SPERMATOGENESIS OF LEPISMA DOMESTICA 385 



One does find cells in quite large numbers at the blind end of 

 the testis, which differ from the ordinary spermatogonia in 

 having large homogeneous nuclei with the chromatin condensed 

 into a single dense mass and irregular in shape (fig. 28). I 

 believe these to be immature Sertoli or nurse cells, for later on 

 one finds such cells, only now they are larger, more elongated, 

 and contain two to four chromatic bodies. Those at the region 

 of the mature spermatozoa are much paler in color and may be 

 wrinkled and twisted upon themselves, indicating perhaps 

 degeneration. 



The spermatogonia occupy a considerable part of the blind 

 end of a tubule of the mature insect during the winter and early 

 spring, and can be easily recognized by their position and by the 

 arrangement of the chromatin in the form of clumps attached 

 to each other by linin threads and grouped around the periphery 

 of the nucleus. This arrangement (fig. 4 is a surface view) is 

 the most common and probably represents a resting condition. 

 Although I have not been able to count these clumps of chro- 

 matin, the number is easily seen to be more than the haploid, 

 and each one probably represents a spermatogonial chromosome. 



The nucleus of the early spermatogonium is quite large and 

 almost equal in size to the nucleus of the growth period. The 

 two or three spermatogonial divisions reduce the nuclear and 

 cell size by apparently not allowing time for growth between 

 divisions (figs. 8 to 11). In prophase the chromosomes are long 

 and bent upon themselves and irregularly scattered throughout 

 the nucleus; later they are drawn into the metaphase plate as 

 shown in figure 5. 



It is only in the larger and therefore the earlier spermatogonia 

 that good counts of the chromosomes can be made. Figure 6 

 shows thirty-four chromosomes in a very clear metaphase plate. 

 The chromosomes are of the curved-rod type, differing con- 

 siderably in size, but close observation fails to show any 

 chromosome or group of chromosomes behaving in any way 

 differently from its neighbors. 



In the telophase of the spermatogonial division the chromatin 

 becomes granular and forms a more or less eccentric ring around 



