SYNAPSIS IN THE EGG OF THE WHITE RAT 449 



entation of the previous stage is retained, though it becomes more 

 indefinite (figs. 12, 14 and 15). The nuclei sometimes appear 

 more oval, in contrast to the former spherical shape, and the 

 thread is more regularly distributed throughout the entire nu- 

 cleus (fig. 15), with a tendency, perhaps, toward a peripheral ar- 

 rangement. The thread itself is of about the same thickness as 

 that of the preceding stage. It is distinctly monihform, and in 

 early pachytene nuclei it is clear cut and definite in outline (figs. 

 12 and 14). The enlargements of the thread stain heavily and 

 show no evidence of their double origin except in very early 

 threads (fig. 12). In the intervals of the thread between these 

 enlargements, there is a paucity of chromatin, and in some cases 

 it seems entirely wanting, only the linin framework being left. 

 In the later stages of the pachytene nuclei, the outline of the 

 thread becomes less distinct due to the extension laterally of 

 numerous very fine linin strands connecting these enlargements 

 of the thread. 



Figure 13 represents a pole view of a nucleus similar to figure 

 11 or 12 cut through the equator. The threads are accurately 

 drawn as they are seen near the sphere or centrosome. They 

 show no sign of being double and each one undoubtedly repre- 

 sents one end of a loop. They number 40. Consequently there 

 would be 20 loops; and, if each loop represent paired chromo- 

 somes, the diploid number of chromosomes is 40, the haploid 20. 

 Too great reliance, however, must not be put on the number 

 obtained by this single count. 



For the first time in this series of stages, a distinct chromatin 

 body becomes distinguishable in the nucleus (figs. 12 and 15). 

 This chromatin body, however, is constant neither in shape nor in 

 ^ize, and is often distinctly connected with one or more pachy- 

 tene threads. It can hardly be regarded with reason as an 

 accessory or sex chromosome, but is rather to be looked upon as 

 the first appearance of the large chromatin nucleoli which char- 

 acterize the nuclei of the early growth period. 



