Cockroach: Habitat, Locomotion and Life History

In this article we will discuss about Cockroach:- 1. Habit and Habitat of Cockroach 2. External Features of Cockroach 3. Locomotion 4. Body Wall 5. Muscles 6. Body Cavity 7. Fat Body or Cotpora Adiposa 8. Endoskeleton 9. Digestive System 10. Blood Vascular System 11. Respiratory System 12. Excretory System 13. Endocrine System 14. Copulation 15. Ootheca Formation 16. Life History 17. Metamorphosis.

Contents:

1. Habit and Habitat of Cockroach
2. External Features of Cockroach
3. Locomotion of Cockroach
4. Body Wall of Cockroach
5. Muscles of Cockroach
6. Body Cavity of Cockroach
7. Fat Body or Cotpora Adiposa of Cockroach
8. Endoskeleton of Cockroach
9. Digestive System of Cockroach
10. Blood Vascular System of Cockroach
11. Respiratory System of Cockroach
12. Excretory System of Cockroach
13. Endocrine System of Cockroach
14. Copulation in Cockroach
15. Ootheca Formation of Cockroach
16. Life History of Cockroach
17. Metamorphosis in Cockroach

1. Habit and Habitat of Cockroach:

Cockroach prefers to live in damp but warm places and generally found in kitchens, hotels, bakeries, restaurants, warehouses, grocer’s shops, sewage, ships and public latrines, etc., where plenty of food is available. It is a nocturnal animal hiding in holes and crevices during the day and coming out at night when it tastes diverse objects like clothes, shoes, books and human food to feed upon.

Thus, it is omnivorous in diet. It is a fast runner, i.e., cursorial in habit. It can also fly but it flies very rarely. It is dioecious and oviparous and exhibits parental care.

2. External Features of Cockroach:

(a) Shape, Size and Colour of Cockroach:

Its body is narrow, elongated, compressed dorsoventrally and bilaterally symmetrical. The adult cockroach measures from 2 to 4 cm in length and about 1 cm in width. The colour is reddish-brown. There are two dark patches surrounded by a light-brown margin in the first thoracic segment.

(b) Exoskeleton:

The entire body of cockroach is covered by a hard brown-coloured exoskeleton. The exoskeleton of each segment has four separate sclerites which are joined together by delicate and elastic articular membrane.

The sclerites of the dorsal side are called tergite, of ventral side are called sternite and those of lateral sides are called pleurites. The exoskeleton, in fact, consists of a thick and strong chitinous cuticle which provides protection to the body, prevents unnecessary water loss and points for the attachment of muscles.

(c) Segmentation:

It shows clear cut segmentation in its body except the head. The thorax consists of three segments and abdomen ten segments in adults which were eleven in embryo. The head is said to be formed by the fusion of six embryonic segments. However, the total body segments in embryo remain twenty but in adults only nineteen as said above.

(d) Division of Body:

Its body is clearly divisible into three regions, i.e., head, thorax and abdomen.

Head:

It is ovate and flattened anteroposteriorly and lies at right angle to the longitudinal body axis. It is highly mobile in all directions due to a flexible neck. It is formed by the fusion of six segments. The tergites of these segments have fused to form a head capsule. The head bears a pair of compound eyes, a pair of antennae and appendages around the mouth.

The top of the head capsule is called the vertex. In young cockroach, the vertex is divided by an inverted Y-shaped epicranial suture into two epicranial plates. The epicranial suture of the head capsule splits during moulting and it disappears in the adult. Below the vertex is a frons anteriorly which has a ventral clypeus.

The sclerite of the head capsule forming vertex is called occiput and the lower part of clypeus forms the upper lip or labrum. On the sides of the head capsule is a gena below each compound eye. At the back of the head is a large triangular occipital foramen which connects the cavity of the head with that of the body.

A pair of kidney-shaped sessile compound eyes are situated at the dorsolateral sides of the head. In the angle between the eyes and antennae are two small pale coloured areas called ocellar spots or fenestrae, they are undeveloped ocelli. A pair of antennae arise from membranous sockets, one on either side below the eyes.

Each antenna has three parts, a large basal scape, followed by a smaller pedicel and a long filamentous, many-jointed flagellum. Such an antenna is called filiform antenna. The antennae possess small sensory bristles and it can be moved in all possible directions. The antenna belongs to the second segment of the head.

Mouth parts:

The appendages around the mouth constitute the mouth parts which are of chewing or mandibulate or orthopterus type. The mouth parts consist of a labrum, a pair of mandibles, a pair of maxillae, a labium and a hypo-pharynx.

1. Labrum:

It is a membranous flat lobe suspended below the clypeus. It is movable due to the muscles inserted on its base. It lies in front of the mouth as the upper lip. On its ventral surface many sensory setae are situated which are possibly gustatoreceptors. Fused to the inner surface of labrum is a thin membranous plate, called the epipharynx.

2. Mandibles:

These are suspended from the sides of the head capsule, one on either side of the mouth, and have a ball and socket attachment with the head. Each mandible is stout, heavily sclerotised having teeth-like cutting plates at its inner edge. On its upper inner edge is a softer prostheca.

The mandibles are jaws used for crushing and cutting the food. The mandibles are movable with the help of adductor and abductor sets of muscles. The contraction of adductor muscles brings the mandibles closer so that their teeth are inter-fitted and in this position the food is broken down into small fragments.

