts Foregut — Pharyngeal Opening Carries Grain: Pharynx, Oesophagus, Crop, Gizzard. Midgut — Stomach with hepatic caecae. Hindgut — Ileum, Colon, Rectum (“I C Rubbish”). Always recite the three regions front to back before naming their parts.

Salivary Glands

The cockroach has a pair of salivary glands which secrete saliva. Each gland consists of two glandular lobes and one receptacle or reservoir, as shown in Fig. 11.10.

Diagram

Fig. 11.10 – Salivary glands of cockroach, labelled: glandular part, lobular salivary duct, common salivary duct, reservoir or receptacle, reservoir duct, common reservoir duct, common efferent salivary canal, hypopharynx

The glandular lobes consist of many irregular-shaped white lobules, and these lobules secrete saliva. The receptacle of each gland is a thin-walled, elongated, sac-like structure, and it stores the saliva until it is needed.

Now follow the ducts, because the arrangement is easy to lose track of. Each gland has a salivary duct, and both these ducts unite together to form a common salivary duct. Each receptacle has a duct, and these ducts unite to form a common reservoir duct.

Both common ducts — that is, the common salivary duct and the common reservoir duct — unite together to form the common efferent salivary duct. The efferent salivary duct opens at the base of the tongue, or hypopharynx. The whole branching pattern is summarised in FC 11.5.

Flowchart

FC 11.5 – Salivary duct system: (a) glandular lobules → salivary duct of each gland → common salivary duct; (b) receptacle of each gland → reservoir duct → common reservoir duct; then common salivary duct + common reservoir duct → common efferent salivary duct → opens at base of hypopharynx

Q. Why does the cockroach need a reservoir when the lobules can secrete saliva directly?

A. Because secretion is slow but feeding is sudden. The lobules keep making saliva quietly between meals and the receptacle holds it ready. When the insect starts chewing, a large amount of stored saliva can be released at once through the common efferent duct — far more than the lobules could produce on the spot.

Food and Digestion

The cockroach is omnivorous and feeds upon plant and animal material. It has chewing and biting type of mouth parts, which chew the food and push it into the alimentary canal.

As food passes through the alimentary canal, it is digested, and finally the undigested food is eliminated through the anus.

a fragment of chapati from the kitchen floor to the anus 1. The mouth parts chew the fragment in the pre-oral cavity, while saliva from the efferent salivary duct wets and softens it. 2. It is drawn through the muscular pharynx, whose taste sensillae test it, and passes down the oesophagus. 3. It is stored temporarily in the large, pear-shaped crop while the cockroach retreats to a crevice. 4. In the gizzard, six chitinous teeth crush it and backwardly directed bristles filter it, letting only fine particles pass. 5. In the stomach, enzymes from the glandular epithelium and from the hepatic caecae digest it, and the products are absorbed. 6. Undigested residue enters the ileum, where nitrogenous waste from the Malpighian tubules joins it. 7. In the colon, water is reabsorbed from the waste as needed. 8. In the rectum, the six rectal pads absorb still more water, leaving a dry pellet. 9. The pellet leaves through the anus on the ventral side of the 10th segment.

Cockroaches eat young cockroach. Such a tendency is called cannibalism.

11.6 Circulatory System or Blood Vascular System

The cockroach has an open type of circulatory system. It consists of colourless blood, called haemolymph, a dorsal blood vessel made up of the heart and the dorsal aorta, and the haemocoel.

“Open” means the blood does not stay inside vessels all the way round. It is pumped out of the single vessel, spills into the body cavity, bathes the organs directly, and then finds its way back — so the body cavity itself is part of the circulatory pathway.

NoteDefinition

An open circulatory system is one in which blood leaves the blood vessel and flows freely through the body cavity, bathing the organs directly, instead of being confined to a closed network of arteries, veins and capillaries.

Open circulation vs Closed circulation In open circulation (cockroach) blood leaves the vessel and fills the body cavity, so blood and cavity fluid are the same thing and the pressure is low. In closed circulation (earthworm, humans) blood stays inside vessels throughout, cavity fluid is separate, and the pressure is much higher.

A. Haemolymph

The haemolymph of the cockroach is without any pigment; hence it is colourless. This is a striking difference from our own blood, whose red colour comes from the respiratory pigment haemoglobin.

Because there is no respiratory pigment, the haemolymph does not carry oxygen. Oxygen supply is handled entirely by a separate set of air tubes, which you will meet in the next section.

The haemolymph consists of plasma and seven types of blood cells, or haemocytes. Plasma consists of water with some dissolved organic and inorganic solutes.

The plasma is rich in nutrients and in nitrogenous wastes like uric acid. So the fluid carries food to the tissues and carries waste away from them — transport of nutrients and wastes, rather than of gases, is its main job.

colourless haemolymph No respiratory pigment → the blood cannot carry oxygen → oxygen delivery is taken over by the tracheal system, which reaches every tissue directly → the blood is left free to specialise in carrying nutrients, wastes and blood cells at low pressure.

Q. If haemolymph carries no oxygen, why does the cockroach need a heart at all?

A. Because the blood still has to move. Nutrients absorbed from the midgut must be delivered to muscles and reproductive organs, wastes must be carried to the Malpighian tubules, and haemocytes must reach injured tissue. Without a pump, the fluid in the haemocoel would simply sit still and this exchange would stop.

Why is the body cavity of the cockroach called a haemocoel?

B. Haemocoel

The body cavity, or coelom, of the cockroach is divided into three sinuses by two diaphragms — the dorsal diaphragm and the ventral diaphragm. A sinus here simply means one of the compartments of the cavity through which blood flows.

The dorsal and ventral diaphragms are thin fibromuscular septa (singular: septum). Fibromuscular means they contain both fibres and muscle, so they are partitions that can actively change shape rather than fixed walls. Each remains attached to the terga along the lateral sides at intermittent points — that is, it is anchored at intervals rather than continuously, which is what leaves gaps for blood to pass through.

The dorsal diaphragm has 12 pairs of fan-like alary muscles — 2 thoracic pairs and 10 abdominal pairs. Alary muscles are triangular, with the pointed end attached to the terga at the lateral side and the broad end lying between the heart and the dorsal diaphragm.

Set out that way, the alary muscles form a fan on either side of the heart. When they contract, they pull the dorsal diaphragm flat; when they relax, it bulges upward. That simple change of shape is what drives blood in and out of the space around the heart.

The ventral diaphragm is flat and present just above the ventral nerve cord. Laterally, it is attached to the sterna at intermittent points.

Diagram

Fig. 11.9 – Transverse section of the cockroach’s abdomen showing the three sinuses, labelled: tergum, heart in pericardial sinus, dorsal diaphragm with alary muscles, perivisceral sinus with gut and fat bodies, ventral diaphragm, perineural sinus with ventral nerve cord, sternum

Sinuses

The coelom of the cockroach gets divided into three sinuses — the pericardial, perivisceral and perineural sinus. Their names tell you their positions: cardium is heart, viscera are the internal organs, and neural refers to the nerve cord.

The pericardial sinus is dorsal, very small, and contains the dorsal vessel.

The perivisceral sinus is the middle and the largest of the three. It contains the fat bodies and almost all the major visceral organs of the alimentary canal and the reproductive system.

The perineural sinus is ventral and small, and it contains the ventral nerve cord. It is continuous into the legs, which is how blood reaches the limbs even though no vessel runs into them.

All the three sinuses communicate with each other through pores present between two successive points of attachment of the diaphragms. This is exactly why the diaphragms are attached only at intermittent points — continuous attachment would seal the compartments off from one another and circulation would be impossible.

The three sinuses of the haemocoel | Feature | Pericardial sinus | Perivisceral sinus | Perineural sinus | |—|—|—|—| | Position | Dorsal | Middle | Ventral | | Size | Very small | Largest | Small | | Bounded by | Above the dorsal diaphragm | Between the two diaphragms | Below the ventral diaphragm | | Contains | Dorsal blood vessel | Fat bodies, major visceral organs of alimentary canal and reproductive system | Ventral nerve cord | | Special feature | Blood enters the heart from here through ostia | Blood returns here after systole | Continuous into the legs |

naming the three sinuses “Peri” means around. Pericardial — around the heart. Perivisceral — around the viscera. Perineural — around the nerve cord. If you can recall what lies in each compartment, its name follows automatically.

Dorsal Blood Vessel

The dorsal blood vessel is present in the pericardial sinus, just below the tergum. It is divisible into a posterior heart and an anterior aorta, which is also called the dorsal aorta or cephalic vessel.

The heart is about 2.5 cm long. It is a narrow, muscular tube that is open anteriorly and closed posteriorly. Because the rear end is sealed and only the front end is open, blood pushed along the tube can travel in one direction only — forwards, towards the head.

