In this article we will discuss about:- 1. Habitat of Cockroach 2. External Morphology of Cockroach 3. Body Cavity 4. Alimentary System 5. Vascular System 6. Respiratory System 7. Excretory System 8. Nervous System 9. Receptor Organs 10. Reproductive System.
Contents:
- Habitat of Cockroach
- External Morphology of Cockroach
- Body Cavity of Cockroach
- Alimentary System of Cockroach
- Vascular System of Cockroach
- Respiratory System of Cockroach
- Excretory System of Cockroach
- Nervous System of Cockroach
- Receptor Organs in Cockroach
- Reproductive System in Cockroach
1. Habitat of Cockroach:
The cockroach is a common household pest found in warm places such as godowns, kitchens and storerooms which offer protection as well as food. It hides in dark corners of the cellar during the daytime and comes out at night. There are several species of domestic cockroaches of which Periplaneta americana is the commonest and the largest.
In this species, both sexes are winged and the wings are longer than the length of the body. In P. orientalis (Blatta orientalis), the female has rudimentary wings and the male has short wings not reaching up to the end of its body. The young of both species are wingless.
2. External Morphology of Cockroach:
The cockroach is a bilaterally symmetrical and metamerically segmented animal. Its body is covered by a brown chitinous cuticle which forms the rigid exoskeleton. The flat and elongated body enables the animal to creep into narrow crevices.
The body is divisible into three distinct parts: head, thorax and abdomen. The head is the shortest part of the body and is composed of six segments fused together with no trace of external segmentation.
It is connected with the thorax by a narrow neck and carries important sense organs as well as mouth parts for feeding. The thorax is composed of three segments which bear the organs for locomotion, namely, three pairs of walking legs and two pairs of wings.
The abdomen lies behind the thorax and is composed of ten segments of which the first seven are distinctly visible. It carries only one pair of modified appendages called anal cerci.
Exoskeleton:
In annelid worms the epidermis of the skin is covered by a thin lining cuticle. In insects the cuticle is greatly thickened and forms a dead protective covering on the outer side of the body. Such a structure is known as exoskeleton.
It is largely composed of two substances, chitin and cuticulin, both of which are nitrogenous compounds insoluble in water, acids and alkalies. The exoskeleton supports and protects internal organs and provides attachment to muscles.
In cockroach, the cuticle is thickened in every segment of the body, forming hard plates called sclerites which are jointed to one another. In between the sclerites, narrow strips of cuticle remain thin and flexible so that the thickened plates on either side may be bent and moved. The exoskeleton of the head is known as the head capsule.
It consists of:
(1) A pair of epicranial plates joined by a median suture and covering the dorsal and posterior parts of the head;
(2) A clypeus in front, to which is hinged;
(3) The upper lip or labrum;
(4) A gena on each side, forming the cheeks.
The exoskeleton of each segment of the thorax and the abdomen consist of two parts:
(1) A dorsal sclerite called tergum or notum, and
(2) A ventral sclerite or sternum.
The pro-notum, that is the tergum of the first thoracic segment is the largest of the lot; it is triangular in shape, with the broad base directed backwards. The thoracic sterna are smaller in comparison to the terga.
The terga and sterna of the abdomen are transversely placed arched plates; the terga project laterally beyond the sterna. The posterior margins of the sclerites of one segment slightly overlap the anterior margins of those of the next. The tergum of the tenth abdominal segment is notched posteriorly.
Head and its Appendages:
The head is (Fig. 104) triangular in shape, with the broad end turned upwards and the narrow end downwards. It is held at right angles to the thorax. On each side of the head is a large bean-shaped eye. The eye is said to be compound because it is composed of a large number of visual units called ommatidia which are marked on the surface by numerous hexagonal facets.
There is a whitish patch on each side of the head just internal to the base of the antenna. This is known as the fenestra.
The head is enclosed in the head capsule and bears four pairs of jointed appendages:
(1) Antennae,
(2) Mandibles,
(3) Maxillae, and
(4) Labium.
(1) Antennae:
These are a pair of long many-jointed threadlike feelers attached to the head just in front of the eyes. The cockroach can move its antennae in every direction and uses them for feeling the way as well as for smelling the food (Fig. 103).
(2) Mandibles:
The mandibles are strongly built toothed structures placed on either side of the mouth, immediately behind the labrum. They are moved from side to side and their opposing inner edges work against each other. The mandibles are employed for cutting and crushing food.
(3) Maxillae (First Maxillae):
The two maxillae lie behind the mandibles. Each maxilla consists of two basal segments, a proximal cardo and a distal stipes, bent at an angle to one another. A five-jointed maxillary palp arises from the outer side of the stipes and is used as a feeler.
