770 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



try but of different productiveness, the pairs taken from the more produc- 

 tive brood are invariably more productive, as a glance at Table XX will 

 show. If we weight alike each of the several cases included in Table 

 XX, we obtain the following average values from the lower and higher 

 broods respectively : 



Parental Brood. Filial Brood. 



Lower 196 197 



Higher 232 239 



We get here no evidence of regression. Compare page 741. 



Is a Single Copulation sufficient to fertilize All the Eggs of a Female ? 



It is generally assumed that in many insects a single copulation (or 

 several within a brief period) suffices to fertilize all the eggs subsequently 

 produced by the female. That this is not so in Drosophila is indicated 

 by the following observations. 



In generation M 13, Table II, a female was taken from ajar contain- 

 ing several males and put in a jar with food, where she laid eggs. 

 Pupae were removed from the jar as follows : 



July 



Fresh eggs were found in the jar July 9, and some of these were put 

 into a jar containing some fruit, but none of them hatched. The same 

 day a male was put in with the female, and, as shown above, the eggs 

 laid later were fertile. Likewise a cross-bred female which had been 

 with males for a few days was on June 12 put in a separate jar with 

 food. Pupae were found as follows : 