It starts from the 9th abdominal segment and extends anteriorly up to the 1st thoracic segment. It is divisible into thirteen chambers: ten chambers are in the abdominal region and three are in the thoracic region.

Each chamber has a pair of vertical slit-like incurrent apertures or openings called ostium (plural: ostia). “Incurrent” means they let blood in, not out. The ostia are present along the lateral side, in the posterior region of the first 12 chambers.

Each ostium has lip-like valves that allow flow of blood from the sinus to the heart only. These valves are what make an open system work in an orderly way: blood can be drawn in from the pericardial sinus, but it cannot leak back out when the chamber squeezes.

ostia with lip-like valves Slit-like openings in the wall of each heart chamber → blood in the pericardial sinus can enter the heart along its whole length; lip-like valves that open inwards only → blood cannot escape back into the sinus during contraction → every squeeze of the heart drives blood forward towards the head instead of sideways.

The heart is continued by a short, thin-walled vessel called the dorsal aorta. It lies in the head region and opens into the haemocoel — there is no vessel beyond this point, which is precisely what makes the system open. The whole arrangement is shown in Fig. 11.11.

Diagram

Fig. 11.11 – Circulatory system of cockroach in dorsal view, labelled: anterior aorta, chambers of heart, ostia, alary muscles

Q. Why does the heart have thirteen chambers and ostia all along its length, instead of one large chamber like ours?

A. Because in an open system blood collects all along the body, not at two fixed veins. A long tube with a pair of ostia in almost every chamber can draw blood in at many points at once. The wave of contraction then moves from the rear forwards, so each chamber passes its contents to the next — many small pumps in series rather than one big one.

Blood Circulation in Cockroach

Blood circulates between the sinuses and the heart due to the contraction and relaxation of the heart and the alary muscles. Note that two structures share the work: the heart drives blood forward, while the alary muscles control the space around it.

The heart alternately contracts (systole) and relaxes (diastole). After diastole, there is a third phase in the heart cycle known as diastasis, in which the heart remains in the expanded state. So the cycle here has three phases, not two.

During diastole, the alary muscles contract, making the dorsal diaphragm flat. This enlarges the pericardial sinus. As a result, blood passes from the perivisceral sinus to the pericardial sinus through the fenestrae, and finally into the heart through the ostia.

During systole, contraction starts at the posterior end and a wave of contraction passes anteriorly. Because of this, blood is pushed towards the cephalic vessel, that is, the dorsal aorta. During systole, the ostia remain closed with the help of their valves, so none of the blood escapes sideways.

As a result of systole, blood is flushed into the head region, from where it goes to the perivisceral and perineural sinuses. The blood thus returns to the body cavity, washes over the organs and the nerve cord, and becomes available to be collected again.

The alary muscles are relaxed during systole. Due to this, the dorsal diaphragm becomes convex, reducing the volume of the pericardial sinus. This makes the blood move from the pericardial sinus to the perivisceral sinus through the fenestrae. The complete cycle is summarised in FC 11.6.

Flowchart

FC 11.6 – One complete circulation cycle: diastole — alary muscles contract → dorsal diaphragm flattens → pericardial sinus enlarges → blood moves perivisceral sinus → pericardial sinus through fenestrae → enters heart through ostia → systole — contraction wave passes from posterior end forwards → ostia closed by valves → blood pushed into dorsal aorta → flushed into head region → passes into perivisceral and perineural sinuses; alary muscles relax → dorsal diaphragm becomes convex → pericardial sinus shrinks → blood moves pericardial sinus → perivisceral sinus through fenestrae → diastasis — heart remains expanded → back to diastole

two different “fenestrae” In the head, fenestrae are the small white ocellar spots at the base of each antenna. In the circulatory system, fenestrae are the pores of the diaphragm through which blood moves from one sinus to another. Same word, completely different structures — always read which region is being discussed.

a drop of haemolymph through one full cycle 1. The drop lies in the perivisceral sinus, among the gut and fat bodies. 2. The alary muscles contract, flattening the dorsal diaphragm and widening the pericardial sinus above it. 3. The drop is drawn upward through a fenestra into the pericardial sinus. 4. It enters a heart chamber through a pair of slit-like ostia, whose lip-like valves open inwards. 5. Systole begins at the rear; the wave of contraction travels forward and the valves shut the ostia. 6. The drop is pushed from chamber to chamber towards the front of the heart. 7. It leaves through the dorsal aorta and is flushed out into the head region. 8. From the head it flows back into the perivisceral and perineural sinuses, bathing the viscera, the nerve cord and the legs. 9. During diastasis the heart lies expanded and the drop waits in the sinus for the next cycle to draw it in again.

Because the organs sit directly in the flowing blood, anything that reaches the haemolymph reaches every tissue quickly, with no vessel walls or capillary barriers in the way. This is one reason insecticides that get through the cuticle or the gut act on a cockroach so rapidly — the open circulation distributes them body-wide within minutes, including to the nerve cord lying in the perineural sinus.

11.7 Respiratory System or Tracheal System

The cockroach has an internal respiratory system of air tubes called the tracheal system, by which air is brought into the body and is brought in contact with every part of the body. Instead of bringing oxygen to a blood stream, the animal simply pipes air itself to the tissues.

This system allows exchange of gases directly between the air and the tissues, without the need of blood. That is a striking difference from our own arrangement, where every molecule of oxygen must first dissolve in blood and be carried by haemoglobin before it can reach a muscle. The general plan of the system is shown in Fig. 11.12.

Diagram

Fig. 11.12 – Respiratory system of cockroach, labelled: chitin of body wall, spiracle, epithelium, chitinous lining, lumen, small tracheae, tracheoles, tracheole cell, tracheole fluid, muscle fibre

Q2. A cockroach’s blood is colourless and carries no oxygen at all — so how does oxygen still reach the muscles deep inside its body?

A. Through the tracheal system. Air enters at the spiracles and travels along a branching network of air tubes — trachea, then finer tracheae, then tracheoles — that ends blindly right inside the tissues. Oxygen therefore reaches the muscle cells as a gas, dissolving only in the film of fluid at the very tip of each tracheole. The haemolymph plays no part in transporting it.

Spiracles

Spiracles are the respiratory openings of the body. They are paired and present on the ventro-lateral side of the body, in the pleural membrane — that is, in the soft cuticle joining the tergum to the sternum, which is the only part of the body wall flexible enough to carry an opening.

Cockroaches have two pairs of thoracic spiracles and eight pairs of abdominal spiracles, making ten pairs in all — the same slit-like openings you met when studying the external morphology.

The spiracles open into a series of air sacs, from which the tubes called trachea arise. Air sacs act as reservoirs, so a fresh supply of air is held ready just inside each opening.

Trachea

The trachea form a definite pattern of branching tubes, arranged transversely as well as longitudinally. Transverse tubes carry air across the body, longitudinal tubes carry it front to back, and together they form a grid that reaches every region.

They are about 1 mm thick and have spiral or annular thickening of chitin. The inner lining of chitin prevents the trachea from collapsing.

This is important, because these are air tubes lying inside a soft, fluid-filled body cavity. Without stiffening rings they would be squashed flat every time the insect’s muscles contracted, and the air supply would be cut off. Each trachea branches into a number of smaller tubes called tracheoles.

spiral chitinous thickening of the trachea A spiral or ring-like band of chitin inside the tube wall → holds the tube permanently open like the wire in a vacuum-cleaner hose → the tube cannot be flattened by the surrounding blood or by muscle movement, and it can still bend as the body bends → an uninterrupted air path from spiracle to tissue.

Tracheoles

Tracheoles are fine intracellular tubes that penetrate deep into the tissues. Intracellular means they run right inside the cells rather than merely between them, so the delivery point is as close to the site of respiration as it can possibly be.

They are thin and are not lined with chitin. Losing the chitin lining matters: gases can now diffuse straight through the wall, which they could not do through a thick chitinous tube. Tracheoles end blindly in the cells.

Each tracheole, at its blind end, is filled with a watery fluid through which exchange of gases takes place. Oxygen from the air dissolves in this fluid and passes into the cell, while carbon dioxide passes out the same way.

The content of this fluid keeps changing. At high muscular activity, a part of the fluid is drawn into the tissues, to enable more and rapid oxygen intake. As the fluid is withdrawn, air moves further down the tracheole, so the gas comes still closer to the working cells and the diffusion distance becomes shorter.

tracheole fluid A film of watery fluid at the blind tip → gases must dissolve here before crossing into the cell; the volume of this film can be reduced during heavy activity → air advances deeper into the tissue → the distance oxygen must diffuse falls → oxygen supply rises exactly when the muscles demand it.