Then the abductor muscles contract and the mandibles get separated from each other. So, the cutting and chewing of food is affected by the alternate contraction and relaxation of these muscles. The mandibles belong to the fourth segment of the head.

3. Maxillae:

These are two, one on either side of the head capsule behind the mandible. These are also attached with the head capsule by muscles and each of them consists of many podomeres. Each maxilla has a basal protopodite having cardo and stipes podomeres bent at right angle to each other. The cardo joins the maxilla with the head capsule.

From the outer surface of stipes arises a five-jointed maxillary palp representing the exopodite, at the base of which is a small sclerite called the palpifer. From the inner side of the stipes arises a double outgrowth consisting of an outer hood-like galea and inner lacinia which is a flat, tapering lobe ending in two sharp claw-like projections, its inner margin bears stout bristles.

The maxillae hold food by the claws of the lacinia and bring it to the mandibles for mastication. The maxillae are also used for cleaning the antennae, palps and front legs. The maxillae belong to the fifth segment of the head.

4. Labium:

It is the lower lip lying behind the mouth and represents the second pair of maxillae which have fused together into one. It has a proximal postmentum divided into a large submentum and a small poorly sclerotised mentum.

The distal part of the labium is a paired structure resembling a pair of maxillae united at their bases, it consists of prementum below the mentum and on each side it has a 3-jointed labial palp, at the base of each palp is a small sclerite, the palpiger. Between the labial palps are four lobes, two median and smaller glossae and two outer and larger paraglossae.

The labial palps are sensory and the labium does not take active part in feeding, but the glossae and paraglossae together called the ligula prevents the loss of food particles from the mandibles. The labium belongs to the sixth segment of the head. The first and third segments of the head have no appendages.

5. Hypo pharynx:

Between the maxillae and in front of the labium is flat cylindrical structure called the hypo pharynx or lingua. The common salivary duct opens at the base of the hypo pharynx.

Neck:

The neck or cervicum is a slender soft region supported by chitinous cervical plates, two dorsal and two ventral. The neck has muscles which retract and protract the head and turn it up or down or from side to side. The cockroach can also stretch its head like other insects.

Thorax:

The thorax consists of three segments, the prothorax, mesothorax and metathorax. Each segment bears a pair of walking legs and the first pair of wings arise from the mesothorax, while the second pair from the metathorax. The prothoracic segment is the largest and due to the presence of three pairs of walking legs it is also called hexapoda.

The exoskeleton of each thoracic segment is formed by four chitinous sclerites, a dorsal tergite or tergum (the thoracic terga are also called nota in insects), laterally each side has a pleurite or pleuron and ventrally there is a sternite or sternum. Between the sclerites of each segment and between the sclerites of adjacent segments are thin, soft, flexible articular or arthrodial membranes which join the sclerites.

The prothorax has a large pronotum, its anterior margin overlaps the retracted head and the posterior margin covers the bases of the wings. The mesonotum and metanotum are smaller, they are flat and rectangular with irregular lateral margins. The thoracic pleura are divided into two parts each by a vertical groove, they are an epimeron and an episternum.

Ventrally, the thorax is largely membranous, but in each segment the sternum is in the form of two one anterior and the other posterior.

Walking legs:

All the three pairs of walking legs are similar and they help the cockroach in its cursorial (fast running) habit.

Each leg consists of five segments—a large basal coxa articulating with the thoracic segment between the pleuron and sternum, coxa is followed by a smaller trochanter which is freely movable on the coxa but is fixed to the next segment, the femur which is long and broad; this is followed by a long uniformly thick tibia which bears stout bristles, the tibial spurs; the last segment is a tarsus having five movable joints or podomeres or tarsomeres which have five bristles, and their lower sides have soft adhesive pads, the plantulae.

The last tarsomere of the tarsus is often referred to as pretarsus and it terminates in two curved claws or ungues. Between the claws is a soft hollow lobe, the arolium having small bristles. The arolium is an adhesive organ for holding on the smooth surfaces.

Wings:

The wings are two pairs, the first pair arises from mesothorax and second pair from metathorax. The wings are attached to the anterolateral margin of the notum. The first pair of wings are heavily sclerotized and are known as elytra or tegmina. These are protective and cover the hind wings in a folded state, the left tegmen partly overlaps the right.

The second pair of wings are membranous and larger, they lie folded below the tegmina when at rest.

The wings are formed as outgrowths of the integument from between the notum and pleuron. Each wing has two membranous layers with tubular and chitinous prolongations of the haemocoel between them known as veins or nervures which contain blood in the early stages. Veins are strongly chitinised and enclose a small trachea; the larger veins also contain a fine nerve fibre.

The cockroach has a poorly developed set of wing muscles yet it can fly fairly well.

In flight the wings are stretched horizontally, the anterior margins of the wings remain rigid but the rest of the wings yield to air pressure as the wings are moved up and down, so that when the wing moves downward, it is curved upwards and as the wing moves upward, it is bent downwards. Hence, by becoming deflected the wings encounter pressure from behind which propels the insect through the air.

A longitudinal dorsal muscle lying below the terga raises the terga by which the wings move down. A tergosternal muscle running from the tergum to the sternum on each side of the thorax pulls the tergum down by which the wings are raised up.

