FERTILISATION

The fertilisation is of two types: (i) Internal Fertilisation -In this type of fertilisation, union of male  and female gametes occurs inside the female body. e.g., birds, reptiles, and mammals (including man). But, note that the birds and reptiles "lay eggs" or are oviparous whereas mammals "produce offsprings" and  hence are viviparous". In man, fertilisation occurs in the oviduct. (ii) External Fertilisation -In this type of fertilisation , male and female animals release their sperms and eggs in surrounding medium, where fertilisation takes place, e.g., frogs, toads, fishes, etc.

Male Reproduction System

the gametes are produced by male and female reproductive structures, known as gonads. The male gonads i human beings are a pair of testes which are located in the scrotal sacs. The testes descend in foetal life in these sacs which are located outside the main body cavity. This is a physiological adaptation to ensure survival of the sperms at relatively low temperature. Besides testes, which are the main reproductive organs, there are some accessory structures, too, like a pair of vasa deferentia, seminal vesicles, ejaculatory ducts, a prostate gland and penis, etc.

Spermatogenesis

(Sperm", "genesis" = Formation): The  process of formation of sperms from the primordial mother cells is known as spermatogenesis. It involves a sequence of events underlined below.