SPERMIOGENESIS OF THE PRIBILOF FUR SEAL 489 



tube is seldom present after the annulus has begun its migration 

 along the axial filament, and suggests that its possible function 

 may be that of a protection to the centrosomal apparatus, shut- 

 ting out the mitochondria from that region until the differen- 

 tiation of the annulus and the other centrosomal structures may 

 be completed. No such explanation is adequate for the fur seal, 

 since the caudal tube may be readily followed from its first 

 appearance up to its final incorporation in the connecting piece 

 as a peripheral layer, or sheath. In this instance it forms a 

 permanent structure in the adult spermatozoon, a fate in harmony 

 with the second view, held by Klein ('80) Biondi ('85), Hermann 

 ('89), C. Niessing ('96), Lenhossek ('98), and Van Molle ('06). 



The function of the rodlet which grows out from the proximal 

 centriole is here as elsewhere unsatisfactory. It appears to act 

 mechanically during the shifting and shrinkage of the caudal 

 tube, as shown in figures 29 to 32, but what advantage this may 

 be is not evident, nor is it at all probable that this is its only 

 function. Shortly after this stage it disappears completely. No 

 trace can be observed of its being utihzed in the formation of 

 the spiral filament of the connecting piece, contrary to the opinion 



of Van Molle ('06). 



The behavior of the centrioles follows the general plan appar- 

 ently common to all mammals, being simpler than that described 

 by Meves ('09) for the guinea-pig, and agreeing closely with that 

 seen by Retzius ('09). The proximal centriole of the sperma- 

 tid divides into two portions, closely adherent to the nuclear 

 wall, each connected by a filament to one of the distal group. 

 The distal centriole divides into an anterior and a posterior por- 

 tion. The posterior portion becomes the annulus, while the 

 anterior one divides again, forming the Noduli posteriores. These 

 changes may be graphically expressed by diagram 1. 



