118 The Spermatogenesis of Desmognatlius Fusca 



the spermatid. Fig. 34 is a transection of the expanding nucleus of 

 the spermatid, showing the arms of the Vs cut across, while Fig. 35 

 shows the fully formed spermatid. That the nucleus of the spermatid 

 undergoes a slight enlargement before the period of transformation into 

 the spermatozoon is evident. 



The determination of the exact method in which the spindle is estab- 

 lished in the spermatocyte of the second order has been attended with 

 considerable difficulty, and despite careful work with many specimens 

 well fixed and stained, it has been im_possible to arrive at an absolute 

 decision. The spindle is established from a stage similar to that shown 

 in Fig. 27. One centrosome lies at an extreme side of the cell-body 

 directly under the cell-membrane, and from it there extends a radiation 

 of fibers. The other centrosome lies close to the nuclear membrane 

 some distance from the first, and it likewise is the center of radiations. 

 The spindle seems to be formed by the fusion of these two sets of 

 radiations. The earlier history of the formation of the achromatic 

 figure is not so clear. The identity of the centrosome at the end of the 

 first mitosis is lost, as has already been stated, so that centrosomic con- 

 tinuity between the first and second divisions has not been established; 

 nor has it been shown that the two centrosomes of the second division 

 were derived from a single centrosome, which presumably would have 

 been one of the daughter-centrosom_es of the previous division. Fig. 25 

 suggests that this is the case, and that my failure to trace them has been 

 due to the fact that one of them moved close to the nuclear membrane 

 and on that account and because of the absence of well-marked radia- 

 tions became in most cases indistinguishable. The entire achromatic 

 figure, in comparison with the one of the previous division, is weak. 

 A centrosphere is lacking, radiations are not well marked, and the 

 astral shield at the end of the division is not developed. 



From an examination of the Amphibian literature, it appears that 

 there are no figures showing the development of the spindle in the 

 second division. McGregor failed to trace the continuity of the centro- 

 some in the spermatocyte divisions of Antphiuma, though Meves, in his 

 description, leaves no doubt as to his interpretation of centrosomic con- 

 tinuity. Eisen, in Batrachoseps, describes and figures the spindle in the 

 second division as formed by a fusion of two sets of radiations (fiber- 

 cones) resembling somewhat the method described above as the one 

 believed to occur in Desmognatlius. In his work, new-formation of 

 centrosomes (archosomes) is assumed to occur. His fiber-cone resembles 

 closely one of the centrosomes in Desmognatlius, surrounded by its radia- 

 tions, and undoubtedly the two are the same. 



