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THE AMERICAN NATURALIST [Vol. XL V 



the first cleavage completes the differential division of 

 the bivalent chromosome, instead of dividing it length- 

 wise, the right and left dimorphism is easily understood. 

 Or we might postulate the suppression altogether of the 

 differential oogenetic division of the egg of a white 

 heterozygous, w(y), female of C. philodice which nor- 

 mally results in the separation of color potentials, but it 

 is questionable whether under such conditions the egg 

 would develop. 



Again, the theory of Boveri, 1902, that a gynandro- 

 morph is produced if a spermatozoon (sperm nucleus) 

 unites with one of the two nuclei in the two-cell stage* 

 instead of with the original egg nucleus; or that of 

 Morgan, 1907, that two sperms enter, one uniting with 

 the egg nucleus and (in the bee) determining the female 

 half, while the other gives rise to the male half, may be 

 applied to these dimorphs. According to Boveri 's view, 

 for example, we have to assume in the case of Colias 

 that a "white" sperm from a heterozygous yellow male 

 enters a "yellow" egg containing no sex determiner, 

 and after awaiting the precocious division of the egg 

 nucleus, unites with one of the two nuclei thus produced, 

 and determines the character of the white, or hybrid, 

 half of the resulting female organism. 



7. Precocity of the Males 

 Males of Colias philodice, as in certain other lepi- 

 doptera, not only appear in the fields earlier than the 

 females in the spring, summer, and autumn broods, but 

 also, in every family of this species that I have raised, 

 a very large proportion of males emerge from the 

 chrysalis early in the period during which eclosion takes 

 place. Thus, as shown by Table VII, in brood a. 1909, 

 28 males emerged from the chrysalis at the beginning of 

 the period of eclosion, while only 3 females emerged 

 during the same time, and, of the first half of the brood 

 to pupate, 26 proved to be males and only 5 females. In 

 general, 82 per cent, of the first half of the four broods 

 for which data are here presented to reach the pupal 