Q. Why does the amount of fluid in a tracheole fall when the cockroach is running hard?

A. Because the tissue becomes more concentrated as it works, and water is drawn out of the tracheole into it. This is useful rather than accidental: with less fluid in the way, air penetrates further along the tracheole and oxygen reaches the muscle faster. When the animal rests, the fluid returns.

How the Air Is Renewed

The rhythmic movements of the thoracic and abdominal muscles renew the air in the tracheal system. These pumping movements of the body squeeze and release the air sacs and tubes, driving stale air out and fresh air in through the spiracles.

The body fluid does not distribute the gases, but simply acts as a stationary medium for diffusion. In other words, the haemolymph is only the still layer that gases dissolve in and cross; the actual transport of gases through the body is done by the air tubes themselves.

Trachea vs Tracheole | Feature | Trachea | Tracheole | |—|—|—| | Origin | Arises from air sacs at the spiracles | Arises by branching of a trachea | | Diameter | About 1 mm thick | Very fine | | Chitin lining | Present, with spiral or annular thickening | Absent | | Position | Between the organs, transverse and longitudinal | Intracellular; penetrates deep into tissues | | Ending | Branches into tracheoles | Ends blindly inside the cells | | Gas exchange | Does not occur here | Occurs here, through the fluid at the blind end |

Flowchart

FC 11.7 – Path of oxygen from outside air to a muscle cell: atmospheric air → spiracle → air sac → trachea (chitin-lined, spirally thickened) → smaller tracheae → tracheole (no chitin) → tracheole fluid at blind end → cytoplasm of the tissue cell; carbon dioxide follows the same route in reverse and leaves through the spiracle

trachea of a cockroach vs trachea of a human Both are air tubes held open by stiffening rings, but they end very differently. The human trachea is a single tube that ends in the lungs, where oxygen is handed over to blood for transport. The cockroach’s trachea is one of a whole branching network that ends inside the tissues themselves, so no blood transport is involved at all.

Because air can enter only through the spiracles, anything that forms a film over the body surface can suffocate an insect. This principle is used in mosquito control, where a thin layer of larvicidal oil spread on stagnant water blocks the breathing openings of the larvae. It is the respiratory system, not any poison, that is being attacked.

Q. Why are there no insects the size of a dog?

A. Because the tracheal system depends on gases diffusing along air tubes, and diffusion becomes slow and inefficient over long distances. A very large insect could not get oxygen fast enough to the middle of its body. An animal that transports oxygen in blood, as we do, faces no such limit — which is one reason large land animals are vertebrates.

11.8 Excretory System

Malpighian tubules are the main excretory organs of the cockroach. They are attached to the alimentary canal between the midgut and the hindgut, and you can see them in that position in Fig. 11.6.

They are thin, yellow coloured, ectodermal, thread-like structures hanging freely in the haemocoel. “Hanging freely” is the key phrase — each tubule is bathed on all sides by the blood whose wastes it has to remove, so no separate supply of blood to the organ is needed.

They are about 150 in number. A large number of very fine tubules gives an enormous total surface for absorption while taking up hardly any space.

Structure of a Malpighian Tubule

Each Malpighian tubule is lined with a single layer of glandular epithelial cells having microvilli. A single layer keeps the barrier thin, and the microvilli — minute finger-like projections of the cell surface — multiply the area available for exchange many times over. The structure of one tubule is shown in Fig. 11.8.

Diagram

Fig. 11.8 – A single Malpighian tubule of cockroach, labelled: attachment at the junction of midgut and hindgut, proximal (absorptive) portion, distal (secretory) portion, single layer of glandular epithelial cells with microvilli, lumen; with an inset showing the tubules opening into the anterior lumen of the ileum

The two ends of the tubule do different jobs. Their distal portion is secretory in function and the proximal part is absorptive in function.

Malpighian tubule About 150 fine tubules hanging free in the haemocoel → each is surrounded by blood on all sides; a single layer of cells bearing microvilli → a thin barrier with a very large surface; secretory distal end and absorptive proximal end → waste is drawn in at the far end and useful water is reclaimed on the way back → efficient waste removal with very little loss of water.

How Excretion Takes Place

The tubules extract water and nitrogenous wastes from the haemocoel and convert them into uric acid, and then pass them into the ileum. From there the waste travels with the undigested food through the colon and rectum, where still more water is reclaimed, before leaving through the anus.

Notice how neatly this is arranged: the excretory organ empties into the gut instead of having an opening of its own, so a single exit serves both undigested food and nitrogenous waste. The complete route is summarised in FC 11.8.

Flowchart

FC 11.8 – Route of nitrogenous waste: water + nitrogenous wastes in haemocoel → distal secretory portion of Malpighian tubule → converted into uric acid → proximal absorptive portion reabsorbs useful water → anterior lumen of ileum → colon (water reabsorbed) → rectum (six rectal pads absorb water) → anus

As the cockroach excretes uric acid, it is said to be uricotelic.

NoteDefinition

An animal is said to be uricotelic when its main nitrogenous excretory product is uric acid — a compound that is almost insoluble in water and can therefore be got rid of with very little water loss.

Ammonotelic vs Ureotelic vs Uricotelic Ammonotelic animals excrete ammonia and need a great deal of water to dilute it, so they are usually aquatic. Ureotelic animals, such as mammals, excrete urea and need a moderate amount of water. Uricotelic animals, such as the cockroach, excrete uric acid and need almost none. The order ammonia → urea → uric acid runs from most toxic and most water-costly to least.

Uric acid excretion is not an insect peculiarity — birds and many reptiles are uricotelic too. In every case the advantage is the same: waste can be disposed of as a near-solid paste rather than a dilute solution, so water is conserved. For the cockroach this means it can live for long periods in a dry cupboard; for a bird it means less water weight to carry in flight.

Other Excretory Structures

In addition to the Malpighian tubules, the fat bodies, nephrocytes and uricose glands — the last of these in male cockroach only — also help in excretion.

In the cockroach, urate cells (nephrocytes) associated with the fat bodies and the cuticle are also believed to be excretory in function. The nephrocytes are cells present along with the fat bodies, or present along the heart, and they store nitrogenous wastes.

Storing waste rather than removing it at once is a genuine strategy, sometimes called storage excretion: the waste is locked away in a harmless form inside cells until it can be disposed of. The excretory products are later removed into the haemocoel.

Some nitrogenous wastes are deposited on the cuticle and eliminated during moulting. So each time the old exoskeleton is shed, a load of stored waste leaves the body with it.

Q. How can shedding the exoskeleton count as excretion?

A. Because nitrogenous waste has been deposited in the cuticle while it was being built. When that cuticle is cast off at moulting, the waste locked inside it leaves the body permanently. It is a slow route compared with the Malpighian tubules, but it costs the insect no water at all.

Excretory structures of the cockroach | Structure | Where it lies | Role in excretion | |—|—|—| | Malpighian tubules | Attached to the gut between midgut and hindgut, hanging in the haemocoel | Main excretory organs; extract water and nitrogenous wastes and convert them to uric acid, passed into the ileum | | Fat bodies | Free in the haemocoel | Help in excretion, in addition to storing food reserves | | Nephrocytes (urate cells) | Along with the fat bodies, or along the heart | Store nitrogenous wastes, later released into the haemocoel | | Uricose glands | In male cockroach only | Help in excretion | | Cuticle | Body surface | Some nitrogenous wastes are deposited in it and eliminated during moulting |

the excretory system Zoom out: excretion in the cockroach is not the work of one organ but of a whole set — tubules, fat bodies, nephrocytes, uricose glands and even the cuticle. Zoom in: the working unit is a single Malpighian tubule, and within it a single layer of epithelial cells whose microvilli do the actual extraction of waste from the blood.

11.9 Nervous System

The nervous system of the cockroach consists of the Central Nervous System (CNS), the Peripheral Nervous System (PNS) and the Autonomous Nervous System (ANS). Together these three receive information, decide what to do with it, and carry the orders out.

The nervous system of the cockroach is ventral, solid and ganglionated. Each of those three words is worth pausing on: ventral means the main nerve cord runs along the lower side of the body; solid means it is a compact cord without a central canal; and ganglionated means it carries swellings called ganglia at intervals, each ganglion being a cluster of nerve cell bodies acting as a local control centre.

nerve cord of a cockroach vs spinal cord of a vertebrate The cockroach has a ventral, solid, double, ganglionated nerve cord. A vertebrate such as a human has a dorsal, hollow, single spinal cord without segmental ganglia along its length. Position, structure and organisation all differ — this contrast is a favourite one-line question.

