35 ORILLA STOTLER WERNER. 



would show the dominant sex-linked character and half would 

 show the recessive character, the female inheriting it in each case 

 from the male parent of the FI generation. 



According to this scheme it might be supposed that in the case 

 , of the Indian runner duck each autosome sustains a balanced 

 condition of the male and female-tendency genes. The Z- 

 chromosomes might be thought of as carrying a preponderance of 

 male-tendency genes. An individual, then, receiving two Z's 

 would become a male. The two W's might be thought of as 

 carrying female tendency genes only. These, however, would be 

 thought of as being quantitatively greater than the male ten- 

 dency genes carried in a single Z and an individual receiving a 

 Ww plus one Z would become a female. 



A large number of animals belong to the X-Y type in sex- 

 determination. In these the female has an even number of 

 chromosomes, the X-chromosome being paired or diploid. The 

 male has one less than the even number of chromosomes found in 

 the female, the X being unpaired. This gives the female more 

 chromatin than the male. In a few of the animals of the WZ 

 mechanism, such as some of the moths, the male has an even 

 number of chromosomes. The female has the odd number and 

 one less than the male which would give the male more chromatin 

 than the female. But in most of the cases in the moths the female 

 has one more chromosome than the male, the male having the 

 even number. 



In the birds, if my observations are borne out on other species, 

 it would seem that the female has the preponderance of chromatin. 

 If the conditions in the duck are representative of that which 

 one might expect to find generally in the aves, we would expect 

 in the moths which are likewise digametic in the female, that the 

 true state of affairs would be like those moths in which the 

 female has one more chromosome than the male. The difference 

 between the two types of animals, the XX-XY and the WZ-ZZ, 

 is essentially in the matter of which sex produces the two sorts of 

 gametes. And so far as this mechanism is concerned it is a 

 matter of indifference which sex produces the two sorts of gam- 

 etes. The important thing seems to be that one sex, usually the 

 female, should have more chromatin than the other. 



