The Annual Cycle of the Male Gonads (Light Microscopic Studies)

Abstract

The confinement of reproduction to an ecologically favorable period of time leads in the swan to a marked annual cycle. Apart from the obvious phases of activity in the female, the production of male germ cells capable of fertilization is also confined only to a short duration of time within a year, usually to the months of April and May in temperate northern latitudes. The preliminaries for the attainment of this goal begin already at the end of January/beginning of February. On the other hand the involution of some seminiferous tubules begins at a time when parts of the testis are still fully active. Because of the not entirely uniform development of the organ, but also because of the extensive degradation processes inside the germinal epithelium, the regression phase stretches over a comparatively long period of time, right into autumn. It continues into the resting phase which is followed again by the beginning of a new annual cycle (Figs. 20a, b).