Flowchart

FC 11.9 – Organisation of the nervous system: Nervous system → (a) Central Nervous System → nerve ring (supra-oesophageal ganglia + circum-oesophageal connectives + sub-oesophageal ganglion) + ventral nerve cord (3 pairs thoracic ganglia + 6 pairs abdominal ganglia); (b) Peripheral Nervous System → nerves arising from the ganglia of the CNS; (c) Autonomous Nervous System → frontal, hypocerebral, ingluvial and ventricular ganglia + retrocerebral complex

A. Central Nervous System (CNS)

The CNS consists of the nerve ring and the ventral nerve cord.

The nerve ring is made up of the supra-oesophageal ganglia, the circum-oesophageal connectives and the sub-oesophageal ganglion. It is called a ring because these parts encircle the oesophagus — the food tube passes right through the middle of the animal’s main nerve centre.

The Brain

A pair of supra-oesophageal or cerebral ganglia is collectively known as the brain. The brain is present in the head, above the oesophagus and between the antennal bases. Its position between the antennal bases makes sense, since the antennae are the insect’s chief sense organs and their nerves have only a short distance to travel.

Each cerebral ganglion is formed by the fusion of three small ganglia — the protocerebrum, the deutocerebrum and the tritocerebrum. Fusion of separate segmental ganglia into one mass is what allows a segmented animal to have a single co-ordinating centre.

the three parts of a cerebral ganglion Proto (first) → Deuto (second) → Trito (third). The Greek number words themselves give the order, front to back.

The Sub-oesophageal Ganglion

The sub-oesophageal ganglion is bilobed and is present below the oesophagus in the head. It is also formed by the fusion of 3 pairs of ganglia.

The cerebral ganglia are connected to the sub-oesophageal ganglion by a pair of lateral nerves called the circum-oesophageal connectives, and these connectives arise from the cerebral ganglia. The whole arrangement is shown in Fig. 11.13.

Diagram

Fig. 11.13 – Central nervous system of cockroach, labelled: brain or supra-oesophageal ganglion, optic nerve, antennary nerve, labrofrontal nerve, circum-oesophageal connective, sub-oesophageal ganglion, mandibular nerve, maxillary nerve, labial nerve, prothoracic ganglion and nerves, mesothoracic ganglion and nerves, metathoracic ganglion and nerves, ventral nerve cord, 1st abdominal ganglion, abdominal nerves, 6th abdominal ganglion

Supra-oesophageal vs Sub-oesophageal ganglion The supra-oesophageal ganglia lie above the oesophagus and together form the brain; they mainly serve the eyes, antennae and labrum. The sub-oesophageal ganglion lies below the oesophagus, is bilobed, and mainly serves the mandibles, maxillae and labium. “Supra” is above and in front of the food tube, “sub” is below it.

Ventral Nerve Cord

The ventral nerve cord (VNC) arises from the sub-oesophageal ganglion. It is present along the mid-ventral position, lying in the perineural sinus — the ventral compartment of the haemocoel you studied earlier, so the cord is bathed in blood along its whole length.

It is a double nerve cord and consists of nine segmental, paired ganglia. Being double means two parallel cords run side by side, joined at each ganglion.

The first three pairs of segmental ganglia are large and are known as the thoracic ganglia. They are large because they control the legs and wings, and locomotion demands a great deal of nervous control.

Six pairs of segmental ganglia are in the abdomen. The sixth abdominal ganglion is the largest, and it is present in the 7th abdominal segment. There is no ganglion in the 6th segment.

Q. Why should the sixth abdominal ganglion be the largest of all the abdominal ganglia?

A. Because it lies at the rear end of the cord and receives the sensory nerves from the anal cerci. Those cerci detect faint air currents approaching from behind, and the signal must be turned into an escape response almost instantly. A large ganglion with many nerve cells is what makes that rapid switching possible.

a puff of air behind a cockroach becomes an escape run 1. A moving object pushes a gust of air towards the rear of the insect. 2. The many-jointed anal cerci on the tenth tergum are deflected by the gust. 3. Sensory nerves carry the signal into the sixth abdominal ganglion, the largest of the abdominal ganglia, in the 7th segment. 4. The signal travels forward along the double ventral nerve cord. 5. It reaches the three large thoracic ganglia. 6. Motor nerves from these ganglia run to the muscles of the legs. 7. The legs drive the insect forward, and it is running before the object arrives.

Because so much control is handled by ganglia spread along the ventral nerve cord rather than concentrated in the head, a cockroach that has lost its head can still stand, respond to touch and move its legs for a considerable time; it eventually dies from loss of water and inability to feed, not from the immediate loss of the brain. A vertebrate, whose control is centralised in the brain, could not survive such an injury for a moment. This is a direct consequence of a ganglionated nervous system.

B. Peripheral Nervous System (PNS)

The peripheral nervous system consists of the nerves arising from the various ganglia of the CNS. These nerves are the wiring that connects the central control centres to the sense organs and muscles.

Six pairs of nerves arise from the cerebral ganglia. They go to the eyes, antennae and labrum.

Nerves arising from the sub-oesophageal ganglion go to the mandibles, maxillae and labium — that is, to the chewing mouth parts.

Nerves arising from the thoracic ganglia go to the wings, legs and internal thoracic organs.

Nerves from the abdominal ganglia go to the abdominal organs of the respective abdominal segments. Each ganglion therefore looks after its own segment, which is exactly what you would expect in a segmented animal.

C. Autonomous Nervous System (ANS)

The autonomous nervous system consists of four ganglia and a retrocerebral complex. It controls the internal organs — chiefly the gut — without conscious involvement of the brain. Notice where each ganglion sits: every one of them is stationed on the part of the gut it controls.

1. Frontal ganglion: It is present above the pharynx and in front of the brain.

2. Hypocerebral ganglion: It is present on the anterior region of the oesophagus.

3. Ingluvial ganglion: It is present on the crop. It is also called the visceral ganglion.

4. Ventricular ganglion: It is present on the gizzard.

CNS vs PNS vs ANS | Feature | CNS | PNS | ANS | |—|—|—|—| | Main parts | Nerve ring and ventral nerve cord | Nerves arising from the ganglia of the CNS | Four ganglia and a retrocerebral complex | | Position | Head and mid-ventral line of the body | Throughout the body | On the pharynx, oesophagus, crop and gizzard | | Chief role | Receives information and issues commands | Carries signals to and from sense organs and muscles | Controls the internal (visceral) organs |

Q. Why are all four autonomous ganglia placed on the gut itself?

A. Because the gut has to keep working continuously, meal after meal, without instructions from the brain. A ganglion sitting directly on the crop or the gizzard can sense what is happening there and adjust the muscular movement locally — much faster than sending every signal up to the head and waiting for a reply.

Sense Organs

Collect the information and complete the chart:

Sense Organ Location Function
1. Antennae
2. Eyes
3. Maxillary palp
4. Labial palp
5. Anal cerci

11.10 Reproduction System

The cockroach is a dioecious organism, that is, male and female individuals are separate. Because the sexes are separate, fertilization requires two individuals to come together, and you have already seen that the male and female can be told apart from the outside by the shape of the abdomen and the presence of the anal style.

NoteDefinition

A dioecious animal is one in which the male and female reproductive organs are present in two separate individuals, so that no single animal produces both sperms and eggs.

1. Male Reproductive System

The male reproductive system consists of primary and secondary reproductive organs. The primary organs are the ones that produce the gametes; the secondary organs store them, nourish them and deliver them.

The primary sex organs, or male gonads, are called testes. They are paired and are located in the 4th to 6th abdominal segments. The male reproductive organs are shown in Fig. 11.14.

Diagram

Fig. 11.14 – Male reproductive system of cockroach, labelled: testis, vas deferens, seminal vesicle, ejaculatory duct, phallic gland (mushroom gland) with small tubules and long tubules, right phallomere, ventral phallomere, left phallomere, pseudopenis, titillator, anal cercus, caudal style

The testes produce sperms, which are carried by the vasa deferentia. The vasa deferentia are a pair of thin tubular structures arising from the testes and opening into the ejaculatory duct through the seminal vesicle. They carry sperms to the ejaculatory duct.

The ejaculatory duct opens into the male gonopore, which is situated ventral to the anus. So the reproductive opening lies just below the digestive opening at the hind end of the body. The route the sperms take is set out in FC 11.10.

Flowchart

FC 11.10 – Path of sperms in the male: testes (4th–6th abdominal segments) → vas deferens → seminal vesicle (sperms stored, glued into spermatophores) → ejaculatory duct → male gonopore (ventral to the anus)

The mushroom shaped gland, also called the utricular gland, is an accessory reproductive gland. It is present in the 6th to 7th abdominal segments. Being an accessory gland, it does not make sperms; it adds secretions that help in packaging and nourishing them.

The male gonapophyses, or phallomere, are the external genitalia of the male. These are three asymmetrical chitinous structures surrounding the male gonophore. Their asymmetry is not a defect — the three unequal pieces fit against the female’s parts in one particular way, which helps ensure that mating takes place between members of the same species.