On the inner side of the palp there is a bipartite piece composed of an outer galea and an inner lacinia. The galea is hooded and helmet-like, while the lacinia terminates in a claw and bears stout bristles. The lacinia assist the mandibles by holding morsels of food and by conveying them into the mouth.
(4) Labium (Second Maxillae):
The um-paired labium is really composed of the two second maxillae which are partially fused to form the lower lip. It consists of a basal part of two segments, called submentum and mentum. Distally, the mentum bears a four-jointed labial palp on each side.
A paraglossa and a glossa are found on the inner side of each labial palp. Internally, the labium carries a small process called hypo-pharynx or tongue which projects into the oral cavity. Mandibles, maxillae and labium together with the labium of the head capsule constitute the mouth parts of the cockroach.
Thorax and its Appendages:
The thorax is composed of three segments: prothorax, mesothorax and metathorax. The narrow neck, joining the head with the prothorax is concealed by the large pro-notum. Each segment of the thorax carries a pair of walking legs. There are thus three pair of walking leg.
A leg is composed of the following thus three pairs of walking legs, five parts:
(1) A stout and flat coxa,
(2) A small trochanter,
(3) An elongated femur,
(4) A slender tibia, and
(5) A five-jointed tarsus ending in a pair of curved claws.
The terminal segment of the tarsus bears a pad called pulvillus on its ventral surface. The prothorax has no wings. The mesothorax and the meta- thorax have each a pair of wings in the adult cockroach. The wings are expressions of the cuticle supported and strengthened by vein like nervures.
The anterior wings are oval, horny structures not useful in flight; they form a protective cover for the hind-wings when the animal is resting. The anterior wings are, therefore, known as the wing-covers or elytra. The hind-wings are delicate and membranous; they are larger than the anterior pair and are folded like fans when not in use. The young cockroach has no wings.
Abdomen and its Appendages:
The abdomen is flattened dorsoventrally and clearly indicates the segmented nature of the animal. There are ten complete segments but the posterior segments are modified and telescoped under the preceding ones.
The abdomen is broader in the female than in the male. In the female cockroach, the seventh sternum is enlarged to form a boat-shaped structure which is divided into two halves. In the male cockroach, the ninth segment carries a pair of short un-jointed styles (Fig. 103) which are absent in the female.
The tergum of the tenth segment is divided into two lobes by a notch at its posterior end. Below the tergum of the tenth segment there are two triangular processes called podical plates. A pair of jointed feeler-like structures project backward from the under surface of the tenth segment in both the sexes. These are the anal cerci (Fig. 103); they represent the only true appendages of the abdomen.
External apertures:
The following openings can be detected on the external surface of the cockroach.
(1) Mouth is located anteriorly beneath the labrum and between the mandibles; the mouth parts are adapted for biting.
(2) Anus is situated posteriorly below the tergum of the tenth abdominal segment between the two podical plates.
(3) Genital opening differs in the two sexes. In the male cockroach, it lies between the tergum of the tenth and the sternum of the ninth abdominal segment, and is surrounded by chitinous rods called gonapophyses which are concerned with copulation. In (he female cockroach, it lies on the ventral surface in the sternum of the eighth segment.
(4) Respiratory opening or stigmata are ten pairs of minute apertures leading into the respiratory tubes or trachea. Of the ten, only two pairs are thoracic and the remaining are abdominal. The stigmata are situated in the soft cuticle between the terga and sterna on both sides of the body.
The first thoracic stigmata lie laterally in the mesothorax and the second similarly in the meta- thorax. The abdominal stigmata are found in the first eight abdominal segments.
3. Body Cavity of Cockroach:
The body cavity is filled with a loose tissue called fat body. It is a restricted space occupied mainly by the digestive and the reproductive organs. Blood vessels open directly into the body cavity bathing the various organs with blood. The body cavity is therefore a hoemocoele and not a true coelom. Moreover it is not lined by a coelomic epithelium as in earthworms.
4. Alimentary System of Cockroach:
The digestive system of the cockroach includes the alimentary canal and the associated digestive glands.
The alimentary canal is longer than the body of the animal and is, therefore, coiled.
It extends from the mouth in front to the anus behind and consists of three parts:
(1) Foregut,
(2) Midgut, and
(3) Hindgut.
The foregut and the hindgut are lined internally by a thick cuticle which is derived from the ectoderm of the skin. The midgut, on the other hand, is lined by a soft glandular epithelium derived from the endodeim.
The foregut or stomodaeum consists of the mouth, buccal cavity, oesophagus, crop and proventriculus or gizzard. The mouth lies between the mandibles and the maxilla, with the labrum forming an upper Up, and the labium a lower lip.
It leads into a buccal cavity, on the floor of which is a small tongue-shaped projection called hypo-pharynx. The buccal cavity opens into a narrow oesophagus, which passes through the thorax into the abdomen, where it expands to form a long and thin-walled crop. The crop is an organ for storage of food; oil and sugar may be stored here for months before they are digested and absorbed.
