382 



P. W. WHITING. 



or fourteenth day of adult life and then decreases. No consistent 

 change in type of deficiency according to mother's age could be 

 detected. 



Possible explanations of this rise and subsequent fall of ratio of 

 deficient during life of mother may be considered. 



Cytoplasm or yolk of eggs might differ according to some 

 rhythm in the life of the female. The influence would have to be 

 carried through the larval period and up to the time of the 

 formation of the organs in the pupa. 



Something in the food of the larva might vary according to the 

 age of the mother, some ingredient of the fluid injected at time of 

 stinging the caterpillars. 



Neither of these theories involves genetic change in maternal 

 contribution. 



A third explanation may be suggested. It has been shown that 

 linkage in Drosophila varies with age of mother. If this is true in 

 Habrobracon a difference in genetic composition of offspring 

 according to the mother's age may be brought about. In order 

 to test this possibility records on a lethal factor linked with orange 

 were reinvestigated (Whiting, P. W., 1921) and the five fra- 

 ternities involving linkage were summarized according to vials. 

 Results are given in Table E. The difference between vials a and 



TABLE E. 



CROSS-OVERS OF A LETHAL LINKED WITH ORANGE ARRANGED ACCORDING TO 



AGE OF MOTHER. 



b is of no significance. There is an increase in cross-overs from 

 b to c, 13.5 4.6 per cent., which is probably significant and a 

 decrease after c, 16.1 5.0 per cent, which is also probably 

 significant. If this rise and fall of crossing-over according to age 

 is proved when further linked factors are found, it may be the 

 most reasonable explanation of change in ratio of deficient. 