Abdomen:

Abdomen consists of ten segments. The exoskeleton of the abdomen is formed of hardened sclerites. A typical abdominal segment has a dorsal tergum, ventral sternum and between them a narrow membranous pleuron on each side. Each pleuron has three sclerites, two latero-tergites arising from the tergum, and arising from the sternum is a narrow latero-sternite.

Dorsally, the abdomen has ten terga, but the 9th tergum of the male and 8th and 9th terga of the female are largely covered by the 7th tergum.

The 10th tergum is shield-shaped with a deep cleft posteriorly. The 10th tergum bears a pair of long, tapering anal cerci which is fifteen jointed. Each cercus is traversed by a nerve and it bears a sense organ which is receptive to sound. Ventrally, there are nine sterna in the male but only seven are visible externally in female.

The 9th sternum of the male has a pair of slender anal styles which are absent in female in which the 7th sternum is produced backward into a pair of large oval apical lobes or gynovalvular plates which form a keel-like structure. This rounded keel at once distinguishes the female from the male.

The 8th and 9th sterna of the female have been invaginated inwards to form a chamber-like gynatrium whose posterior part constitutes the oothecal chamber because ootheca or cocoons are formed in it. In male a group of genital structures may slightly project from the end of the abdomen.

The genital apertures of both sexes are surrounded by sclerites called gonapophyses. In the male, the gonapophyses belong to the 9th segment and they form the external genital organs or external genitalia. In female the gonapophyses belong to the 8th and 9th segments and they form an ovipositor.

In the 10th segment just below the tergum is an anus supported by four podical plates which represent the vestiges of the 11th segment and cerci are actually the appendages of this eleventh segment. The podical plates form four lobes, one on each side of the anus are called paraprocts, above the anus is a rounded epiproct, and below the anus is a small hypoproct.

The membrane between the 5th and 6th abdominal terga forms two deep pockets in the male, each pocket has two slit-like pouches which are probably glandular and produce a secretion which excites the female for copulation in the breeding season. These are called stink glands.

Some workers suggest that the secretion of these glands possesses a characteristic odour which is probably repulsive for the enemies and helps the female in detecting the presence of its mate. The male genital aperture is situated between the 9th and 10th sterna, while the female genital aperture is situated on the 8th sternum.

Spiracles:

There are ten pairs of slit-like spiracles, two on the thorax and eight on the abdomen. The first pair of thoracic spiracles lies on the pleuron between the pro-thorax and metathorax and the second pair lies between the mesothorax and metathorax. The first pair of spiracles being larger than the other.

The abdominal spiracles are smaller than the thoracic ones, the first pair lies dorsally in the first abdominal tergum, the remaining seven pairs lie on the pleuron of segments 2nd to 8th. These are the exits of respiratory system.

3. Locomotion of Cockroach:

Cockroach is a swift runner as well as a flier. The six legs are helpful in walking or running, when the cockroach is at rest, the coxae of the legs lie back against the body and the first legs are directed forward, the hind legs are stretched out posteriorly and the middle legs take whatever position is convenient.

During locomotion the first pair of leg is directed forward, they determine the course of the insect during walking or running. In locomotion on land the six legs are used as two tripods.

The first and third legs of one side and the middle leg of the other side form a triangle on which the insect rests, while the other three legs are advanced and placed on the substratum. Then the first leg pulls and the third leg pushes, the middle leg of the opposite side acts as a pivot. The process is repeated by the other three legs and the insect moves in a zig-zag fashion.

The wings are used during flight. The fore-wings are held at right angles to the body axis and they do not beat. In fact, the beating of hind-wings with the help of flight muscles helps the cockroach in flying.

The wings beat upward and downward alternately. The wings beat obliquely and at every downward beat, the wings push the air downwards and backwards. Due to this, its body is propelled upwards and forwards. Thus, by repeating this process in quick succession, cockroach flies.

4. Integument or Body Wall of Cockroach:

The body wall of cockroach consists of three distinct layers—an outermost cuticle, a cellular epidermis or hypodermis and a delicate basement membrane.

(i) Cuticle:

The cuticle is the outermost layer of the body wall and composed of chitin which hardens to form the exoskeleton. Chemically speaking, chitin is an acetate of polysaccharide of glycosamine. It is a thick layer having an outer film-like epicuticle and an inner procuticle which forms the bulk of the cuticle. The procuticle has two sub-layers, outer pigmented exocuticle and inner endocuticle.

The epicuticle is impermeable to water and permeable to gases, but in places where it is very thin it permits absorption of some water. The epicuticle has an outer layer of wax like lipoid and an inner layer of hard protein, but it has no chitin.

The outer lipoidal layer of epicuticle constitutes a highly water-proofing mechanism which checks the evaporation of water and provides an effective protection of the soft tissues against desiccation. It also helps in absorbing some water from the humidity of the atmosphere.

The epicuticle bears movable and fixed bristles. The procuticle is a thick, laminated, flexible layer of chitin. The upper part of procuticle is a laminated zone which has pigment and is sclerotised, this is often called exocuticle and it gives both rigidity and flexibility. The endocuticle is made of protein and chitin arranged in horizontal lamellae.

(ii) Epidermis:

It is a single layer of columnar epithelial cells and secretes cuticle. Some cells of the epidermis or hypodermis are modified to give rise to the movable bristles, such cells are called trichogen cells. This layer contains some dermal glands which open at the surface of the cuticle through fine dermal ducts. There are some other cells like oenocytes in addition to the dermal glands in hypodermis.

