SPERMIOGENESIS OF THE PRIBILOF FUR SEAL 479 



forms, that we may limit the present period in our material. 

 Meves ('99) in his work on the guinea-pig states that the dis- 

 appearance of the 'Manschette' is synchronous with the beginning 

 of the movement of the annulus along the tail filament, a state- 

 ment later confirmed for the rat by Duesberg ('08). The general 

 parallelism of events in the fur seal spermiogenesis with that in 

 other mammals leads us to consider this migration of the annulus 

 down the tail filament as marking the close of the second period. 



Retzius ('09, p. 227), has well pointed out that the term 

 'Manschette' is not a well selected name for a structure around 

 a neck, and that 'Halskragen' is not much better, since both 

 imply an opening at one side, either open or buttoned. As the 

 structure in question is a true tube, he prefers the older name 

 'Schwanzrohre,' which I have adopted in this description in the 

 translated form 'caudal tube.' 



The cytoplasmic body of the spermatid at the beginning of 

 this period is still more or less polygonal in section, with the 

 nucleus more or less shifted proximally from its central position. 

 During this stage the whole cell becomes elongated in a direction 

 radial to the tubule, and the nucleus approaches the proximal 

 end of the cell until it reaches the surface, the cytoplasm being 

 massed toward the lumen while the cell membrane and acrosome 

 cover the apical portion of the nucleus. At the beginning of 

 this period the manschette or caudal tube appears, one of the 

 most striking phenomena observed in mammalian spermiogenesis. 

 The riddle of its origin and fate has interested some of the most 

 prominent workers in cytology. A brief review of the literature 

 will be given at the close of the present paper, while the descrip- 

 tion of personal observations will be alone presented here. 



Shortly after the centrosomes and their tail filament have 

 reached the nuclear membrane there appears in the cytoplasm 

 surrounding the axial thread a series of delicate filaments attached 

 to the nuclear membrane. The proximal ends of these arise in 

 a circle around the basal end of the nucleus with the centrosomes 

 as a center, while their distal ends project freely into the cyto- 

 plasm in directions at various angles to the axial thread which 

 they surround (figs. 16 to 19). The first form of the caudal 