Spermatophores

The sperms produced by the testes are stored in the seminal vesicles and are glued together in the form of bundles called spermatophores. These spermatophores are deposited in the female reproductive tract during copulation.

spermatophore Thousands of sperms glued into a single packet → the whole packet can be transferred in one act of copulation → almost no sperms are lost on the way and the transfer takes very little time → the pair need stay joined only briefly, which matters for an animal that must be ready to run.

2. Female Reproductive System

The female reproductive system also consists of primary and secondary reproductive organs. The primary reproductive organs are the ovaries.

There is a pair of large ovaries, lying laterally in the 2nd to 6th abdominal segments. Each ovary is formed of a group of 8 ovarian tubules, or ovarioles, containing a chain of developing ova. Because the ova lie in a chain, each ovariole holds eggs at different stages of development, and mature eggs become available in a steady succession rather than all at once. The system is shown in Fig. 11.15.

Diagram

Fig. 11.15 – Female reproductive system of cockroach, labelled: ovary, oviduct, common oviduct or vagina, spermatheca, collaterial glands, genital chamber, gonapophyses, vestibulum

All the ovarioles of an ovary open into the lateral oviduct of the respective side. Both lateral oviducts unite to form the common oviduct, or vagina.

The common oviduct, or vagina, opens into the genital chamber (bursa copulatrix), which is the female organ of copulation. The path of the eggs is summarised in FC 11.11.

Flowchart

FC 11.11 – Path of the ova in the female: ovarioles (8 per ovary) → lateral oviduct of that side → common oviduct or vagina → genital chamber (bursa copulatrix) → fertilization by sperms from the spermatheca → ootheca formed by secretion of collaterial glands → dropped or glued to a crevice

A sperm-storing structure called the spermatheca is present in the 6th segment, and it opens into the genital chamber. Besides this, paired accessory glands — the collaterial glands — are also present, and they too open into the genital chamber.

The female gonapophyses consist of six chitinous plates surrounding the genital pore.

spermatheca A sac that stores living sperms and opens into the genital chamber → sperms remain available long after copulation is over → each new batch of eggs can be fertilized as it passes down → a single mating can serve many successive batches, so the female need not find a partner again and again.

Spermatophore vs Spermatheca A spermatophore is the bundle of sperms made in the male’s seminal vesicles and transferred during copulation. The spermatheca is the organ in the female, in the 6th segment, that stores those sperms until eggs arrive. One is a package; the other is the store-room that receives it.

Male vs Female reproductive system | Feature | Male | Female | |—|—|—| | Primary organs | Testes, in the 4th to 6th abdominal segments | Ovaries, in the 2nd to 6th abdominal segments | | Gamete-carrying duct | Vas deferens → seminal vesicle → ejaculatory duct | Lateral oviduct → common oviduct (vagina) | | Accessory gland | Mushroom shaped or utricular gland (6th to 7th segments) | Collaterial glands | | Storage structure | Seminal vesicle, storing sperms as spermatophores | Spermatheca, in the 6th segment, storing received sperms | | Opening | Male gonopore, ventral to the anus | Genital chamber (bursa copulatrix) | | External genitalia | Male gonapophyses — three asymmetrical chitinous structures | Female gonapophyses — six chitinous plates |

Fertilization and Formation of Ootheca

Male and female cockroaches come together by their posterior ends and with the help of the phallomeres. The spermatophores are transferred to the genital chamber of the female cockroach.

The sperms are released from the spermatophore and they reach the spermatheca, where they are stored.

The eggs are discharged from both the ovaries alternately into the common oviduct and pass into the genital chamber, where they are fertilized by the sperms coming from the spermatheca. Discharging from the two ovaries by turns spreads the effort evenly between them.

The process of fertilization is internal — that is, the sperm meets the egg inside the female’s body, not in the surroundings. Internal fertilization is what makes reproduction on dry land possible, since the gametes never have to survive in open air.

NoteDefinition

Internal fertilization is the fusion of the sperm and the egg inside the body of the female, so that the gametes are never exposed to the outside environment.

Ootheca

The secretion of the collaterial glands forms a capsule around the fertilized eggs, and this capsule is called the ootheca, or egg case.

The ootheca is a dark reddish to blackish brown capsule, about 8 mm long, containing 14 to 16 fertilized eggs arranged in two rows.

Oothecae are dropped, or glued, to a suitable surface such as a crack or crevice of good humidity near the food source. The choice of site is important: the developing eggs need moisture, and the newly hatched young need food within reach.

On an average, a female produces 9 to 10 oothecae in her lifetime.

ootheca A hard capsule secreted around the eggs → protects them from drying, from being crushed and from small predators; eggs packed in two neat rows → many eggs occupy a small, easily hidden case; glued in a humid crevice near food → the young hatch into shelter with a meal close by.

NoteDefinition

The ootheca is the protective capsule, or egg case, formed by the secretion of the collaterial glands around the fertilized eggs of the cockroach.

Because the ootheca is a tough, sealed capsule, ordinary sprays do not reach the eggs inside it. This is why a treated kitchen can seem free of cockroaches for a few weeks and then be reinfested — the adults died, but the oothecae glued in crevices hatched afterwards. Pest-control workers therefore search for and remove egg cases, and repeat treatment after the eggs have had time to hatch.

Development of Eggs

The development of Periplaneta americana is paurometabolous, that is, there is development through a nymphal stage.

NoteDefinition

Paurometabolous development is a type of development in which the young hatches as a nymph that resembles the adult, and reaches the adult form through a series of moults, without any pupal stage.

The embryonic period varies as per temperature and humidity. At \(24\,^{\circ}\text{C}\) the duration is about 58 days, and at \(30\,^{\circ}\text{C}\) the duration is about 32 days.

how temperature affects the embryonic period The two figures given are 58 days at \(24\,^{\circ}\text{C}\) and 32 days at \(30\,^{\circ}\text{C}\). Read them as a pair: a rise of only six degrees nearly halves the time taken. Development is driven by enzyme-controlled reactions, and these run faster at higher temperature — so the trend is exactly what you would expect. In practical terms, a warm humid kitchen produces new cockroaches in roughly half the time a cool room does, which is why infestations build up so quickly in summer.

The stages of the life cycle follow one another as shown below and in FC 11.12.

Fertilized egg \(\longrightarrow\) Nymph \(\longrightarrow\) Adult

Flowchart

FC 11.12 – Life cycle of Periplaneta americana: fertilized egg (inside ootheca) → nymph (looks like the adult, far smaller, sexually immature, bears wing pads) → moult → next instar → repeated about 13 times → adult (with wings, sexually mature) → mating → back to fertilized egg

The nymph looks like the adult but is far smaller and is sexually immature. After sufficient growth, the nymph undergoes moulting and enters into the next instar — an instar being a stage between two successive moults.

The cockroach may undergo moulting for about 13 times before reaching the adult stage. The nymphal stages have wing pads, but only adult cockroaches have wings. The stages are shown in Fig. 11.16.

Diagram

Fig. 11.16 – Development stages of cockroach compared across four species (American, Oriental, Smokey brown, German), showing adult, nymph and ootheca of each against a scale bar

NoteDefinition

An instar is the stage in an insect’s development lying between two successive moults.

Nymph vs Larva A nymph, as in the cockroach, already resembles the adult, has wing pads, lives in the same place and eats the same food, and simply grows through moults into the adult. A larva, as in a butterfly, looks nothing like the adult, often eats different food, and must pass through a pupal stage before the adult form appears. Nymph goes with paurometabolous development; larva goes with development that includes a pupa.

Q. If a nymph already has wing pads, why can it not fly?

A. Because a wing pad is only an undeveloped flap, not a working wing. The wings enlarge and become functional at the final moult, together with sexual maturity. Until then the nymph relies entirely on running — which suits it well, since it lives in the same crevices as the adult.

reproduction in the cockroach Zoom out: reproduction links one generation of cockroaches to the next, and with 9 to 10 oothecae per female and 14 to 16 eggs in each, a single pair can found a large population in a warm kitchen. Zoom in: it all begins with one ovariole in one ovary, releasing a single ovum into the oviduct to meet a sperm stored in the spermatheca.

11.11 Interactions with Mankind

Having studied how the cockroach is built and how it works, it is worth asking what it means for us. The relationship runs both ways: the cockroach damages and endangers, but it is also useful.

Harmful Effects

1. The cockroach causes damage to household materials like clothes, shoes, paper and so on. Being omnivorous, it can feed on the starch, glue and natural fibres in these articles. They also eat and destroy food stuff.

