NEET Biology Notes Structural Organisation in Animals Cockroach
Body divided into head, throax and abdomen. In each segment, exoskeleton consist of hardened plates called sclerites, joined to each other by a thin and flexible articular membrane (arthrodial membrane).
The mouth parts consists of a labrum (upper lip), a pair of mandibles, a pair of maxillae and a labium (lower lip). Each thoracic segment bears a pair of walking legs. Forewings called tegmina are opaque dark and cover the hindwings when at rest. The hindwings are transparent, membranous and are used in flight. The abdomen in both males and females consists of 10 segments. 7th segment together with the 8th and 9th sterna forms a brood or genital pouch, whose anterior part contains female gonopore, spermathecal pores and collateral glands.
In males, genital pouch lies at the hind end of abdomen bounded dorsally by 9th and 10th terga and ventrally by the 9th sternum. Males bear a pair of short, thread-like structure called anal styles, which are absent in females. In both sexes, 10th segment bears a pair of jointed filamentous structures called anal cerci.
- Digestive System
Digestive system is divisible into foregut, midnight and hindgut.
The mouth leads to pharynx followed by oesophagus, which opens into a sac-like structure called crop that is used to store food. The crop is followed by gizzard. Gizzard helps in grinding the food particles. Hepatic or gastric caecae present at the junction of foregut and midgut, secrete digestive juice. Hindgut is broader than the midgut and divisible into ileum, colon and rectum.
- Blood Vascular System
Visceral organs located in the haemocoel are bathed in blood. Heart consists of elongated muscular tube lying along the mid dorsal line of thorax and abdomen. Blood from sinuses enter in the heart through ostia and blood is pumped anteriorly to sinuses again.
- Respiratory System
Respiratory system consists of a network of trachea that opens through 10 pairs of small holes called spiracles present on the lateral side of the body. The opening of spiracles is regulated by the sphincters.
- Excretory System
Excretory system consists of Malpighian tubules present at the junction of midgut and hindgut. Malpighian tubules are 100-150 yellow coloured thin filamentous tubules. In addition, the fat body nephrocytes and urecose glands also help in excretion.
- Nervous System
Nervous system consists of a series of fused, segmentally arranged ganglia joined by paired longitudinal connectives on the ventral side.
- Sensory Organs
The sense organs in cockroach includes 4 antennae, eyes, maxillary palps, labial palps and anal cerci, etc, The compound eyes consist of 2000 hexagonal ommatidia each. A cockroach can receive several images with the help of several ommatidia. This is called mosaic vision.
- Reproductive System
Cockroaches are dioecious animals, i.e. both the sexes have well developed reproductive organs.
- Male Reproductive System
It consists of a pair of testes one lying on each side in the 4-6th abdominal segments. The sperms are stored in the seminal vesicles and are glued together in the form of bundles called spermatophores, which are discharged during copulation.
- Female Reproductive System
It consists of two large ovaries, lying laterally in the 2-6th abdominal segments. Oviducts of each ovary unite into a single median oviduct, which opens into the genital chamber.
The fertilised eggs are encased in capsules called oothecae. Development is parametabolous, i.e. through nymphal stage. The nymph looks similar to adults except difference in size.
The nymph grows by moulting about 13 times to reach the adult form. The last nymphal stage has wing pads but only adult cockroaches have wings.