Wednesday, July 29, 2020

Structural Organisation In Animals - Notes | Class 11 | Part 5: Cockroach - Anatomy

7. STRUCTURAL ORGANISATION IN ANIMALS


ANATOMY OF COCKROACH

Digestive system

Alimentary canal has 3 parts: foregut, mid gut & hindgut.

·    Foregut: It is lined by cuticle. It includes

Mouth → pharynx → oesophagus → crop (to store food) gizzard (proventriculus).

Gizzard helps in grinding the food. It has an outer layer of thick circular muscles and thick inner cuticle forming 6 chitinous plates (teeth).

·    Mid gut (Mesenteron): It is not lined by cuticle. 6-8 tubules (hepatic or gastric caecae) are seen at the junction of foregut & mid gut. They secrete digestive juice.

At the junction of mid gut & hindgut, there are 100-150 yellow coloured thin filamentous Malpighian tubules.

·  Hindgut: It is broader than mid gut and lined internally by cuticle. Hindgut includes ileum, colon & rectum.  Rectum opens out through anus.

Circulatory system


-    Blood vascular system: open type.

-    Blood vessels are poorly developed and open into space (haemocoel).

-    Visceral organs located in the haemocoel are bathed in blood (haemolymph).

-    Haemolymph= colourless plasma + haemocytes.

-    Heart consists of elongated muscular tube lying along mid dorsal line of thorax and abdomen.

-    It has funnel-shaped chambers with ostia on either side.

-    Blood from sinuses enter heart through ostia and is pumped anteriorly to sinuses again.

Respiratory system


-    It consists of a network of trachea that open through 10 pairs of small holes called spiracles present on the lateral side of the body.

-    The thin branches of tracheal tubes are called tracheoles. They carry oxygen from the air to all parts.

-    The opening of the spiracles is regulated by sphincters.

-    Gas exchange takes place at the tracheoles by diffusion.

Excretory system


-    Uricotelic. Excretory organ is Malpighian tubules.

-    Each tubule is lined by glandular and ciliated cells. They absorb nitrogenous wastes and convert them into uric acid which is excreted out through the hindgut.

-    Fat body, nephrocytes & urecose glands also help in excretion.

Nervous system


-    It consists of segmentally arranged ganglia joined by paired longitudinal connectives on the ventral side.

-    3 ganglia lie in the thorax and 6 in the abdomen.

-    The head holds only a bit of nervous system. Remaining part is situated along the ventral part of the body. So, if the head of cockroach is cut off, it will still live for one week.

-    The supra-oesophageal ganglion (brain) supplies nerves to antennae and compound eyes.

-    Sense organs: Antennae, eyes, maxillary palps, labial palps, anal cerci etc.

-    Sensory receptors of antennae monitor the environment.

-    Each compound eye consists of about 2000 hexagonal ommatidia. Using these, a cockroach can receive several images of an object. This is called mosaic vision. It has more sensitivity but less resolution, being common during night (hence called nocturnal vision).

Reproductive system

Cockroaches are dioecious.


Male reproductive system:



It consists of a pair of testes, seminal vesicles, accessory glands & external genitalia.

§ Testes: Lie laterally in the 4th -6th abdominal segments.

Each testis → a thin vas deferensseminal vesicle ejaculatory ductmale gonopore.

§ Seminal vesicles: To store sperms. Sperms are glued together to form bundles called spermatophores. They are discharged during copulation.

§ Accessory glands: Include a mushroom gland (in 6th-7th abdominal segments) and phallic gland. Their secretions nourish the sperms.

§ External genitalia (male gonapophysis or phallomeres): Chitinous asymmetrical structures, surrounding the male gonopore.


Female reproductive system:



§ It consists of 2 large ovaries, oviducts, spermatheca, genital chamber, Colleterial glands etc.

§ Ovaries lie laterally in the 2nd – 6th abdominal segments. Each ovary is formed of 8 ovarian tubules (ovarioles), containing a chain of developing ova.

§ Oviducts of each ovary unite into a single median oviduct (vagina) which opens into the genital chamber.

§ A pair of spermatheca is present in the 6th segment which opens into the genital chamber.

§ Sperms are transferred through spermatophores. Their fertilised eggs are encased in oothecae.

§ Ootheca is dark reddish to blackish brown capsule, 8 mm long. Females lay 9-10 oothecae, each contain 14-16 eggs.

-   Development of P. americana is paurometabolous, (development through nymphal stage).

-   Nymphs look like adults. They moult 13 times to reach the

adult form. The next to last nymphal stage has wing pads. Only adult cockroaches have wings.


ECONOMIC IMPORTANCE OF COCKROACH

They are pests because they destroy food and contaminate it with their smelly excreta. They also transmit bacterial diseases like cholera, typhoid, tuberculosis etc.

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