(iii) Basement Membrane:

The basement membrane is thin and structure less membranous layer lining the inner surface of the epidermis.

Functions:

1. The body wall or integument is a protective covering for the delicate internal organs.

2. The cuticle forming the exoskeleton checks the loss of water from the body by evaporation and it also provides hard surface for the attachment of muscles.

3. Different types of outgrowths from the cuticle throughout the body act as sensory, feeding, filtering, copulatory and locomotory organs.

5. Muscles of Cockroach:

The muscles are well developed and striated which provide quick movements to the body parts. The head and legs of cockroach are well muscularised, while abdomen is not so. The muscles are arranged in bundles, unlike the annelids where they constitute uniform layers in the body wall.

However, the muscles are attached to the inner surface of the chitinous skeleton. The muscles of the legs, wings and jaws are very characteristic which provide an efficient movement mechanism to these parts.

6. Body Cavity of Cockroach:

Though cockroach is a coelomate animal but its coelom is greatly reduced in the adults. The original coelom is represented by the cavities of the reproductive organs. However, the space between the body wall and gut represents the haemocoel which is filled with blood.

The haemocoel is not true coelom and it is divided into three sinuses by two horizontal muscular diaphragms which are perforated; the pericardial, perivisceral and perineural sinuses. Actually, the haemocoel relates to the blood vascular system.

7. Fat Body or Corpora Adiposa of Cockroach:

These are white, large tissue masses lying in the perivisceral sinus around the alimentary canal and the body wall. These are derived from mesoderm. The entire fat body is enclosed in a membranous connective tissue having a large number of lobes. Each lobe consists of different types of cells, of which trophocytes, mycetocytes, oenocytes and cells with urate granules are of great significance.

The trophocytes are abundant and they store not only fats but also proteins and glycogen. Thus, this cell acts as stock of the reserve food and it releases the food into the blood whenever needed. The mycetocytes harbour symbiotic microorganisms which help in the synthesis of amino acids, vitamins and glycogen from glucose.

The oenocytes synthesise some lipoproteins to form new epicuticle after each moult. Some cells absorb nitrogenous waste substances from the blood and synthesise uric acid for storage as urate granules, hence, these cells are called urate cells. However, the fat body of cockroach is in fact analogous to the vertebrate liver.

8. Endoskeleton of Periplaneta (Cockroach):

The exoskeleton, at several places most particularly in the head and thorax, extends into the body internally to form the endoskeletal elements. Such elements are called apodemes and meant for the attachment of muscles. The apodemes of the head constitute a characteristic structure called the tentorium (Fig. 73.12).

It lies below the occipital foramen in the head capsule, it has a central space for the passage of nerves and three pairs of arms—the anterior, posterior and dorsal arms. The apodemes of the thoracic region are meant for the attachment of the muscles of the legs. The abdomen has no endoskeleton.

9. Digestive System of Cockroach:

The digestive system of cockroach consists of the alimentary canal and digestive glands.

Alimentary Canal of Cockroach:

The alimentary canal starts from mouth and it consists of the preoral cavity, pharynx, oesophagus, crop and gizzard forming the foregut or stomodaeum; the mesenteron forming the midgut and the ileum, colon and rectum constituting the hindgut or proctodaeum.

The stomodaeum and proctodaeum are ectodermal in origin and lined internally by the continuation of the exoskeletal cuticle, while the mesenteron is endodermal in origin and without cuticular lining.

Foregut:

The so-called mouth is situated at the base of the pre-oral cavity or buccal chamber, also known as cibarium. The buccal chamber is a space in front of the mouth into which the food is received. This cavity is bounded in front by the labrum, posteriorly by the labium and on each side by a mandible and a maxilla. Inside this cavity a large tongue-like hypo pharynx is present.

The mouth opens behind into a short tubular pharynx which passes vertically upwards, then it bends backward into an oesophagus. The oesophagus is a narrow tubular passage which passes through the neck and gradually expands in the thorax, finally taking the shape of sac-like structure in abdomen. This sac-like structure is called crop which is thin-walled and muscular. The crop is followed by a gizzard or pro-ventriculus.

The gizzard is a round, thick-walled bulb-like structure. Structurally, it has an outer thick layer of circular muscles and its lumen gets considerably reduced due to the in-folding of its wall. The gizzard can be divided into anterior armarium and posterior stomodaeal valve.

The cuticular lining of armarium is thickened to form six highly chitinised plates called teeth. Behind the teeth, there are thin less chitinised plates which bear cushion-like pads covered with backwardly directed bristles. The deep grooves are also provided with fine bristles.

The teeth help in grinding the food, while bristles help in straining the food to allow only well crushed food to pass on. The hind part of the gizzard projects into the midgut as a funnel, called stomodaeal valve which prevents the passage of food from midgut into the gizzard.

Midgut:

The gizzard is followed by a narrow tube of uniform diameter representing the midgut or mesenteron. Its junctional region with the gizzard, which actually surrounds the stomodaeal valve, is called cardia. From this region, arise eight finger-like tubular blind processes called hepatic caeca or enteric caeca or mesenteric caeca.

The midgut is formed of tall columnar endodermal cells which are glandular in nature. The internal lining of the midgut is thrown out into small but several folds forming villi and covered by a very thin layer of transparent peritrophic membrane.