2. They contaminate food, which then gives a typical smell and becomes unpalatable. The smell comes from the insect’s own secretions, so even food that is not eaten by the cockroach may have to be thrown away once it has walked over it.

3. As they live in sewage pipes and gutter holes, they carry with them harmful pathogens causing diseases like cholera, diarrhoea, tuberculosis, typhoid, etc. The insect itself does not fall ill; it simply picks up the organisms on its body and legs in the drain and sets them down again on our plates. This route is summarised in FC 11.13.

Flowchart

FC 11.13 – How a cockroach spreads disease: sewage pipes and gutter holes → pathogens stick to legs, body surface and gut → cockroach moves at night into kitchen → walks over food, utensils and working surfaces → pathogens deposited → food eaten by humans → cholera, diarrhoea, tuberculosis, typhoid

a mechanical carrier vs a biological vector A biological vector, such as the female Anopheles mosquito for malaria, is one inside which the pathogen actually multiplies or completes a stage of its life cycle. The cockroach is only a mechanical carrier — the pathogens merely ride on its body and legs from the drain to the food, without developing inside it. The disease risk is real either way, but the biology is different.

Beneficial Aspects

4. The cockroach serves as a part of the food chain also. Many amphibians, birds, lizards and rodents prey upon them, making them a part of the food chain. Remove the cockroach and a whole set of small predators loses a reliable food supply. They are also eaten by certain groups of people in South America, China and Myanmar.

5. The cockroach is used as an experimental animal in laboratories and for biological research, as they can be obtained easily without causing damage to ecological balance. This last point matters ethically as well as practically: a species that is abundant and quick to breed can be studied in large numbers without any population being threatened.

The cockroach — harmful and useful | Aspect | Harmful side | Useful side | |—|—|—| | Food | Eats and destroys food stuff; contaminates it and makes it unpalatable | Serves as food for amphibians, birds, lizards and rodents, and for people in South America, China and Myanmar | | Household | Damages clothes, shoes, paper and similar materials | — | | Health | Carries pathogens from sewage, causing cholera, diarrhoea, tuberculosis, typhoid | Its presence warns us that a place is unhygienic | | Science | — | Easily available experimental animal for laboratory and biological research, with no damage to ecological balance |

Q. Why is the cockroach such a convenient animal for a school or college laboratory?

A. Because it is large enough to dissect, easy to obtain in numbers, cheap to maintain, and abundant everywhere — so collecting it does no harm to any wild population. On top of that, it possesses every major organ system in a clearly visible form, which is exactly why this whole chapter could be built around a single insect.

Cockroaches are considered as bio-indicators. Their presence indicates unhygienic conditions.

NoteDefinition

A bio-indicator is an organism whose presence, absence or abundance tells us something about the condition of the environment it is living in.

Control Measures

As the cockroach is an economically harmful organism, it must be controlled in an efficient way. Some of the measures are as follows.

1. Good Sanitation: Dark and humid places of the kitchen, cupboards and trolleys must be cleaned regularly. Cracks and crevices and such areas must be filled. There should not be any place in a home where accumulation of garbage may take place.

Every one of these steps attacks something the insect needs. Cleaning removes its food, filling cracks removes its shelter, and clearing damp corners removes the moisture it depends on.

Cockroaches frequently enter homes by migrating up from sewer connections if the drain trap is dry. So always keep the drain trap filled with water.

The drain trap is the U-shaped bend you can see under a sink. When water stands in that bend it forms a seal that nothing can crawl through. If a bathroom or a spare sink goes unused for weeks, the standing water evaporates, the seal is lost, and the bend becomes an open tunnel from the sewer into the house. Simply running the tap for a few seconds in every unused drain restores the seal — a control measure that costs nothing and uses no chemicals.

2. Chemical control: Organophosphates, carbamates, pyrethroids and boric acid are efficient poisons of cockroaches. Various types of their formulations are available in the market, under various brand names.

Flowchart

FC 11.14 – Sequence of control measures, cheapest and safest first: remove food (clean kitchen, store food closed, clear garbage) → remove water and damp (dry sinks and corners, keep drain traps filled) → remove shelter (fill cracks and crevices) → then, if needed, chemical control with organophosphates, carbamates, pyrethroids or boric acid

Q. Why is sanitation placed before chemical control, rather than the other way round?

A. Because poisons kill the cockroaches that are present, but they do not remove the food, moisture and crevices that attracted them. If those remain, a fresh population moves in from the drains within weeks. Sanitation removes the cause; chemicals only deal with the symptom.

Different insects feed upon different types of food materials. For example, butterflies feed upon nectar, the female mosquito and bedbugs on human blood, and the mantis on other animals.

Depending upon the nature of food and feeding habits, different insects have different types of mouthparts. Collect images of the following mouthparts and paste them in the appropriate boxes: siphoning mouth parts (butterfly), sponging mouthpart (housefly), piercing and sucking mouthpart (female mosquito), piercing and sucking (bed bug), chewing and biting (praying mantis), chewing and lapping (honey bee). For each one, write a line on how the mouthpart suits that insect’s food.

Collect information about the techniques and objectives of rearing cockroaches in countries like China, and make a PowerPoint presentation including video clips.

Visit the nearest sericulture farm and study the life cycle of the silk worm. Compare its development with the paurometabolous development of the cockroach.

11.12 Summary

  1. The cockroach is omnipresent, preferring damp, moist places and crevices. It is omnivorous, nocturnal and cursorial. Periplaneta americana, Blatta orientalis and Blatta germanica are the three common species found in India.

  2. Its systematic position is Kingdom Animalia (cell wall absent, heterotrophic nutrition), Phylum Arthropoda (jointed appendages, segmented body, chitinous exoskeleton), Class Insecta (two pairs of wings, three pairs of walking legs), Genus Periplaneta (nocturnal, straight wings), Species americana (origin is in the Continent of America).

  3. The body is elongated, bilaterally symmetrical and dorso-ventrally flattened. The animal is triploblastic, eucoelomate and truly segmented, and its body cavity is a haemocoel filled with haemolymph. Its colour is glistening brown or red brown.

  4. The body is covered by a hard, waxy, tough, non-living exoskeleton of the nitrogenous polysaccharide chitin, which gives strength, elasticity and surface for muscle attachment. Each segment bears four sclerites: a dorsal tergum, a ventral sternum and two lateral pleurons.

  5. The body is divided into head, thorax and abdomen, the head being joined to the thorax by a movable neck or cervix.

  6. The head is formed by the fusion of six segments and bears a pair of antennae (tactile and olfactory, lodged in antennal sockets), fenestrae or ocellar spots at the base of each antenna, a pair of compound eyes made of ommatidia that give a mosaic image, and chewing and biting mouth parts.

  7. The mouth parts are the labrum (upper lip), mandibles (true jaws, moved by adductor and abductor muscles), maxillae (accessory jaws, with cardo, stipes, galea, lacinia and maxillary palps), labium (lower lip or second maxilla, with three-jointed labial palps) and hypopharynx or lingua, at whose base the salivary duct opens.

  8. The thorax has three segments — prothorax, mesothorax and metathorax — bearing three pairs of walking legs ventrally and two pairs of wings dorsally. Each leg has five podomeres: coxa, trochanter, femur, tibia and tarsus, the tarsus having five tarsomeres and the last one bearing claws and an arolium.

  9. The forewings (tegmina) are dark, opaque, thick and leathery and are protective; the hindwings are thin, membranous and transparent, attached to the tergum of the metathorax, and are the true wings used in flight.

  10. Ten pairs of slit-like spiracles — two thoracic and eight abdominal — open on the sides of the body.

  11. The abdomen has ten segments. Terga and sterna are joined laterally by soft pleura; the posterior segments are telescoped, the seventh overlapping the eighth and ninth. The tenth tergum bears a pair of many-jointed anal cerci. The male has a narrow, tapering abdomen and a pair of short, unjointed anal style on the ninth sternum.

  12. The body cavity is a true coelom filled with blood, hence called the haemocoel. It contains fat bodies — loose, whitish masses of large polygonal cells holding fat globules, proteins and sometimes glycogen.

  13. The digestive system consists of the mouth parts, the alimentary canal (6-7 cm long, with two openings) and a pair of salivary glands. The canal has three regions: foregut, midgut and hindgut.

  14. The foregut (stomodaeum) comprises the pharynx (with taste sensillae), oesophagus, crop (temporary storage) and gizzard or proventriculus (six chitinous teeth that crush and bristles that filter).

  15. The midgut (mesenteron) comprises the stomach or ventriculus, lined by glandular epithelium secreting digestive enzymes and responsible for digestion and absorption, and the hepatic caecae, blind tubules that also secrete digestive enzymes.

  16. The hindgut (proctodaeum) comprises the ileum (receiving the Malpighian tubules, with a sphincter at its posterior end), the colon (reabsorbs water) and the rectum (six rectal pads absorb water), opening by the anus on the ventral side of the 10th segment.

