124 HEREDITY [CH. 



in this species at least the sex is determined by the 

 egg of the female parent, even before fertilisation. 



Perhaps the most remarkable fact in the whole 

 case remains to be mentioned, that, as far as experi- 

 ment has shown, pure (homozygous) females of the 

 moth A. grossulariata do not exist; all the wild and 

 apparently pure gross, females that have been tested 

 by pairing with lact. males have given lact. female 

 and gross, male offspring, so showing that they are in 

 constitution GL. Since, however, wild males are 

 pure gross. (GG) and since GL females produce 

 (j-bearing male eggs and iy-bearing female eggs, the 

 lact. (L) factor never normally becomes transferred 

 to the male sex. Similar cases have been discovered 

 in the inheritance of pink eyes in Canaries, and more 

 recently for more than one pair of characters in 

 Fowls. Of the latter, the most noteworthy is the 

 barring of the Plymouth Rock, for which all barred 

 hens are found to be heterozygous when mated 

 with an unbarred (black) cock. 



The essential feature of the explanation given 

 above is that eggs of two kinds, male-producing and 

 female-producing, are laid in equal numbers, and that 

 the character for femaleness cannot be associated in 

 the same egg with the gross, factor, so that female- 

 bearing eggs must always bear lact. The case is 

 probably comparable with the 'gametic coupling' 

 which has been found between characters belonging 



