102 PAULINE H. DEDERER. 



no odd or " accessory " chromosome, and since there seems to 

 be also no unequal division of chromatin material, there is no 

 element that can be distinguished as an idiochromosome-pair in 

 the metaphase. There is, however, reason to believe that one of 

 the bivalents differs from the others during the growth period in 

 such a way as to indicate that it is to be identified as an equal 

 pair of idiochromosomes, comparable with that described by 

 Wilson in the case of Nezara. 



Ring Stage. 

 Having found twenty-six chromosomes in the spermatogonia, 

 thirteen broken chromatin elements after the spireme stage (Figs. 



17, 18), and thirteen chromosomes in maturation metaphases, I 

 naturally expected to find that in the ring stage resulting after 

 breaking of the spireme, thirteen rings were present. I found, 

 however, only twelve, in a very large number of cells which I 

 examined (Figs. 22—25). No clear case showing thirteen was 

 observed. 



My next step was to study the nucleolus present in the ring 

 stage, to see if it might be different from the earlier double plas- 

 mosome, in containing some chromatin material. I found the 

 double plasmosome, previously noted in Figs. 18 and 19, a-e, 

 and in addition a deep black crescent-shaped band attached 

 around the middle, its concave edge directed always toward the 

 darker portion of the plasmosome as in Figs. 20 and 21, and 19, 

 m, n, 0, the two latter being views of the reverse side of the 

 nucleolus, showing that the chromatin does not completely en- 

 circle the plasmosome. This chromatin band I interpret as 

 equivalent to the two equal idiochromosomes found by Wilson 

 in Nezara, the band thus being bivalent, as is each of the rings, 

 and the number of chromatin elements thus forming the correct 

 reduced number thirteen. 



How, and when, does this chromatin band become associated 

 with the plasmosome ? The evidence seems to show that it is 

 derived from one of the chromatic elements — in the case of Fig. 



18, probably the darker, broader mass — and attaches itself at 

 this stage to the plasmosome. In Fig. 19, /, is represented a 

 plasmosome with the chromatin mass drawn up near it, preparatory 



