- Reproduction is the only means by which the continuity of a species is maintained.
- In animals the gametes develop in the gonads by an elaborate process called gametogenesis.
- Sperm is the male gamete. It is highly specialized morphologically as well as physiologically for active motility.
- Egg is the female gamete. It contains almost all the materials which is essential for the entire process of development.
- Fertilization is the union of sperm and egg resulting in the formation of zygote.
- Fertilization maintains the diploid number of chromosomes.
- Cleavage is the segmentation of the zygote into blastomeres.
- Gastrulationis the transformation of blastula into gastrula.