Class 11 Biology
The blood vascular system is an open type. Blood vessels are poorly developed. They open into space (haemocoel). Visceral organs located in the haemocoel are bathed in blood (haemolymph). The haemolymph is composed of colourless plasma and haemocytes. The heart consists of elongated muscular tubes which lie along mid-dorsal line of thorax and abdomen. The heart is differentiated into funnel-shaped chambers, with ostia on either side. The blood from sinuses enters the heart through ostia and is pumped anteriorly to the sinuses again.
The respiratory system consists of a network of tracheae. The tracheae open through 10 pairs of small holes, called spiracles. The spiracles are present on the lateral side of the body. There are 2 pairs of spiracles in thorax and 8 pairs in abdomen. Tracheal tubes are subdivided into tracheoles. They carry oxygen to all the parts. The opening of the spiracles is regulated by sphincters. Exchange of gases takes place by diffusion.
Malpighian tubules are the excretory organs. Each tubule is lined by glandular and ciliated cells. They absorb nitrogenous wastes and convert them into uric acid. Uric acid is excreted out through the hindgut. Additionally, fat body, nephrocytes and urecose glands also help in excretion.
The nervous system of cockroach consists of a series of fused, segmentally arranged ganglia. The ganglia are joined by paired longitudinal connectives on the ventral side. Three ganglia lie in the thorax and six in the abdomen. The nervous system in cockroach is spread throughout the body. In the head region, the brain is represented by supra-oesophageal ganglion. It supplies nerves to antennae and compound eyes.
Sense Organs: Antennae, eyes, maxillary palps, labial palps, anal cerci, etc. are the sense organs in cockroach. The compound eyes are situated at the dorsal surface of head. Each eye consists of about 2000 hexagonal ommatidia. Presence of several ommatidia gives mosaic vision to the cockroach. This gives more sensitivity but less resolution. This type of vision is common during night.
Cockroaches are dioecious.
The male reproductive system of cockroach consists of a pair of testes. The testes lie on each lateral side in the 4th – 6th abdominal segments. A thin vas deferens arises from each testis. It opens into ejaculatory duct through seminal vesicle. The ejaculatory duct opens into male gonopore which is situated ventral to anus. A typical mushroom-shaped gland is present in the 6th-7th abdominal segments. It is an accessory reproductive gland. Male gonapophysis or phallomeres represent the external genitalia. These are made up of chitin. They are asymmetrical structures and surround the male gonopore. The sperms are stored in the seminal vesicles. The sperms are glued together in the form of bundles called spermatophores. Spermatophores are discharged during copulation.
The female reproductive system of cockroach consists of two large ovaries. The ovaries lie laterally in the 2nd – 6th abdominal segments. Each ovary is formed of a group of eight ovarian tubules or ovarioles. They contain a chain of developing ova. Oviducts from each ovary unite into a single median oviduct. This is also called vagina and it opens into the genital chamber. A pair of spermatheca is present in the 6th segment which opens into the genital chamber.
Fertilization: Sperms are transferred through spermatophores. The fertilized eggs are encased in capsules, called ootheca. An ootheca is a dark reddish to blackish brown capsule. It is about 8 mm long. The oothecae are dropped or glued to a suitable surface, usually at a place with high relative humidity or near a food source. On an average, 9 – 10 ootehcae are produced by a female. Each ootheca contains 14 – 16 eggs. Development is indirect and is paurometabolous. Development through nymph stage is called paurometabolous. The nymph resembles the adults. The nymph grows by moulting about 13 times to reach the adult form. Wing pads are seen in the penultimate stage of development but wings are present only in adults.
Significance for Human: Most of the species are wild and have no economic importance. Some species live in and around human habitat. They destroy food and contaminate food with their excreta. Many bacterial diseases can be transmitted by food contamination by cockroaches.
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