The peritrophic membrane is secreted by the anterior end of the cardia and it is permeable for enzymes and for the end products of digestion. It also protects the wall of the midgut. The process of digestion is completed in this region of the alimentary canal and the digested food is also absorbed in it.

Hindgut:

The junction of midgut and hindgut is marked by the presence of nearly sixty to one hundred fifty long, filamentous and blind Malpighian tubules which are not related with digestion but with excretion. The hindgut is relatively broader than the midgut. It is ectodermal and lined internally with the cuticle. Its anterior region following the midgut is called ileum which is followed by a long and coiled colon.

The colon ends in a broad rectum which opens by an anus lying posteriorly below the 10th tergum. The lining of the colon is wrinkled and that of the rectum forms six thick longitudinal folds called rectal papillae. The cuticle covering the papillae is very thin but its underlying epithelium is thick, this is perhaps an adaptive device for absorbing maximum water from the passing out faeces.

Digestive Glands:

Digestive glands of cockroach generally include the salivary glands, the glandular cells of the midgut and hepatic caeca.

Salivary Glands:

A pair of salivary glands (Fig. 73.16), one on either side of the crop in the thorax, are found associated with the alimentary canal. Each gland has two glandular portions and a bag-like diverticulum or receptacle or reservoir in which saliva is stored. From the glandular portions of the two sides arise salivary ducts which unite to form a common duct. Likewise, two ducts from the reservoirs also join to form another common duct.

The two common ducts join to form an efferent salivary duct which opens in the pre-oral cavity at the base of the hypo pharynx. The ducts of glands and reservoir are peculiar in having a spirally thickened cuticular lining like trachea.

Each salivary gland is made of several secreting lobules or acini. Each acinus is formed of two types of cells—zymogenic cells, packed with secretory granules and ductule containing cells with very less secretory granules but having plenty of mitochondria, rough endoplasmic reticulum and vesicular bodies.

The glandular cells of the internal lining of the midgut and hepatic caeca also produce juice containing digestive enzymes.

Food and feeding of Cockroach:

As referred earlier, cockroach is omnivorous; it feeds on every type of animal and plant materials, though it prefers to feed on sugary and starchy substances but tastes almost everything it comes across. The presence of food is detected by the sensory receptors present on the antennae and maxillary palps.

The maxillae pick up and bring food to the mandibles for mastication. During the act of mastication the teeth of the mandibles bite and chew the food.

The labrum and labium work like lips to prevent the loss of food from the mandibles at the time of mastication. The chewed food is pushed into the pre-oral cavity by maxillae, prostheca of mandibles and labium from where it is swallowed into the mouth. The function of hypo pharynx is not certain in this connection.

Physiology of Digestion:

Since salivary glands open by their common duct in the pre-oral cavity at the base of the hypo pharynx, hence, saliva mixes with the food during mastication. The saliva contains enzymes like amylase, chitinase and cellulase which hydrolyse different carbohydrates; some of them are converted into glucose. The saliva also moistens the food for its easy transport in the alimentary canal.

However, such food is swallowed by the mouth and transported through the pharynx and oesophagus into the crop. After reaching into the crop, the digested carbohydrate in the form of glucose is absorbed and remaining food comes across the secretion of the glandular cells of the midgut.

Actually, the digestive juice secreted by the glandular cells of the midgut ascends into the crop through the gizzard. This juice contains amylolytic enzymes like invertase, maltase and lactase to complete the carbohydrate digestion; proteolytic enzymes like trypsin, proteases and peptidases to digest proteins into amino acids; lipolytic enzymes for the digestion of fats into fatty acids and glycerine.

Thus, maximum digestion occurs in crop and then the food descends down through the gizzard into the midgut. The gizzard grinds and crushes the food particles into finer ones and again it filters the food with the help of the fine bristles present at its posterior region. Thus, food coming into the midgut is very fine paste-like.

The stomodaeal valves check the backward passage of food from the midgut into the crop. The inner lining of the midgut—the peritrophic membrane is permeable to digestive enzymes and digestive nutrients, therefore, the digestive enzymes meet the food to complete the digestion which is already going on.

Absorption:

The end products of digestion, i.e., proteins as amino acids, fats as fatty acids and glycerine and carbohydrates as glucose are absorbed by the lining cells of the midgut and hepatic caecae and transported to the different parts of the body for their use. The excess food material is stored in the fat body as glycogen, fat and probably albumen.

Egestion:

The undigested food passes into the hindgut. In the rectum, maximum of water is absorbed from it, hence, the undigested residue which remains here is almost solid. This is egested out in the form of small dry pellets through the anus.

10. Blood Vascular System of Cockroach:

The blood vascular system of cockroach is poorly developed and it is of open or lacunar type because the blood vessels open not into capillaries but into spaces so that the blood comes in contact directly with tissues, hence, the rate of circulation is low. However, the blood vascular system of cockroach consists of the haemocoel, blood which is called haemolymph and heart.

Haemocoel:

In the embryonic stage of cockroach, a large perivisceral coelom is found like that of an earthworm. But as the growth proceeds, the blood vessels enlarge and swell into irregular spaces and finally they completely obliterate the perivisceral coelom and replace it by such irregular spaces called sinuses or lacunae.

