Respiratory and Excretory System of Cockroach
Anatomy of Earthworm,Cockroach & Frog of Class 11
- Blood does not take part in respiration as it does not contain any respiratory pigment, so every tissue of body is in direct communication with air for gaseous exchange.
- A complicated system of numerous, shiny, transparent and branched air tubes or tracheae are found for gaseous exchange in the haemocoel cavity. There are 6 longitudinal tracheal tubes - 2 dorsal, 2 ventral and 2 lateral which are interconnected by transverse commissures. Chitinous rings prevent collapse of trachea.
- Atmospheric air enters into and escapes out from this system through ten pairs of slit-like apertures called stigmata or spiracles located on lateral sides of the body. Two pairs of these are thoracic and eight pairs are abdominal.
Fig. The main part of Tracheal System in Cockroach
- Thoracic spiracles are somewhat larger. One pair of these in between prothorax and mesothorax and the other between mesothorax and metathorax upon respective pleurities.
- The first pair of abdominal spiracles are dorso-lateral upon tergite of first abdominal segment, but the remaining seven pairs are upon the pleurities of second to eighth segments.
- Each spiracle is surrounded by a ring-like sclerite called peritreme.
Mechanism of respiration
Several tergo-sternal muscles extend vertically between the tergites and sternites of all abdominal segments. Harmonious contractions and relaxations of these at regular intervals cause rhythmic expansion and compression of entire abdomen leading to inspiration and expiration of air.
Cockroach is uricotelic. In cockroach following structures help in excretion:
(i) Malpighian tubules : Malpighian tubules are attached at the junction of mid-gut and hind-gut. Excretory products, dissolved in haemolymph and absorbed by malpighian tubules and
discharged into hindgut.
(ii) Fat bodies: Some fat bodies are also present in haemocoel, which have mycetocytes, urate cells, oenocytes and trophocytes.
(iii) Nephrocytes : Nephrocytes present in lateral wall of heart help in excretion and store nitrogenous waste.
(iv) Uricose glands: In some species, in males uricose glands are present on periphery of mushroom glands. These glands synthesize uric acid. Malpighian tubules are analogous to
mammalian kidney. Fat bodies are analogous to vertebrate liver.