Wednesday, October 31, 2012

Frog: Copulation

COPULATION IN FROGS

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The entry of the sperm in the egg is the basic requirement of sexual reproduction. The eggs are enveloped by liquid viscous albumin. When this albumin comes in contact water, it swells by absorbing it (water). This Albumin becomes very thick and transparent, colorless jelly. This jelly does not permit the entry of any sperm through it. The fertilization is external and in water. So it essential that the sperm should be able to enter the egg before the jelly formation. For this purpose the sperms should remain in as close a contact with egg is possible. The copulation is essential in frogs, in order to provide the maximum possible number of eggs, an opportunity for fertilization within a very short time. The frogs reproduce in monsoon in dim light. Usually when it is raining the male frogs collect near the bank of water pool or ditch. They produce croaking sound with the help of vocal sacs. The vocal sacs act as amplifiers. The croaking is a mating call for the female frogs. The female frogs getting attracted approach the male frogs. The male frog rides over the female frog and embraces it. The male frog holds the female frog firmly by its forelimbs and nuptial pads. The couple remains in this condition for 2-3 days. The Frog takes a long time to become sexually excited, as they are cold-blooded animals and devoid of copulatory organs. The male holds the female more tightly at the state of orgasm. At this stage the female discharges a large number of eggs in water from its ovisac through the cloacal aperture. The male frog right at the same moment discharges its sperms over the eggs falling in water. The two animals separate from each other on completion of this process.

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