The sinuses join together to form the body cavity which is filled with blood and into which all the visceral organs lie. Thus, the body cavity itself is a part of circulatory system and therefore, it is called the haemocoel (haema = blood + coel = cavity), i.e., blood filled cavity. In cockroach, the haemocoel extends from anterior end of the body to the posterior end.

The haemocoel, in fact, lacks the epithelium of a true coelom and is divided into three bigger sinuses by two horizontal septa. The septa are muscular membranous structures; one dorsal diaphragm and the other ventral diaphragm.

The sinuses are upper dorsal sinus or pericardial sinus enclosing the heart, middle perivisceral sinus lodging the various visceral organs and ventral perineural sinus or sternal sinus enclosing the ventral nerve cord. Both the diaphragms are perforated so that the three sinuses remain in communication with each other.

Attached to the dorsal diaphragm is a series of paired alary muscles, they are triangular in shape and their pointed outer ends are inserted into the terga.

Heart:

The heart is an elongated tube with muscular wall, lying mid-dorsally beneath the terga of the thorax and abdomen consisting of thirteen segmentally arranged funnel-shaped chambers. At the lateral side of each chamber is a pair of ostia, one on each side, the ostia are guarded by valves which allow blood to only enter the heart.

The heart is made of a single layer of cells having striated muscles, the cells are lined both outside and inside by a delicate membrane. The first chamber of the heart is continued anteriorly into an anterior aorta which opens into haemocoel of the head.

The alary muscles are twelve pairs whose alternate contractions and relaxations cause the dorsal diaphragm ventricular to raise and fall and so results the blood to flow from perivisceral sinus to pericardial sinus and finally into the heart as it beats.

The muscular wall of the heart contracts in a wave from behind to forward and the blood is forced into the anterior aorta from where it re-enters the haemocoel and goes slowly to the organs and appendages including wings. In cockroach there is an accessory pulsatile vesicle at the base of each antenna which also pumps blood.

Haemolymph or Blood:

The haemolymph is the circulatory media in cockroach. It has colourless plasma and many corpuscles called haemocytes. No respiratory pigment is found in it. Hence, it does not help in the transport of respiratory gases. Its sole function is to transport various nutrients from one part of the body to the other and to carry nitrogenous waste substances from the tissues to the organ of excretion.

The plasma contains about 70% water and a large number of organic molecules like free amino acids, uric acid, proteins, sugars and fats, etc. The haemocytes are of three types, i.e., pro-haemocytes, transitional haemocytes and large haemocytes.

According to some workers, only two types of haemocytes are found in P. americana, the plasmatocytes and coagulocytes or cytocytes. The plasmatocytes are polymorphic and constitute nearly 60-95% of the total haemocytes. The haemocytes are phagocytic in nature, help in coagulation and haemocoel for healing the wounds.

Course of Circulation of Blood:

Wave of contraction in the heart sets from posterior to anterior end, forces the haemolymph in the anterior aorta → haemocoel of the head → ventral and perivisceral sinuses → dorsal or pericardial sinus → heart. Complete circulation of haemolymph through the body takes nearly 30 to 60 minutes.

11. Respiratory System in Cockroach:

The respiratory system of cockroach is well developed and elaborate like those of the other terrestrial insects to compensate the absence of respiratory pigment in the blood.

It consists of a system of air tubes or tracheae through which every tissue of their body remains in direct contact with the environmental air for gaseous exchange. The environmental air enters into and escapes from the tracheae through the spiracles or stigmata.

Spiracles:

There are ten pairs of spiracles or stigmata arranged segmentally; 2 pairs in the thorax and 8 pairs in the abdomen. Each spiracle is slit-like aperture in an oval sclerotized area guarded by bristles or hairs to prevent the passage of dirt. The spiracle is bordered by an annular sclerite called peritreme.

The spiracles are opened and closed by valves regulated by sphincter or spiracular muscles. This mechanism prevents undue loss of water through the spiracles and also regulates the flow of the air through them. The aperture of each spiracle leads internally into a short chamber called atrium from which arises the main tracheal trunk.

Tracheae:

The haemocoel of terrestrial insects including cockroach contains a system of network of elastic, closed, branching and silvery white tubes called tracheae. The tracheae are formed by the in pushing of the ectoderm, hence, its wall consists of three layers taenidia or intima, basement membrane and epithelium.

The intima is the cuticular lining in the form of spiral or ring-like thickenings which prevents the tracheae from collapsing. There are three pairs of large longitudinal tracheal trunks—one dorsal, one ventral and one lateral in position. All these trunks are connected by transverse commissures, thus, they anastomose to form a network which reaches to every part of the body.

The ultimate branches of tracheae end in tracheole cells from which arise very fine tubes called tracheoles.

The tracheoles have thinned cuticle lining and they end blindly in the tissue cells. In a resting insect when respiratory activity is not high, the tracheoles are filled, not with air but with a tissue fluid of cells in which oxygen dissolves. By means of this system of tracheae the cells of the body or their fluids are in direct communication with the environmental air.

However, the thoracic spiracles lead into several tracheal trunks directly, while each abdominal spiracle leads into the lateral longitudinal trunks of their sides.

Mechanism of Respiration Cockroach :

Inspiration and expiration take place through the spiracles; expiration is an active process but inspiration is passive. In cockroach the first thoracic and first abdominal spiracles remain open all the time, but the second thoracic and last seven abdominal spiracles open during inspiration and close during expiration.

