SEX AND GENES 209 



together, they produce barred and black males and 

 females as 1:1:1:1. 



A similar mechanism is found in moths, where the cyto- 

 logical evidence is more certain. When a female of the 

 darker mid ty]De variety of the currant moth (Abraxas) 

 is mated to a lighter mutant type, the daughters have a 





a 



•' I- 





^ i^ 



X 



Fig. 122. 

 a, Kediiced group of cliromosomes of the egg of Fumea casta; b 

 and 6' outer and inner pole of the first maturation division of the 

 egg; the single X-chromosome is present only at one pole. (After 

 Seiler.) 



