170 SEX-DETERMINATION [CH. 



are thus two kinds of eggs, one with a complement of 

 chromosomes like that of the spermatozoa, and one in 

 which the idio-chromosome is divided. 



A still clearer case was discovered shortly afterwards 

 (1914) by the writer in the moth Abraxas grossulariata. In 



f^W * 



(0 (*) 



.'" 



(3) (4) 



FIG. 1 9. Chromosomes in the maturation of the eggs of Moths. (Reproduced, 

 by permission of the Editor, from Quart. Journ. Micr. Science, LIX (1914), 

 p. 506.) (i, 2) Pbragmatobia fuliginosa, after SEILER. (i) Outer 

 group of first polar division, 27 ordinary and one large chromosome 

 (total 28). (2) Inner group of same egg, with 27 ordinary and one 

 large chromosome divided (total 29). (3, 4) Abraxas grossulariata, 

 strain which has 55 chromosomes in the female before reduction. 

 (3) Outer group of first polar division, 28 chromosomes. (4) Inner 

 group of same egg, 27 chromosomes. In other eggs the outer group has 

 27, and the inner group, from which the egg-nucleus is produced, 28. 



this species, as in Pbragmatobia, the somatic number is 56 

 in the male, and also in the majority of females, but in a 

 strain which showed peculiar sex-ratios it was found that 

 the females had only 55. The equatorial plates of the second 

 polar division in this strain show clearly that one has 28 



