388 HARRY H. CHARLTON 



of filaments certainly is reduced and each one becomes much 

 thicker. The threads now loosen up and occupy practically 

 all the cell, the space between the nuclear membrane and the 

 cell wall being quite small (fig. 24, Wilson ('12), stage f). I 

 have not been able to find the longitudinal splitting of the thread 

 — a process which Wilson ('12) describes as taking place. 



There follows a period when it is hard to distinguish the threads 

 as such (fig. 29, Wilson ('12), stage g). Wilson calls it a net-like 

 arrangement. The actual breaking of the threads or pachytene 

 stage is not well exemplified in Lepisma, but stage g is soon 

 followed by the clumping of the chromatin into masses irregular 

 in shape and joined together by linin threads (fig. 30). By a 

 further condensation of these masses we get the prochromosomes. 

 The formation of tetrads showing the quadrivalent condition 

 of the autochromosomes is never apparent, neither is there any 

 split indicating a parasynapsis. 



The idiochromosomes retain their form and staining reaction 

 until the formation of the delicate filaments (stage d), when 

 they break up and form threads which are darker in color than 

 the other threads, and one may be seen in close relation to a 

 small plasmosome (fig. 35 a). The idiochromosome threads are 

 at first very long and may extend across the entire width of the 

 cell. They appear somewhat beaded, just as is the case with 

 the threads of the autochromosomes. 



During the later periods the threads show an end-to-end appo- 

 sition, being joined by very fine linin fibers (fig. 35 m). The 

 threads now become shorter and thicker assuming the U shape 

 followed by the definite formation of loops with the plasmosome 

 between them (figs. 20 and 35 j). Figures 35 i and h would 

 seem to indicate that the limbs of the loop come together and 

 become still more compact to form clumps lying against the 

 nuclear membrane with the plasmosome still lying between 

 them. For a considerable time the idiochromosome threads 

 show a very clear inequality in that the thread nearest to the 

 plasmosome is the longer (fig. 35 k) . 



A second small plasmosome may be formed and lies to one 

 side with no attachment to either idiochromosome thread (fig. 



