No. 533] INHERITANCE IN COLIAS PHILODICE 281 



stage were males, only 18 per cent, females. The re- 

 maining individuals of these four families, constituting 

 the second half of each in reaching the pupal stage, were, 

 on the other hand, largely females (66 per cent.), only 

 34 per cent, being males. 



These facts led me to entertain the idea that the eggs 

 which are to become males may be laid before the female- 

 producing ova. To test this hypothesis, I segregated 

 the successive batches of eggs laid by seven females in 

 1910, and reared the larva? of each successive batch 

 separately, to see if the lots laid first by each female 

 would contain a larger proportion of males than those 

 laid later. It will be seen from Table VII that in fam- 

 ilies b, c, d and e there was in each case a slightly larger 

 proportion of male eggs in the first laying than in the 

 batches laid subsequently, but in families g, i and k ex- 

 actly the reverse is true, the last lots of eggs laid by each 

 female (viz., 3g and 4g, 2i, and 3k and 4k) containing 

 more males than females. It is evident, therefore, that 

 the male-producing ova are not laid on the average 

 earlier than those that are female-producing, but that 

 the larval period of the male is shorter than that of the 

 female. 



In consequence of this fact it is not surprising to find 

 that when a brood of caterpillars is exposed to any ad- 

 verse conditions such as starvation, an excess of male 

 butterflies, as Mrs. Treat long ago found, will result, for 

 the simple reason that many females, exposed to adverse 

 conditions during a longer period of growth than that of 

 the males, have been eliminated, while the more pre- 

 cocious male caterpillars survive in greater numbers. 

 This will explain, I believe, the excess of males in my 

 cultures, 507, or 55 per cent, of the total number being 

 males, 412, or 45 per cent, being females. There is no 

 evidence, however, of any differential death rate be- 

 tween the yellow and the white females. Neither is more 

 precocious in larval development than the other, and 

 intestinal diseases appear to strike each with equal viru- 

 lence. 