Air enters the spiracles during inspiration and comes to the tracheae, then it comes to the tracheoles which contain fluids, the O₂ gets dissolved in these fluids and reaches the tissue cells.

Opening of spiracles and subsequent diffusion of air occur due to the stimulation of spiracles by carbon dioxide. In expiration some carbon dioxide may pass out through the spiracles but the major part of it diffuses out through the cuticular covering of the body. Carbon dioxide also dissolves in the plasma and reaches the body surface which is permeable to gases and allows carbon dioxide to pass out.

When active movement takes place, as in running or flying, the metabolic rate is high and the osmotic pressure of the tissues increases, as a result of these the fluid is withdrawn from the tracheoles into the body cells.

This withdrawal makes it possible for a column of air to extend deeply into tracheoles and directly reach the cells, and O₂ is taken by the fluid of the cells. In active movement the abdominal segments expand and relax, these movements are termed respiratory movements and they cause more air to be taken in through the spiracles.

Respiratory movements are coordinated by nerves in each segment, but these nerves receive impulses from thoracic ganglia which exercise a controlling influence over all respiratory activities. The coordinating centres in thoracic ganglia are stimulated and respond lack of oxygen and also to an excess of carbon dioxide.

12. Excretory System of Cockroach:

Like other insects, Malpighian tubules are the main excretory organs of cockroach. In addition, fat body, nephrocytes, cuticle and uricose glands are also excretory in function.

Malpighian Tubules:

At the junction of midgut and hindgut a large number (usually sixty to hundred fifty) of thin, long, filamentous, thread-like yellow coloured structures are found attached, which are called Malpighian tubules. The Malpighian tubules arise in six groups and hang freely in the haemocoel without any external opening into it.

These are ectodermal in origin like the nephridia of Annelida. Each Malpighian tubule is formed of a single layer of glandular ciliated cells having a characteristic brush border formed of cilia. These tubules excrete the nitrogenous wastes from the haemolymph of the haemocoel and empty the excreted substance into the gut. These are also osmoregulatory in function.

Physiology of Excretion:

The physiology of Malpighian tubule has been widely studied in different insects and it appears that it functions essentially in the same way in all the insects.

Wigglesworth has noticed two distinct regions in each tubule; a distal blind secretory region which hangs freely in the haemocoel and a proximal absorptive region which opens into the gut. The inner cells lining the distal region have well developed brush border, while in the proximal region they are less differentiated and called honey comb border.

The insects produce nitrogenous waste in the form of soluble potassium urate which is liberated into the haemolymph. These along with water are taken up by the glandular cells lining the distal region of the Malpighian tubule. In the cells of the tubule the potassium urate reacts with water and carbon dioxide (CO₂ present in the cells as a result of respiration) to form potassium bicarbonate and uric acid.

The potassium bicarbonate is absorbed back into the haemolymph but uric acid is left out in the lumen of the tubule. As the uric acid in dissolved condition moves back into the proximal region of the Malpighian tubule, the water is reabsorbed in it and passed on into the haemolymph.

The reabsorption of water occurs to such an extent that the basal part of this region becomes filled with solid crystals of uric acid. Water is further reabsorbed in the rectum, so that the passing out urine contains very little water and the bulk of it being nitrogenous waste as uric acid.

Hence, the insects are physiologically called uricotelic animals. Thus, the Malpighian tubules are excretory as well as osmoregulatory in function because they help in conserving a sufficient amount of water which has helped the insects in leading effective life activities in terrestrial habitat.

Fat Body:

As referred earlier, the fat body completely fills the haemocoel and consists of many lobules. The lobules are formed of different types of cells, some of them are urate cells which store uric acid and urate granules. Thus, the fat body also works as excretory organ in addition to its usual function of the storage of nutrients.

Nephrocytes:

These are chains of cells found along the heart in the pericardial sinus or associated with the fat body, they also store nitrogenous wastes which may be removed later by the haemolymph.

Cuticle:

During the secretion of new cuticle, some nitrogenous wastes are deposited on it and when it sheds off during moulting, the waste substance also sheds off with the cuticle.

Uricose Glands:

These glands are found associated with the mushroom-shaped gland of the male reproductive organ as long blind tubules at its periphery. These can also store uric acid and discharge it at the time of copulation over the spermatophore. These glands are also called utriculi majores.

13. Endocrine System of Cockroach:

The endocrine system of cockroach consists of inter-cerebral gland cells, corpora allata, corpora cardiaca and prothoracic glands.

Inter-cerebral Gland Cells:

These gland cells are found situated in between the two lobes of cerebral ganglion or supraoesophageal ganglion. They secrete a neurohormone called prothoracotropic or brain hormone which stimulates the prothoracic glands to secrete their secretion.

Prothoracic Glands:

After being stimulated by the neurohormone from the intercerebral glands they secrete a hormone called ecdyson which controls moulting of the nymphs. These glands are fairly large, irregular in shape and situated in the prothoracic segment. These glands get degenerate when the metamorphosis is completed.

Corpora Allata:

These are a pair of small, rounded structures situated close behind the corpora cardiaca. These glands secrete a juvenile hormone in the nymphs which helps in retaining the nymphal characters and in the last in star stage the glands become inactive. Thus, the absence of juvenile hormone allows the appearance of adult characters.

