SPERMATOGENESIS OF THE BLACK-CLAWED CRAB. 28 1 



(Fig. 8). Within its nucleus may be seen numerous irregular 

 chromatin clumps distributed along a meshwork of thin strands. 

 A single centrosome can also be distinguished. 



When the primary spermatocyte begins its process of develop- 

 ment, the first noticeable change occurs in the nucleus. The 

 chromatin clumps fragment (Figs. 13 and 14) and soon weave 

 out into a large number of leptotene threads (Fig. 15). These 

 threads are distinct but so numerous that it was impossible to 

 get any count of them. 



The next step in the growth process is the pre-synaptic stage 

 (Fig. 1 6) in which the leptotene threads wander to one pole of 

 the nucleus and become lined up side by side into pairs. Within 

 the cytoplasm a single, spherical chromatoid body makes its 

 appearance and it is invariably surrounded by a clear area. This 

 is quite similar to the bodies found by Wilson ('13), Komai ('20) 

 and myself ('14, '18 and '24) for other forms. In slides which 

 were considerably destained the chromatoid body took on a 

 lighter hue than the chromatin of the nucleus. I found this 

 same differentiation in destained preparations of Cancer productus 

 Randall, Cancer oregonensis (Dana) Rathbun, and Cancer gracilis 

 Dana which were fixed with Flemming's strong solution. From 

 this stage on the chromatoid body persists and can be easily 

 distinguished. 



The pachytene stage follows (Fig. 17) in which synapsis of the 

 paired leptotene threads takes place thereby transforming them 

 into distinct gemini. In many of the preparations the line of 

 fusion between some of the leptotene threads could be clearly 

 seen. This is similar to the condition found in Cambarus mrilis 

 (Fasten '14), but differs from that found in the various Cancer 

 crabs studied (Fasten, '18 and '24) where the fusion between the 

 leptotene threads is complete. 



The diplotene and post-diplotene stages (Figs. 18 and 19) 

 follow each other in logical sequence. In the diplotene stage 

 the paired threads of each geminus open up at one end along the 

 longitudinal plane of fusion but remain attached at the opposite 

 end, thereby producing figures like V, 8 and U. At the same 

 time a second longitudinal furrow occurs along each of the 

 opened arms, thus converting each geminus into four thin strands 



