No. 583] ROLE OF ENVIRONMENT IN DROSOPHILA 417 



tions where a more exact comparison between a cross and 

 its reciprocal could be made. In the autumn of 1913 

 I went over the ground again with this object in view. It 

 was found that the F t females heterozygous for abnor- 

 mality are just as likely to be abnormal when their ab- 

 normal factor comes from the father as when it comes 

 from the mother. The extent to which the abnormality 

 is realized depends on the condition of the food. This in 

 turn will depend in part not only on its amount but to 

 what extent it is worked over by the larva which again 

 depends, in large part, on the number of eggs laid by the 

 female. To this extent and only in this sense does the 

 condition of the mother affect the condition of her daugh- 

 ters. If the females lay too many eggs for the amount 

 of food that is present, crowding results and the daughters 

 show abnormality to a less degree than when fewer eggs 

 are laid (that hatch) and little competition takes place. 

 Now the normal female is more likely to lay more fertile 

 eggs than the abnormal female. Hence other things be- 

 ing equal the heterozygous daughter of a normal mother 

 is more likely to be normal than the heterozygous daugh- 

 ters of an abnormal female (which are therefore again 

 more like their mother — very abnormal in this case, be- 

 cause the former mother is more likely to lay more eggs 

 than the latter). The relation between the two cases is 

 therefore not owing to the egg transmitting abnormality 

 to the daughters better than the sperm, but to the number 

 of eggs likely to be laid by the mother in question. 



In order to examine further whether when abnormality 

 comes in with the egg it is more likely to be shown in the 

 F x heterozygote, a number of parallel experiments were 

 made, of which the following are samples : 



GRAY Red Abn. $ BY Wild £ Gray Red Abx. by Wild $. 



(1) Very abn. J 1 and (1) Fairly abn. $. 



(2) Normal (a few slightly ab- (2) Most fairly, a few very abn. 



(4) Normal' (a few slightly ab- (6) N? (40) 1 slight abn. $. 



normal). 

 (3) Normal (a few slightly ab- 

 normal). 



(3) Most fairly, a few very abn. 

 , 4 ) Slightly abn. 

 ,:.) Slightly abn. 



(7) N$. 



