SPERMATOGENESIS OF LEPISMA DOMESTICA 389 



35 e and f). Later I believe it fuses with the first, for the latter 

 is seen to increase considerably in size and to show at times a 

 double nature (fig. 35 g and k). 



A third body similar in shape and staining reaction to that 

 seen in the spermatogonia becomes quite prominent at this time 

 (figs. 29 and 30) , due to a slight increase in size and to the appear- 

 ance of a clear transparent area encircling it. Painter ('14) 

 describes in spiders similar small dark-staining spherical bodies, 

 which he calls planosomes and which first make their appearance 

 in the late spireme stage and which he was able to trace through 

 the succeeding divisions. The planosomes, according to him, 

 have spindle fibers, and would therefore be comparable to 

 chromosomes, although as a rule they do not divide, but linger 

 near the middle of the spindle and later go to one side. 



From his description and figures, this body is the same as the 

 one found in Lepisma domestica, only I find it first in the resting 

 stages of the spermatogonia, and have not been able to follow it 

 beyond the prophase stage of the first maturation division. 



The first spermatocyte 



With the condensation of the chromatin segments into the 

 prochromosomes, the nuclear membrane breaks down and two 

 chromosomes located near the periphery are seen joined together 

 by a more or less ribbon-like connection, forming a V-shaped 

 structure. Within or near the arms of the V the plasmosome 

 may be found (figs. 36 and 37). With the exception of the 

 prophase figures in which the idiochromosomes stain more deeply, 

 there is no essential difference in the staining reaction of the 

 idiochromosomes and the autochromosomes; but to make the 

 behavior of the idiochromosomes plain throughout the different 

 stages of the first maturation division, they have been drawn in 

 black, while only the outlines of the autochromosomes are shown 

 (figs. 36, 37, 41, 42, 43, 44, and 45). 



The chromosomes arrange themselves on the spindle and in 

 the metaphase plate (figs. 38, 39, and 40), the sex or idiochromo- 

 somes are still connected and one pair of the chromosomes is a 



