46 Fertilization

Gametes

In the male, the four haploid cells produced by meiosis go on to develop into spermatozoa (Fig. 3.46.1), with very little cytoplasm, a nucleus containing condensed chromatin and a motile flagellum. In females, meiosis is halted in prophase I to allow for yolk production (Fig. 3.46.2) in the primary oocyte. The secondary oocyte is arrested again at metaphase II and the second meiotic division is only completed if the egg is fertilized.