BRIDGES 



namely 2X,2A, the female genes out- 

 weigh the male and the result is a fe- 

 male. If we represent the net effective- 

 ness of the female tendency genes in 

 the X by 100, then we should repre- 

 sent the net male effectiveness of a set 

 of autosomes by some lower number; 

 let us say 80. In a 2X,2A individual the 

 ratio of female effectiveness to male 

 effectiveness is 200:160, or 1.25 to 1; 

 and on this formulation the sex index 

 of 1.25 corresponds to the normal fe- 

 male. In the X,2A individual the ratio 

 of female to male effectiveness is 

 100:160; or the sex index of a normal 

 male is 0.63. In the 2X,3A intersex the 

 ratio is 200:240, and the sex index is 

 0.83, which is intermediate between 

 the indices for female and male. In the 

 3N female the ratio is 300:240, and the 

 sex index is 1.25, exactly the same as 

 in the normal female. This identity of 

 sex indices for the 3N and 2N forms 

 corresponds to the observation that 

 there seems to be no strictly sexual 

 differences between them. The larger 

 size, coarser texture of eye, etc., of the 

 3N can be directly attributed to the 

 changed volume of the nucleus, and 

 are not sexual in nature. 



Another type of egg of the 3N 9 is 

 X-l-X+A; and this, fertilized by a 

 normal XA sperm, gives a 3X,2A in- 

 dividual with a sex index of 1.88, 

 which is 50 per cent higher than that 

 of the normal female. This constitu- 

 tion corresponds in fact to the "super- 

 females" that occur in these cultures 

 and elsewhere. The superfemales are 

 much delayed in development, are 

 rarely able to live and are probably 

 completely sterile. 



Conversely, an X-l-A-l-A egg, fer- 

 tilized by the type of sperm that does 

 not carry an X, gives an X,3A zygote 

 with a sex-index of only 0.42. This 

 type of individuals was expected to be 

 more male-like than an ordinary male; 

 and such individuals were looked for 



119 



among the offspring of 3N females. At 

 first none were found; but presently 

 it was discovered that very late in the 

 cultures an occasional example of a 

 distinct type of male occurred. These 

 so-called "supermales" are likewise 

 sterile. Recently, cytological proof has 

 been secured that this type of sex has 

 the constitution X,3A, which agrees 

 with the genetical evidence previously 

 secured. 



It was observed that the intersexes 

 showed considerable variation and 

 seemed to form a bimodal class. And 

 since the cytological investigation had 

 showed that some intersexes had three 

 and others only two of the small round 

 fourth chromosome, it was guessed 

 that the more male-like mode corre- 

 sponded to the full trio of fourth 

 chromosomes, while the more female- 

 like mode corresponded to the cyto- 

 logical type that lacked one fourth 

 chromosome. An effort has been made 

 to secure cytological evidence on this 

 point. But this evidence is inconclusive; 

 as is also that from an attempt to make 

 a genetic test of the number of fourth 

 chromosomes present through use of 

 the fourth-chromosome mutant char- 

 acter eyeless. At present extra fourth 

 chromosomes are being artificially in- 

 serted into the intersexes by continu- 

 ally crossing 3N mothers to males 

 known to have an extra fourth chro- 

 mosome. Contrariwise, in other lines of 

 intersexes, fourth chromosomes are 

 being diminished in numbers by con- 

 tinually mating 3N mothers to males 

 known to lack one of the two fourth 

 chromosomes. Similarly, the superfe- 

 maleness of the 3X,2A individuals 

 might be reduced or be increased by 

 matings with triplo-IV males or with 

 haplo-IV males. For this experiment 

 females are being used whose two 

 X-chromosomes are permanently at- 

 tached to each other (L. V. Morgan 

 '22), and hence that give through non- 