During the adult stage, these glands again become active to secrete the gonadotropic hormone. This hormone controls the development and functions of accessory reproductive glands and regulates the production of eggs in females. In a virgin female cockroach, these glands produce some volatile secretions which attract the male cockroach and, thus, it helps in finding the mate for copulation.

Corpora Cardiac:

These are a pair of elongated structures situated on either side of oesophagus behind the brain. They secrete a hormone which increases the pulsatile rate of the heart, peristalsis of the hindgut but decreases the peristalsis of the foregut. It also regulates protein metabolism. However, hormone secreted by these glands is called growth hormone.

14. Copulation in Cockroach: 

The active breeding season of cockroach starts from March and lasts up to September. Copulation occurs at night. During copulation, the male cockroach finds a suitable mate and the two partners come together by thin posterior ends. The male opens the gynovalvular plates of the female by its titillator and inserts its phallomeres into the genital chamber of the female.

The pseudopenis of the male is then inserted into the gonopore of the female and rotated transversely to hold it in position.

The anterior gonapophyses of the ovipositor are held by the right phallomere. The ventral phallomere moves to the right, thus, opening the gonopore of the ejaculatory duct, then, the spermatophore is expelled and deposited directly on the spermathecal papilla to which it is fixed in about an hour.

The phallic gland now pours its secretion on the spermatophore to form its outermost covering which hardens in about two hours. Copulation lasts for about an hour and a quarter, after which the two cockroaches separate. The sperms pass from the spermatophore into the spermathecae slowly in the course of the next 20 hours after which the empty spermatophore is discarded.

15. Ootheca Formation of Cockroach:

The eggs come alternately from the two ovaries into the common oviduct and pass through the female gonopore into the genital chamber where they are fertilised by sperms coming from the spermathecae. The two collaterial glands pour their different secretions on the fertilised eggs, these secretions combine to form a scleroprotein which hardens to form a dark brown ootheca around the eggs.

The ootheca is shaped and moulded by the ovipositor and the walls of the oothecalchamber. The ootheca is 12 mm in length, on one side it has a straight crest with a serrated margin, it contains 16 fertilised eggs standing vertically in two rows, the position of eggs can be seen on the outer surface of ootheca.

The ootheca is completed in about a day and it protrudes from the oothecal chamber, being held in place by the 10th tergum and gynovalvular plates. The female cockroach carries the ootheca for several days and finally drops it in some dark, dry place. Every female cockroach produces nearly 15 to 40 ootheca in its life span of about one to two years.

16. Life-History of Cockroach:

The eggs of cockroach, like other insects, are called centrolecithal because the ooplasm is placed in the form of a thin film outside a central mass of yolk. The embryonic development occurs in the ootheca, which takes nearly 5 to 13 weeks.

After the embryonic development is complete, the ootheca ruptures and the young ones hatch out. The young ones of cockroach resemble their parents in every respect except that they are smaller in size and without wings. These are called nymphs which undergo metamorphosis.

17. Metamorphosis in Cockroach:

The nymph of cockroach which resembles its adult in structure and feeding habit, but it is paler in colour, smaller in size, devoid of wings and the gonads are immature. As it feeds it grows, its outer exoskeleton is cast off, and this process of shedding the exoskeleton is known as moulting or ecdysis which is controlled by the hormonal activity.

During ecdysis, the hypodermis of the integument secretes an enzyme which erodes the lower surface of the old cuticle, thus, separating the cuticle from the hypodermis. Then the hypodermis secretes a new epicuticle which is impervious to the enzyme. Finally the hypodermis secretes a new procuticle.

The epicuticle and procuticle form a new cuticle. The old cuticle is ruptured and is shed by the animal. Thus, the nymph forms a new exoskeleton by its hypodermis before the old one is cast off and growth can take place only before the new covering has hardened, because the tough exoskeleton does not allow increase in size. The cockroach nymph undergoes ten to twelve ecdyses to become an adult in about a year.

During this period the nymph grows, wings are formed from the integument and gonads become mature. The ecdysis is, thus, closely associated with the growth also.

However, summing up the whole processes it can be said that the nymph gradually develops further and further from ecdysis to ecdysis. After the last ecdysis no further increase in size, i.e., growth occurs. This gradual assumption of adult characters with hardly any change is called paurornetabolic metamorphosis.

Hormonal Control of Metamorphosis:

As referred earlier, insects have three endocrine glands, out of these only two are directly related with ecdysis and growth. However, before each moult a neurosecretory hormone from the inter-cerebral gland cells of the brain known as the brain hormone or prothoracotropic hormone stimulates the prothoracic glands to release a hormone called ecdyosone or moulting hormone into the haemolymph which induces growth and moulting.

Simultaneously this hormone also stimulates all body tissues to grow and differentiate towards adulthood. At the same time another hormone called juvenile hormone is secreted from the corpora allata which regulates the rate of early growth and differentiation of tissues to have a check on undue effect of the ecdyosone.

Therefore, it has a restraining influence and checks the formation of reproductive organs and inhibits very quick metamorphic effects in the nymph. This hormone actually functions to maintain the nymph-hood during the growth phase. However, corpora allata become inactive and juvenile hormone is not produced after the last moulting.

In all the insects the interval between two ecdyses is known as stadium and the form assumed by the young insect during a stadium is called an instar. When the young hatches from an egg, it is said to be in its first instar, at the end of stadium the first ecdysis occurs and the young insect assumes its second instar, and so on. The final instar is the adult which is called imago.