532 Theophilus s. Painter, 



it lies on the side of the nucleus next to the observer. The most 

 important point to note is that the planosome does not show any 

 association for the accessory chromosomes at this time. 



Synizesis. The synaptic contraction is marked and con- 

 stitutes a very conspicuous stage in the tufted variety. The lepto- 

 tene-threads are drawn completely to one side of the nuclear cavity 

 and form there a densely staining mass, as is shown in Figs. 49 

 and 50. It has not been possible to follow the course of the indi- 

 vidual leptotene- threads at this time or during the extreme contrac- 

 tion phase. 



In the cell shown in Fig. 50, we find two deeply staining 

 masses lying among the contracting leptotene-threads marked "J-". 

 These are the accessory chromosome elements. Lying near the edge 

 of the nuclear cavity we have a small but very densely-staining 

 body, marked „P". This body is the planosome which we found 

 earlier in the leptotene stage. 



The behavior of the supernumerary chromosome is very inter- 

 esting. The position shown in Fig. 50, is not altogether typical, 

 as the body may lie anywhere in the nuclear cavity. In some cells 

 it lies on the edge of the mass of threads where it is always easily 

 seen because of its great affinity for the stain and its sharp outline. 

 At other times it lies entirely free in the space left by the 

 contracting threads. The essential point of interest is the fact 

 that the planosome shows no affinity foi- the accessory chromosome 

 at this time. The importance of this behavior will be pointed out 

 later. 



Our interest in the pachytene stage centers again in the hétéro- 

 chromosome elements. The accessory chromosome appears much as it 

 did in the gray variety, either as two rods lying side by side or 

 else as one general mass. The planosome, on the other hand, always 

 lies free in the nuclear cavity, as shown in Fig. 51 P. 



The planosome in the majority of cases appears as a single 

 body, but cells have been found in which the larger body has 

 apparently broken up into s wo smaller parts. Observations on this 

 point are difficult because it is hard to say with certainty that the 

 second small body is not the outer end of a pachytene-thread. If 

 this breaking up of the planosome really does take place, it would 

 seem to indicate that we are dealing liere with a bivalent body. 



'JMie question of what proportion of the pachytene cells carries 

 the planosome is a very improtant one. In slides where the extrac- 



