SPERMIOGENESIS OF THE PRIBILOF FUR SEAL 487 . 



cytoplasm, in which numerous granules may be distinguished, 

 but containing no regular spiral fiber. Outside of this and form- 

 ing the external sheath of the connecting piece is the involucrum 

 externum, which, as we have seen, is made up of the wall of the 

 caudal tube plus the cell membrane of the spermatid covering 

 this portion. The connecting piece is terminated by the annulus, 

 or distal half of the posterior centrosome. In the adult sperm 

 it stains but slightly and is very inconspicuous, but in favorable 

 cases may be made out as a narrow transverse disc, pierced in 

 the center by the axial filament. In figures 33 and 36 there 

 still remains a small amount of cytoplasm, c.r., attached to the 

 connecting piece, but this soon disappears. In the same prep- 

 aration in which the spermatozoon represented in figure 33 was 

 found there were many others in which the outline of the con- 

 necting piece was perfectly cyhndrical, this particular one having 

 been selected for other reasons. ^ 



Pars -principalis. The main, or*principal piece of the tail 

 (fig. 33, m.p.) consists of the tapering axial filament, covered by 

 a homogeneous sheath, and extends from the annulus to the 

 point where the naked axial filament continues alone beyond the 

 sheath surrounding it. The diameter of the principal piece grad- 

 ually decreases throughout its whole extent, so that it is difficult 

 to determine the exact point at which the sheath stops and the 

 final segment of the tail begins in every instance. 



Pars terminalis. The end piece (fig. 33, e.p.) of the fur seal 

 spermatozoon is short, measuring approximately 2.5 n in length. 

 It appears to be made up of the single axial filament alone. In 

 many instances it appeared to be broken, and the limitations of 

 the material at hand prevented any satisfactory study of this 

 extremely delicate object. 



GENERAL DISCUSSION 



No attempt will be made here to review the voluminous liter- 

 ature upon spermiogenesis, since so many masterly summaries, 

 such as those of Meves ('99 '01), Waldeyer ('06) and Duesberg 

 ('08), already exist and make it entirely unnecessary. The rela- 

 tion of certain points as brought out in the fur seal spermiogenesis 

 should be here emphasized, however. 



