624 NATHAN FASTEN 



being parallel to each other. After emerging from synapsis, the 

 threads are much thicker and double in nature. Since no counts 

 can be made, it is impossible to state absolutely whether there 

 are half the number of gemini that there were of leptotene threads, 

 but certainly the number of individual threads is very appreci- 

 ably diminished. This fact, together with the much thicker 

 state of the postsynaptic filaments, strongly indicates para- 

 synapsis. 



2. Summary 



1. The testes of Cambarus virilis and Cambarus immunis are 

 trilobed organs situated in the thorax, below the cardiac chamber. 



2. From the middle of June to the middle of July the testes 

 undergo most rapid proliferation and increase to their maximum 

 size. During this period all the stages in the spermatogenesis 

 may be obtained. 



3. The spermatogonia originate from the germinal epithelium 

 lining the walls of the tubules, and during the early prophase 

 stages the nuclei of the spermatogonia contain two or three large 

 chromatin masses, the karyosomes, from which thin linin strands 

 radiate to the nuclear periphery. By the fragmentation of the 

 karyosomes, the spermatogonial chromosomes originate. 



4. In Cambarus virilis, the spermatogonial number of chromo- 

 somes is two hundred, while in Cambarus immunis, the number 

 is two hundred and eight. 



5. After the spermatogonial divisions the growth period sets 

 in, during which the chromosomes become thread-like, forming 

 thin leptotene rods. No spireme is formed, the rods remaining 

 separate and distinct. 



6. In the synizesis stage these leptotene threads migrate to 

 one pole and arrange themselves in pairs, parallel to each other. 



7. During synapsis, each pair of parallel threads fuses, forming 

 a geminus. Thus the fusion is one of parasynapsis. 



8. In the diplotene (strepsineme) stage the arms of each gemi- 

 nus open up at one end, along the line of their original fusion to 

 form such figures as 8, V and U. 