The crop opens into a small thick-walled conical chamber, the proventriculus or gizzard. This is a muscular organ containing in its cavity a set of six chitinous teeth for breaking up solid particles of food; behind the teeth is a ring-like cushion carrying hairs which act as a sieve and hold back larger particles from passing further ahead. The gizzard marks the termination of the stomodaeum and leads into the midgut.
The midgut or mesenteron is a narrow tube lined by columnar epithelium. It receives at its anterior end seven to eight hollow tubular structures called hepatic caeca, which secrete digestive juice into the mesenteron. It is followed by the hindgut. At the junction of the midgut and the hindgut, there are numerous fine tubes called Malpighian tubules for excretion of waste products.
The hindgut or proctodaeum is differentiated into a short and narrow anterior part called ileum, followed by a wide and somewhat coiled colon and a short dilated rectum opening into the anus. The anus is situated posteriorly beneath the tergum of the tenth abdominal segment between the two podical plates.
The digestive glands lie in the thorax and consist of a bilobed salivary gland with a reservoir or receptacle on either side of the crop. The ducts of the receptacles join to form a common tube, which receives the common ducts from the salivary glands and filially opens into the buccal cavity on the elevated hypo-pharynx.
The secretion of the glands is known as the saliva which contains amylolytic and lipolytic enzymes for digesting starch and fat. Proteins are digested by the secretion of the hepatic caeca. Solid food is taken into the mouth, masticated and digested. The digested food is absorbed into the body, while the residue is voided as faeces through the anus.
5. Vascular System of Cockroach:
Blood-vascular system is poorly developed. The blood is a colourless fluid containing numerous amoeboid leucocytes. It does not contain any respiratory pigment. There is a tubular heart enclosed in a pericardial sinus, and lying in the mid-dorsal line immediately beneath the terga of the thorax and abdomen.
It is composed of thirteen chambers each of which communicates with the pericardial sinus by a pair of ostia. From the anterior end of the heart arises the dorsal aorta which drives the blood forwards into the perivisceral space. The body cavity is a spacious hoemocoele. In the floor of the pericardial sinus are small apertures through which perivisceral hoemocoeles communicate with the pericardium.
A white substance, called fat body, occurs in the pericardial sinus and may remain scattered throughout the hoemocoele. It is believed to play some part in the storage of surplus food, such as albumen, fat and glycogen.
6. Respiratory System of Cockroach:
The cockroach has a very peculiar and well-developed respiratory system, consisting of branching air-tubes or tracheae by which air is brought directly into relationship with the tissues. The air- tubes open into the lateral sides of the body by a series of respiratory pores called spiracles or stigmata.
There are ten pairs of spiracles—the first pair in the mesothorax, the second pair in the metathorax and the remainder in the dorsolateral corners of the first eight abdominal segments. Each spiracular opening is bounded by an annular sclerite and leads into a cavity which is connected to the main tracheal trunk.
There are two large trachea trunks, one on each side, which run lengthwise and are connected to one another by transverse branches. These main tubes divide into dorsal and ventral trunks, the branches from which anastomose freely and penetrate into all parts of the body.
The air-tubes are thickened spirally on the inner side, and thus kept open. The ultimate branches ramify as fine tracheoles with no thickening. They actually run inside the tissues and organs. Oxygen is thus conveyed to all parts directly and carbon dioxide is similarly removed. This explains the poor development of the blood vascular system, as there is very little necessity of blood for the transport of respiratory gases.
Expiration is effected by contraction of the abdominal muscles resulting in the compression of the elastic tracheal tubes. When the abdominal muscles relax, the tubes regain their normal size and air flows into them through the spiracular openings. This is inspiration. The inlet and outlet of gases through spiracles may be controlled by a peculiar method— the animal closing all its breathing pores for a considerable time.
7. Excretory System of Cockroach:
The main excretory organs of the cockroach are the Maipighian tubules which float in the hoemocoelic fluid. The number of tubules vary from sixty to seventy.
Each tubule is a hollow outgrowth from the proctodaeum and is lined by glandular epithelium which secretes nitrogenous waste products. The excretory materials are principally urates and uric acid. These pass into the proctodaeum and thence out of the body, with the faeces.
8. Nervous System of Cockroach:
The nervous system of cockroach (Fig. 107) resembles that of the prawn. There is in the head a pair of supra-oesophageal ganglia or brain which supply nerves to the eyes and the antennae.
They are joined by two circum-oesophageal connectives with a sub-oesophageal ganglion, from the posterior end of which a double ventral nerve-cord runs backward. This nerve-cord is situated, as in prawn, in the midvential line, and becomes enlarged to form a ganglion in each of the three thoracic segments and in the first six abdominal segments.