  17. Each salivary gland has two glandular lobes and a receptacle. Salivary ducts unite into a common salivary duct, reservoir ducts into a common reservoir duct, and both unite into the common efferent salivary duct, which opens at the base of the hypopharynx.

  18. Circulation is of the open type, with colourless haemolymph (plasma and seven types of haemocytes, rich in nutrients and uric acid), a dorsal blood vessel and the haemocoel.

  19. Two fibromuscular diaphragms divide the coelom into three sinuses: the small dorsal pericardial sinus (containing the dorsal vessel), the large middle perivisceral sinus (fat bodies and most viscera) and the small ventral perineural sinus (ventral nerve cord, continuous into the legs). The dorsal diaphragm bears 12 pairs of fan-like alary muscles.

  20. The dorsal blood vessel consists of the heart and the anterior or dorsal aorta. The heart is about 2.5 cm long, open in front and closed behind, running from the 9th abdominal to the 1st thoracic segment, with thirteen chambers — ten abdominal and three thoracic — and paired ostia with lip-like valves in the first 12 chambers, allowing blood to enter only from the sinus.

  21. In the heart cycle, diastole (alary muscles contract, blood enters the heart through the ostia) is followed by systole (a contraction wave from behind forwards drives blood into the dorsal aorta and thence to the head, perivisceral and perineural sinuses) and then by diastasis, in which the heart stays expanded.

  22. Respiration takes place through a tracheal system of air tubes, allowing gas exchange directly between air and tissues without blood. Air enters at the spiracles, passes into air sacs, then into trachea (about 1 mm thick, with spiral or annular chitin thickening that prevents collapse), and finally into tracheoles.

  23. Tracheoles are fine intracellular tubes without chitin, ending blindly in the cells; gas exchange occurs through the watery fluid at their blind ends, part of which is withdrawn during high muscular activity to speed up oxygen intake. Rhythmic movements of the thoracic and abdominal muscles renew the air, and the body fluid acts only as a stationary medium for diffusion.

  24. Excretion is carried out mainly by about 150 thin, yellow, ectodermal Malpighian tubules attached between the midgut and hindgut and hanging free in the haemocoel. Each has a single layer of glandular epithelial cells with microvilli, a secretory distal part and an absorptive proximal part. They convert water and nitrogenous wastes into uric acid and pass it into the ileum, so the cockroach is uricotelic.

  25. Fat bodies, nephrocytes (urate cells) and uricose glands (in the male only) also help in excretion, and some nitrogenous waste deposited on the cuticle leaves the body during moulting.

  26. The nervous system is ventral, solid and ganglionated, and consists of the CNS, PNS and ANS. The CNS has a nerve ring — supra-oesophageal (cerebral) ganglia forming the brain, circum-oesophageal connectives, and the bilobed sub-oesophageal ganglion — and a double ventral nerve cord lying in the perineural sinus with nine paired segmental ganglia: three thoracic and six abdominal. Each cerebral ganglion is formed of protocerebrum, deutocerebrum and tritocerebrum. The sixth abdominal ganglion is the largest and lies in the 7th segment; there is no ganglion in the 6th segment.

  27. The PNS is formed of nerves from the CNS ganglia: six pairs from the cerebral ganglia to the eyes, antennae and labrum; nerves from the sub-oesophageal ganglion to the mandibles, maxillae and labium; nerves from the thoracic ganglia to the wings, legs and thoracic organs; and nerves from the abdominal ganglia to the organs of their own segments.

  28. The ANS has four ganglia — frontal (above the pharynx, in front of the brain), hypocerebral (anterior oesophagus), ingluvial or visceral (on the crop) and ventricular (on the gizzard) — together with a retrocerebral complex.

  29. The cockroach is dioecious. In the male, paired testes in the 4th to 6th abdominal segments pass sperms through the vasa deferentia and seminal vesicles to the ejaculatory duct and the gonopore, which lies ventral to the anus. The mushroom or utricular gland (6th to 7th segments) is the accessory gland, and three asymmetrical chitinous phallomeres form the external genitalia. Sperms are transferred as bundles called spermatophores.

  30. In the female, paired ovaries in the 2nd to 6th abdominal segments each have 8 ovarioles. Lateral oviducts unite into the common oviduct or vagina, which opens into the genital chamber (bursa copulatrix). The spermatheca in the 6th segment stores sperms, the collaterial glands open into the genital chamber, and six chitinous plates form the female gonapophyses.

  31. Fertilization is internal. The collaterial glands secrete a capsule, the ootheca — dark reddish to blackish brown, about 8 mm long, with 14 to 16 fertilized eggs in two rows — which is dropped or glued in a humid crevice near food. A female produces 9 to 10 oothecae on average.

  32. Development of Periplaneta americana is paurometabolous, passing through a nymphal stage. The embryonic period is about 58 days at \(24\,^{\circ}\text{C}\) and about 32 days at \(30\,^{\circ}\text{C}\). The nymph resembles the adult but is smaller and sexually immature, moults about 13 times, each stage between two moults being an instar. Nymphs have wing pads; only adults have wings.

  33. Cockroaches harm us by damaging household materials, destroying and contaminating food, and carrying pathogens of cholera, diarrhoea, tuberculosis and typhoid from sewage. They are useful as part of the food chain, as food for some communities in South America, China and Myanmar, and as easily available experimental animals for research.

  34. Control is by good sanitation — regular cleaning of dark humid places, filling cracks and crevices, preventing accumulation of garbage, and keeping drain traps filled with water — and by chemical control using organophosphates, carbamates, pyrethroids and boric acid.

Flowchart

FC 11.15 – The chapter at a glance: cockroach (Periplaneta americana) → external morphology (head + thorax + abdomen, exoskeleton of chitin) → digestive system (mouth parts → foregut → midgut → hindgut → anus) → open circulatory system (haemolymph in three sinuses, heart with 13 chambers and ostia) → tracheal system (spiracles → trachea → tracheoles → tissues) → excretory system (Malpighian tubules → uric acid → ileum) → nervous system (CNS + PNS + ANS, ventral solid ganglionated) → reproductive system (dioecious → internal fertilization → ootheca) → development (fertilized egg → nymph → about 13 moults → adult) → interactions with mankind (harmful effects + useful roles + control measures)

11.13 Points to Ponder

  1. The exoskeleton protects the cockroach, yet it also forces the animal to shed its entire covering again and again. Is such a covering an advantage or a burden? What must an insect risk during the hours after a moult, when the new cuticle is still soft?

  2. Oxygen reaches the cockroach’s tissues through air tubes, while nutrients reach them through blood. What does it mean for an animal to keep these two transport jobs completely separate, and what limits does the air-tube method place on how large an insect can become?

  3. Blood in the cockroach flows at low pressure and bathes the organs directly. What kinds of activity would such a system support well, and where would it fall short compared with a closed circulation?

  4. The cockroach converts its nitrogenous waste into uric acid and loses almost no water in getting rid of it. What does this tell you about the kind of environment in which such a strategy would be favoured? Which other animals face the same problem, and how do they solve it?

  5. Much of the cockroach’s nervous control lies in ganglia spread along a ventral nerve cord rather than in the head. What are the advantages of spreading control in this way, and what abilities might an animal give up by not centralising it?

  6. The compound eye gives a mosaic image that is poor in detail but extremely quick to register movement. For an animal that lives in the dark and must escape suddenly, is this a poorer eye or a better one? What does this suggest about judging any sense organ as “good” or “bad” on its own?

  7. The cockroach begins as an egg, hatches as a nymph and grows into an adult without any pupal stage, while a butterfly passes through a pupa. What might each of these two patterns of development offer the animal that follows it?

  8. A female packs 14 to 16 eggs into a single tough capsule and glues it in a humid crevice near food. Compare this with animals that lay thousands of unprotected eggs. Which strategy would you expect in which kind of environment?

  9. The embryonic period falls from about 58 days to about 32 days when the temperature rises from \(24\,^{\circ}\text{C}\) to \(30\,^{\circ}\text{C}\). What does this suggest about how climate and season shape the size of a cockroach population, and what would you predict for a heated building in winter?

  10. Cockroaches are called bio-indicators because their presence signals unhygienic conditions. Should we then think of a cockroach infestation as the problem itself, or as a symptom of something else? How does your answer change the way you would control them?

  11. The same species is a household pest, a food item for some communities, a link in food chains, and an experimental animal in laboratories. Can any organism be called “harmful” or “useful” without saying from whose point of view?

  12. Biologists chose one common insect and studied it in complete detail to understand an entire class. What are the strengths of such a type study, and where might it mislead us if we assume all insects are built like Periplaneta americana?

