An Electron Microscope Study of Spermatid Differentiation in the Toad, Bufo

The differentiation of the male germ cells into spermatozoa has long been a subject of particular interest to cytologists. In the period from 1890 through the first decade of the present century, Meves (28), McGregor (27), Ballowitz (2), and a number of other skilled observers made notable contributions to our understanding of the metamorphosis Of the germ cells in several vertebrate species. Little has been added in the ensuing years to their remarkably detailed and accurate descriptions of spermatid differentiation in the tailed amphibia. This phase of spermatogenesis has not, however, been as thoroughly investigated in the tailless amphibia. The reproductive physiology of the toad, Bufo arenarum Hensel, has received more attention in recent years than has that of other members of this group. Houssay (21) has studied the hypophyseal control of testicular function. Burgos and Mancini (10) described the normal histology of the testis and the sequence of events in the spermatogenic wave. The meiotic process has been investigated by Saez, Rojas, and De Robertis (32). The present paper records the results of an electron microscope study of the late stages of spermatogenesis in this species. The observations provide new information on the development of the acrosome and head cap; the formation of the perforatorium; the changes in the physical state of the chromatin during spermatid maturation; and the relation of the centrioles to the axial filament and undulating membrane of the tail.