no 



THE AMEBIC AN NATUEAL18T [Vol. XLIX 



his observations, only about 75 per cent, of the eggs of the 

 wild fly ever reach maturity, and in some of the muta- 

 tions no more than 25 per cent, of the eggs develop. 



Another point of interest brought out in the last experi- 

 ment is the fact that the wild, red-eyed fly behaves in 

 exactly the same manner as the mutant pink fly. This 

 may be the reason for the observed shifting of the ratio 

 sometimes in favor of the one variety, sometimes in favor 

 of the other. It shows furthermore that it was not the 

 pink as such that caused the disturbance. The red also 

 might be similarly disturbed and perhaps by the same 

 agent or by another agent that affected the productivity 

 in the same way. 



If the abnormally low number produced by some of the 

 pairs of Table XII be due to the inability of a large num- 

 ber of their eggs to develop, and if we assume this char- 

 acter to be transmissible, it must reappear in the F 2 of a 

 cross in which one of the parents possessed this factor, 

 i. e., a large number of individuals, one quarter of the 

 output, should fail to develop. This would be in accord- 

 ance with Mendelian principles. A number of crosses 

 were therefore made in various combinations with the 

 individuals taken from Table XII. The results follow: 



TABLE XIII 



F 2 of 16 Pairs of a Cross Bed by Pink in Which the Parents Came 

 from AI, al, Table XII, the Average Daily Productivity of 

 Which Was 22 and 20, Eespectively 

 A. Pink $ (Productivity 20 Per Day) X ^ed $ (Prod. 22 Per Day) 



