Phases of Ovarian Cycle

In non-mammalian vertebrates the ovarian cycle consists of the following phase;

1. Pre breeding phase
2. Breeding phase and
3. Post breeding phase.

During pre breeding phase growth and differentiation of the ovarian follicles takes place. The follicles start accumulating yolk and at the end of this phase the follicles are ready for ovulation and fertilisation. Breeding phase is the period of ovulation, mating and fertilisation. This phase is followed by the post breeding phase in which ovary contains the spent follicles, or postovulatory follicles (the follicles from which the ovum is expelled during ovulation), some follicles which failed to ovulate, and atretic follicles. Degeneration and disintegration of postovulatory and atretic follicles also take place during post breeding phase.

In some of the animals there is a resting phase in which no gametoganic activity takes place. All the germ cells are at rest for some time before entering into the follicular or the pre-breeding phase. In the male animals testicular activity is a continuous process. Spermatogenesis takes place throughout the year, but spermiation (release of sperms) parallels with the ovulatory phase of the females. The reproductive cycles are regulated by-ho-pones from the pituitary and the gonads. Apart from the endogenous mechanisms, external stimuli also effect the gonadal activity.