11.14 Check Your Concepts

  1. The exoskeleton of the cockroach is described as “non-living”. Explain how this single fact makes moulting unavoidable for a growing nymph.

  2. Name the four sclerites covering a single body segment of the cockroach and give the position of each.

  3. Arrange the parts of a cockroach’s leg in order from the body outwards: femur, coxa, tarsus, trochanter, tibia. Which of these bears the claws and arolium?

  4. Why can a cockroach run up a smooth glass surface as well as a rough wooden one? Answer with reference to the structures on the last tarsomere.

  5. Distinguish between the forewings and the hindwings of the cockroach with respect to texture, attachment and function. Why are only the hindwings called the true wings?

  6. A cockroach’s compound eye gives a mosaic image that is poor in detail. Why, then, is it so difficult to swat a cockroach? Explain in terms of the structure of the compound eye.

  7. What is the difference between a simple eye and a compound eye? Which of the two would you expect to give better resolution, and which better detection of movement?

  8. Name the pair of structures borne on the tenth tergum of the abdomen and explain how they help the cockroach even though they lie behind its eyes.

  9. Why is the body cavity of the cockroach called a haemocoel and not simply a coelom? Which feature of its circulation makes this name appropriate?

  10. Describe the fat body of the cockroach and explain how a cockroach can survive for weeks in a cupboard with no food.

  11. Arrange in correct sequence the path taken by a food particle from the mouth to the anus, naming every region it passes through.

  12. Distinguish between the crop and the gizzard with respect to shape, wall and function.

  13. What happens to the water content of the waste as it passes through the colon and the rectum? Name the structures responsible and explain why this matters to an animal living in a dry cupboard.

  14. Both the hepatic caecae and the Malpighian tubules are fine tubules attached to the gut. State two differences between them in position and in function.

  15. Trace the route of saliva from the lobules where it is made to the point where it enters the mouth, naming every duct on the way.

  16. Name the three sinuses of the haemocoel, state what each contains, and explain how blood is able to pass from one sinus to another.

  17. Describe what the alary muscles do during diastole and during systole, and state the effect of each action on the volume of the pericardial sinus.

  18. Name the third phase of the heart cycle of the cockroach and state the condition of the heart during it. How does this cycle differ from the two-phase cycle you know in humans?

  19. What would happen to a cockroach if the chitinous spiral thickening of its trachea were absent? Explain your reasoning.

  20. Arrange in sequence the structures through which a molecule of oxygen travels from the outside air to a muscle cell of the cockroach.

  21. Why is a part of the tracheole fluid withdrawn into the tissues during heavy muscular activity? How does this help the insect?

  22. “The body fluid of the cockroach does not distribute the gases.” Justify this statement with reference to the tracheal system and to the composition of haemolymph.

  23. Why is the cockroach said to be uricotelic? Compare this with an ammonotelic and a ureotelic animal in terms of the water needed for excretion.

  24. Apart from the Malpighian tubules, name three other structures that help in excretion in the cockroach, and mention which of them is found in the male only.

  25. Explain how the shedding of the cuticle at moulting can be regarded as an excretory process.

  26. The nervous system of the cockroach is described as ventral, solid and ganglionated. Explain what each of these three words means, and contrast the arrangement with the spinal cord of a human being.

  27. In which abdominal segment does the sixth abdominal ganglion lie, and which segment has no ganglion at all? Suggest why this particular ganglion is the largest of the abdominal ganglia.

  28. A cockroach is touched gently on the anal cerci and immediately runs forward. Trace the nervous pathway of this response from the cerci to the leg muscles.

  29. Name the three ganglia whose fusion forms each cerebral ganglion, and state where in the head the brain lies.

  30. Draw a neat labelled diagram of the head of a cockroach and label the ocellar spot, compound eye, labrum, mandible, maxilla and labium.

  31. Distinguish between a spermatophore and a spermatheca, mentioning which sex each belongs to.

  32. Trace the path of a sperm from the testis of the male to the point where it fertilizes an egg inside the female, naming every structure it passes through.

  33. Describe the ootheca of the cockroach — its colour, size, contents and where it is placed — and explain how each of these features protects the developing eggs.

  34. The embryonic period of Periplaneta americana* is about 58 days at \(24\,^{\circ}\text{C}\) and about 32 days at \(30\,^{\circ}\text{C}\). What does this tell you about the effect of temperature on development, and what would you predict about cockroach populations in summer as compared with winter?*

  35. What is an instar? Arrange the following in the correct order and state approximately how many moults occur: adult, fertilized egg, nymph.

  36. Nymphal stages of the cockroach have wing pads but cannot fly. Explain, and state how a nymph differs from the larva of an insect such as a butterfly.

  37. Name two diseases whose pathogens may be carried by cockroaches, and explain how a cockroach living in a gutter comes to contaminate food in a kitchen.

  38. Why is keeping the drain trap filled with water an effective control measure? What would you expect to happen in a bathroom that is left unused for several weeks?

  39. A house is sprayed with an efficient insecticide and all visible cockroaches die, yet the infestation returns a few weeks later. Give a biological explanation based on what you have learnt about reproduction in the cockroach.

  40. Give any two reasons why the cockroach is considered a suitable animal for laboratory study, and state one way in which it is useful in nature.

  41. Give an account on tracheal system of cockroach.

  42. Describe nervous system of cockroach.

  43. With the help of a neat labelled diagram, describe the female reproductive system of cockroach.

  44. With the help of a neat labelled diagram, describe the digestive system of cockroach.

  45. A student observed that cockroaches are killed for dissection by simply putting them in soap water. He inquired whether soap is so poisonous. The teacher said it is due to their peculiar respiratory system. How?

  46. Describe the circulatory system of cockroach.

  47. How will you identify a male or a female cockroach?

  48. Write a note on: Gizzard of cockroach.

  49. Give the systematic position of cockroach.

  50. What would have happened if the cockroach did not have a gizzard?

  51. What is the functional difference between the eyes of a cockroach and a human being?

  52. What is the functional difference between the respiratory systems of a cockroach and a human being?

  53. What are anal cerci?

  54. What is a ganglion?

  55. What is the role of the hypopharynx?

  56. What is mesenteron?

  57. Location of tergum.

  58. What is ootheca?

  59. How many chambers are present in the heart of cockroach?

11.15 Objective Questions

  1. Chemical nature of chitin is ………….
    1. protein
    2. carbohydrate
    3. lipid
    4. glycoprotein
  2. Cockroach has ……………. type of mouthparts.
    1. sponging
    2. chewing and biting
    3. piercing and sucking
    4. lapping
  3. Spiracle is a part of ……………….. system of cockroach.
    1. circulatory
    2. respiration
    3. reproductive
    4. nervous
  4. ………………. is a part of digestive system.
    1. Trachea
    2. Hypopharynx
    3. Haemocyte
    4. Seminal vesicle
  5. ………………… is also called as brain of cockroach.
    1. Supra-oesophageal ganglion
    2. Sub-oesophageal ganglion
    3. Hypo-cerebral ganglion
    4. Thoracic ganglion
  6. Assertion (A): The body of the cockroach is dorso-ventrally flattened. Reason (R): The cockroach prefers to live in crevices. Choose the correct option:
    1. both A and R are true and R is the correct explanation of A
    2. both A and R are true but R is not the correct explanation of A
    3. A is true, R is false
    4. A is false, R is true.
  7. Assertion (A): The ostia of the heart of the cockroach bear lip-like valves. Reason (R): Blood must be prevented from flowing back into the pericardial sinus during systole. Choose the correct option:
    1. both A and R are true and R is the correct explanation of A
    2. both A and R are true but R is not the correct explanation of A
    3. A is true, R is false
    4. A is false, R is true.
  8. Assertion (A): Cockroaches are treated as bio-indicators. Reason (R): Their presence indicates unhygienic conditions. Choose the correct option:
    1. both A and R are true and R is the correct explanation of A
    2. both A and R are true but R is not the correct explanation of A
    3. A is true, R is false
    4. A is false, R is true.
  9. Match the following:
Column A Column B
a. Labrum i. Bears comb-like super-lingua and receives the salivary duct
b. Mandibles ii. Second maxilla, prevents loss of food while chewing
c. Maxillae iii. Upper lip, holds food during feeding
d. Labium iv. Cut and crush food by side-wise movement
e. Hypopharynx v. Bear cardo, stipes, galea, lacinia and tactile palps
  1. Match the following:
Column A Column B
a. Frontal ganglion i. Present on the gizzard
b. Hypocerebral ganglion ii. Present on the crop; also called visceral ganglion
c. Ingluvial ganglion iii. Present above the pharynx, in front of the brain
d. Ventricular ganglion iv. Present on the anterior region of the oesophagus