The sixth abdominal ganglion is the largest and represents several ganglia fused to form a mass. From each ganglion, nerves arise and pass out to innervate the muscles, skin and appendages of the segment in which it lies. The sub-oesophageal ganglion supplies the mouth parts.
It is to be noted that the ganglia and the nerve-cord are really double in origin. They are fused medially and therefore appear as single. There is a ganglionated sympathetic nerve connected with the circum-oesophageal connectives to supply the involuntary- muscles of the alimentary canal. It lies on the dorsal surface of the crop (Fig. 107).
9. Receptor Organs in Cockroach:
The sense organs include:
(1) A pair of compound eyes,
(2) A pair of antennae said to be olfactory, tactile and gustatory in function, and
(3) Scattered sensillae in the palps, walking legs and anal cerci.
The compound eyes are not borne on eye stalks like those of the prawn. Each consists, essentially, of a large number of ommatidia. The surface of the eye is covered over by a transparent cuticle, the cornea, and subdivided into about 20,000 hexagonal facets—each of which represents an ommatidium.
The structure of an ommatidium is similar to that already described for the prawn, excepting that the pigment sheaths are not retractile. Consequently, the cockroach utilizes only the mosaic image. Though each ommatidium may form an image of the same object, these will be translated during transmission through the optic nerves, so that only one impression is registered.
The receptor cells or sensillae are isolated or collected patches of modified epidermal cells situated in various parts of the body. There are olfactory, gustatory and tactile receptors found on the antennae, palps, walking legs and anal cerci. Each sensilla is connected to a sensory nerve. The eye may be regarded as a collection of complex sensillae specially modified for vision.
The sense of smell is well-developed in the cockroach and is located mainly in the antennae. The gustatory receptors concerned with taste are found in the maxillary and labial palps.
Tactile receptors for touch are located particularly on the antennae but are also distributed generally all over the body in a scattered state. There is no definite ear in the cockroach; but certain hairs in the anal cerci are set vibrating by sound waves. These may possibly act as very simple auditory organs.
10. Reproductive System in Cockroach:
The cockroach is dioecious, that is the sexes are separate. The male can be distinguished by its anal styles which are not present in the female.
Male reproductive organs consist of:
(1) A pair of testes,
(2) A pair of vasa deferentia,
(3) A pair of seminal vesicles forming the mushroom gland,
(4) An ejaculatory duct,
(5) A conglobate gland, and
(6) The genital pouch, containing the male gonopore.
The testes appear like two small bunches of grapes, one on each side, beneath the terga of the fifth and sixth abdominal segments. The testes are active only in the young cockroach; after producing a stock of spermatozoa they become inactive and consequently they are small in the adult. A vas deferens arises from each testis and leads into the seminal vesicle of the same side.
A number of blind tubular pockets are given out from the surface of both the vesicles, so that the whole structure appears like a mushroom and is, therefore, known as the mushroom gland.
Spermatozoa formed during the early life of the animal are stored in the pockets of the latter. The seminal vesicles open into a median muscular tube called ejaculatory duct which communicates with the genital pouch by the male gonopore.
The genital pouch is a wide space between the sternum of the ninth and the tergum of the tenth abdominal segment. Lying beneath the ejaculatory duct is the conglobate gland opening separately into the genital pouch near the male gonopore. There are a number of curved chitinous hooks within the genital pouch. These are known as the gonapophyses which assist in copulation.
Female reproductive organs consist of:
(1) A pair of ovaries,
(2) A pair of oviducts,
(3) A median vagina,
(4) A pair of spermathecae of unequal size,
(5) A pair of colleterial glands, and
(6) The genital pouch, containing the gonapophyses and the female gonopore.
Each ovary consists of eight beaded tubules, the ovarioles, which Are distended posteriorly with eggs, but tapering at their freeness. The ovarioles of each ovary join posteriorly to form an oviduct. The two oviducts unite to form a median vagina, which communicates with the genital pouch by the female gonopore (Fig. 107).
The sternum of the seventh abdominal segment is large and boat-shaped. It is divided into two lateral halves which can be opened and closed like a pair of doors. The eighth and ninth abdominal sterna are tucked into the segments previous to them.
A genital pouch is thus formed which is bounded anteriorly by the eighth sternum, dorsally by the ninth sternum and ventrally by the seventh sternum. Thus the female gonopore pierces the eighth sternum to open into the genital pouch.
A pair of spermathecae open by a median aperture into the genital pouch on the ninth sternum; of the two, only one is sac-like and the other is filamentous; they receive sperms from the male during mating. The collateral glands are branched tubes opening near the female gonopore; they secrete the material for the formation of the egg-case.
There are small chitinous rods, the gonapophyses, near the opening of the genital pouch, which serve to deposit the egg-cases.