10 



DEVELOPMENT OF THE FROG'S EGG 



[Cn. I 



Rath, and we must suspend judgment until further work throws 

 more light upon the question. 



The spermatogenesis of the frog has not been worked out in 

 the same detail as that of the salamander, yet vom Rath ('95) 

 has made certain important statements in regard to it. The 

 prophase of the mitoses, before the ripening period, has in the 

 frog a close resemblance to the skein-stage of the heterotypic 

 and homoeotypic variations in the salamander. But, on the 

 other hand, in the metakinetic stage the peculiarities of the 

 homoeotypic and heterotypic forms, as described by Flemming, 



B 



FIG. 6. Stages in the last maturation-division of sperm-cells of Frog. 

 (After vom Rath.) (Figs. C, D, F slightly modified.) 



are absent. The formation of the chromatin-rings and tetrad- 

 groups in the frog (Fig. 6, A, B, C) differs from that of the sala- 

 mander and is much more like that of Gryllotalpa. The rings, 

 owing to the strong contraction of the segments, are relatively 

 small in the frog, but proportionately thick (Fig. 6, B). From 

 each ring arise the four spherical chromosomes of each tetrad- 

 group (Fig. 6, C). The ring-stage lasts quite long in Rana, 

 judging from the frequency of its presence. The rings lie at 

 the periphery of the nucleus. 



