Because of their complexity and functional importance, the cytological and histological processes taking place within the seminiferous tubules of mammals have attracted the attention of numerous biologists. It is remarkable that by the last quarter of the last century histologists had already interpreted accurately in terms of a dynamic time-scaled phenomenon the static histological irnages of the seminiferous epithelium they observed with the microscope. Since the various types of evolving germ cells, ie, the spermatogonia, spermatocytes, and sperrnatids at various steps of their respective development, are not arranged at random, but form well-defined cellular associations, it became evident on careful analysis that such cell associations must succeed one another in time in any given arca of the semi= niferous tubule. Since such a sequence must repeat itself indefinitely, the notion of a “cycle of the seminiferous epithelium” emerged (9, 14, 49, 109, 110). However, during the next four or five decades this phenomenon did not continue to retain such attention; it was only in the fifties that the seminiferous epithelium became the object of a renewed curiosity and intcrcst. From the numerous reviews on mammalian spermatogenesis published during the last 12 years (1, 10, 26, 39, 60, 63, 94, 105, 116), it is evident that the seminiferous epithelium of various mammals has once more come under intensive investigation.