464 BENJAMIN H. PRATT AND J. A. LONG, 



blocks peripherally arranged, and in none of the three forms 

 described by these authors is there that finely graded series of 

 nuclei showing the fragmentation of these blocks and the simul- 

 taneous appearance of linin threads. In the case of the rat, the 

 contraction stage certainly must start earher than in these other 

 forms. It would seem Irom the figures that this stage persists 

 longer in the rabbit and in man (von Winiwarter, '00). 



It has already been mentioned that distribution of nuclei in 

 zones — the most advanced stages being in the interior and the 

 least advanced at the periphery with the intervening stages in 

 more or less definite concentric areas — is almost completely 

 lacking in the case of the rat. It would seem that this phenome- 

 non might be correlated with the comparatively shorter period 

 over which these nuclear changes extend in this form. 



In the case of the cat (von Winiwarter and Sainmont, '08) 

 there is a clearly defined chromatin element, fairly constant in 

 appearance, persisting throughout this entire series of changes. 

 There is certainly no such body in the case of the rat; and von 

 Winiwarter finds none in either the rabbit or man. In all 

 other respects, particularly in reference to the gross as well as 

 the more detailed appearance of the chromatin threads through- 

 out the entire series of changes, the four forms are closely 

 similar. 



Of particular interest throughout this study has been the 

 relation of the chromatin to the linin threads, and of the chroma- 

 tin nucleoli of the later periods to the synaptene and diplotene 

 threads. During the first part of the series of stages here de- 

 scribed, the evidence is very strongly in favor of the conception 

 that fragmentation of the original chromatin blocks and migra- 

 tion of these chromatin fragments along the hnin threads then 

 evident, contribute largely to the formation of the leptotene 

 threads. This process is almost exactly reversed at the other 

 end of the process of synapsis. The chromatin nucleoli seem to 

 be merely the closely compacted clumps of that same chromatin 

 which has now migrated back along linin threads to one or more 

 common points. The contact of the synaptene and diplotene 

 threads with these chromatin bodies, and the persisting linin 



