SYNAPSIS IN THE EGG OF THE WHITE RAT 447 



THE LEPTOTENE STAGE 



The leptotene stage (figs. 8 and 9) which follows the con- 

 traction stage, occurs about five to three and one-half days pre- 

 vious to birth. It may even persist to a later date, as illus- 

 trated by figure 9, from an ovary three days before birth, in 

 which most of the nuclei had passed over into the pachytene 

 stage. The chromatin threads are either regular in outline 

 with a constant size in cross-section or slightly moniliform, ex- 

 ceedingly fine, and very numerous. Many definite visible ends 

 suggest that a large number of individual threads are present. 

 As indicated in figures 8 and 9 the greater part of the threads 

 lie at one side of the nucleus. This arrangement may well be 

 considered as determined by the previous contracted state of 

 the chromatin and as leading to the subsequent polarized orien- 

 tation of the pachytene. In fact, the above figures show a tend- 

 ency for many of the ends of threads to reach the nuclear mem- 

 brane in the region near which the so-called centrosome is found 

 when demonstrable at this stage. In figure 9 are a number of 

 confused clumps of chromatin characteristic of early leptotene 

 nuclei, but no definite chromatin body, uniform in either size or 

 shape could be found at this period. A tendency toward paral- 

 lel arrangement of threads is very apparent in all nuclei closely 

 examined, and in many cases (figs. 8 and 9) figures indicating 

 the side by side approximation of individual threads are clearly 

 demonstrable. Where the moniliform character of the threads is 

 appreciable, the enlargements into which the chromatin is col- 

 lected tend to he exactly opposite to each other in the more closely 

 approximated parallel threads. These leptotene nuclei are not 

 appreciably larger than those of the stages immediately preced- 

 ing. It was not possible to determine the number of individual 

 threads in these nuclei. 



THE SYNAPTENE STAGE 



The synaptene stage may be found from three and one-half 

 to about two days before birth. It often happens that some 

 portions of the threads may show the bipartite nature at a much 

 later period, but, for the most part, do not do so as late as a couple 



