SPERMATOGENESIS 143 



where tail sheaths are present these are formed from the chromo- 

 2)hobie material (Figs. 64, 65, E-G). No satisfactory explanation 

 of the evolutions of the Nebenkern has been given as yet. 



The tail filament arises from the peripheral centriole at the end 

 of the second spermatocyte division, just at the commencement 

 of the formation of the acrosome (Figs. 63-66, D). As they reach 

 the posterior position the two centrioles come to lie side by side, and 

 the tail filament grows very greatly in length (Figs. 63-66, E, G). 



Two other structures demand attention. Firstly the post-nuclear 

 bodies which originate in an unknown way appear as small 

 granules, staining in osmic in the late spermatocyte (Fig. 66, A). 

 They are usually very near to the Golgi apparatus. An excellent 

 account of their behaviour was given by Gatenby and Wigoder in 

 1929 (40). In the spermatid they have come to lie just behind 

 the nucleus and far from the Golgi complex, which is by this time 

 depositing the acrosome at the tip (Fig. 66, D, E). They are known 

 in mammals, amphibians, molluscs, insects and annelids, and in 

 all cases they expand until they form a strongly argentophil band 

 at the posterior end of the elongating nucleus. This may be very 

 large, as in the case of Cavia cohaya (Fig. 66, G). 



The origin of these post-nuclear bodies is doubtful. Its first 

 observed a^Dpearance by the Golgi apparatus, as also its ability 

 to be stained by osmium and silver, suggests an origin from the 

 Golgi apparatus, but its definite formation has not yet been seen. 

 Gatenby and Wigoder attribute a supporting function for the 

 delicate tail to it, and this it probably would have, but there is no 

 evidence for this other than its position, and it has not been 

 demonstrated that the body is any more rigid than the surround- 

 ing cytoplasm. 



Finally we come to the recently-described vacuolar system. 

 For a description of this system in spermatogenesis we are again 

 indebted to Gatenby (35). He has described its behaviour in 

 Abraxas, Helix and Cavia. An account of this system in the 

 spermatogenesis of Saccocirrus was also given by him much earlier 

 before its identity was known (33). 



In Helix the vacuoles stainable intra vitam in neutral red are 

 found at first in the spermatocyte within the Golgi apparatus 



