Studies on Chromosomes 



171 



In the ensuing division, if the supernumerary hes free it passes 

 without division as a heterotropic chromosome to one pole (8, u). 

 When connected vs^ith the idiochromosome bivalent it passes to one 

 pole attached to one or the other of the idiochromosomes (Fig. 

 8, k-m, p-t). In either case one pole receives 1 1 chromosomes and 

 one 12 (Fig. 8, e, f); but since the supernumerary may accompany 

 either idiochromosome four classes of spermatid nuclei are formed, 

 namely: 



(l) 10= 7=11 (2) I0+/+i=I2 



(3) 10+;- II (4) 10 + 7 + i = 12 



As described in an earher paper ('07a), there is a tendency for 

 the supernumerary to be associated more often with the small 

 idiochromosome than with the large, and classes i and 2 are accord- 

 ingly more numerous than 3 and 4. I was formerly inclined to 

 attribute importance to this as pointing to the more frequent 

 occurrence of the supernumerary in the male than in the female. 

 The larger series of data now available leads me to doubt whether 

 it has much significance; for if (leaving the 21-chromosome forms 

 out of account) the whole series of forms be taken together, one 

 or more supernumeraries are found in 27 out of 34 males, and in 

 15 out of 19 females — about 80 per cent in each case. It appears 

 therefore that in the long run the supernumeraries are distributed 

 between the two sexes with approximate equality. 



Figs. 7, q-s show spermatogonial groups from individuals with 

 one large supernumerary, but in none of them can this chromosome 

 or the small idiochromosome be certainly distinguished. Fig. 

 7, t-y are from individuals with one small supernumerary, each 

 showing three very small chromosomes. In t and u the small 

 idiochromosome is doubtful. Fig. 7, v-y, on the other hand, are 

 from an individual (terminalis. No. 2), showing great numbers of 

 very fine spermatogonial groups, in almost all of which the small 

 idiochromosome is at once recognizable. The same is true of a 

 second individual from the same locality. These two individuals, 

 from the Paulmier collection, were the first material I examined 

 and found so puzzling until the examination of another similar 

 individual, No. 43, cleared up the nature of the second division. 



