136 Journal New York Entomological Society. [Vol. xxii. 



that which was found being in favor of the males having a shorter 

 egg-larval life than the females but the difference was well within 

 the probable error. 



Table Showing the Number of Individuals Completing their 

 Embryonic Periods in a Given Number of Days. 



Days. Egg-Larval. Pupal. 



2 1 



3 3 



4 92 1,087 



5 1.258 2,398 



6 1,435 438 



7 744 33 



8 40s 9 



9 91 6 



10 14 o 



11 4 2 



In order to pupate the larvae crawl to the dryer portions of the 

 food or even entirely out of it. If pupation occurs in the food 

 the horns of the pupal case nevertheless protrude into the air. The 

 table shows that at first the flies emerge in large numbers but that a 

 few lag along taking more than twice the average time. A sexual 

 difference is more pronounced in the pupal period than in the egg- 

 larval. 7\mong 262 offspring of a single pair the average pupal 

 period of the sisters at 25° C. was 5.0 days and that of the brothers 

 5.3 days. 



The sex ratio varies greatly in different families. Moenkaus^ 

 found 'that among 26,933 individuals there were 1.126 females to each 

 male, but in certain families it is occasionally two to one or even 

 more. It does not change with the age of the parents. The details 

 of the work done upon the modification and inheritance of the sex 

 ratio are too tomplicatcd to be taken up here. 



The newly emerged adults expand their wings as they walk about. 

 In a few minutes they are ready to fly. In this they are almost 

 absolute slaves to light, going in the direction of its greatest intensity. 



1 Moenkhaus, W. J., 191 1, "The Effects of Inbreeding and Selection on 

 the Fertility, Vigor and Sex Ratio of Drosophila ampelophila," Journal of 

 Morphology, XXII, pp. 123-154. 



