308 EDMUND B. WILSON. 



Turning now to the spermatogonia, we find an accurate cor- 

 relation between the spermatogonial chromosome-groups and 

 those of the maturation divisions. In all cases there are 18 equally 

 paired larger chromosomes, an unequal pair of idiochromosomes 

 and a very small pair of ///-chromosomes ; and these 22 alone 

 are present in the individuals of Type B (Fig. I, d\ In those 

 of Type A an jf-chromosome is present in addition, making 23 

 in all (Fig. I, a}. In three of the five males of this type, as 

 stated above, the .y-chromosome is no larger than the ///-chro- 

 mosomes, and the spermatogonia correspondingly show 20 large 

 and three very small chromosomes. In the remaining two indi- 

 viduals of this type the ^-chromosome is considerably larger than 

 the ///-chromosomes, both in the maturation-divisions and in the 

 spermatogonia. The spermatogonia of these individuals seem 

 therefore, at first sight, to show 21 large chromosomes and two 

 small. In Type B, which have but 22 chromosomes, the first 

 maturation-division shows but 12 chromosomes, the second II ; 

 and only two classes of spermatozoa are formed, which corre- 

 spond to Classes 2 and 4 of Type A. 



The foregoing data, when compared with the conditions found 

 in the female, give a decisive result regarding the relation of 

 these chromosomes to sex-production. If the unpaired 5-chro- 

 mosome were of the same nature as the odd or " accessory " 

 chromosome of other coreids we should expect to find one such 

 chromosome in the male and two in the female ; and since males 

 and females alike possess in addition two small ///-chromosomes 

 the males should show three small chromosomes and the females 

 four. Such however is not the case. In both sexes there are 

 individuals that possess three small chromosomes (Fig. I, a, I, 

 c] and others that possess but two (Fig. I, d, I,./). Evidently 

 therefore the ^-chromosome is indifferent as regards the sex- 

 characters. On the other hand, close study of the larger chro- 

 mosomes shows the same relations as those observed in other 

 forms that possess unequal idiochromosomes. In the female 

 groups all are equally paired. In the male all are thus paired 

 save two, one of which is evidently the small idiochromosome. 1 



1 This fact is not always readily made out, since the small idiochromosome is not 

 very markedly smaller than the others ; hut I am sure of the observation, and the 

 fact was determined in many spermatogonial groups long before I suspected the 

 presence of a pair of idiochromosomes in this genus. 



