346 ROSCOE R. HYDE 



This evidence taken by itself does not prove conclusively that 

 the loss in productivity was due to a decrease in the fertilizing 

 power of the gametes. That this is a very probable interpre- 

 tation however is shown by the fact that in the F^ generation 

 when the productivity dropped to 159 per pair their fertility was 

 only 32 per cent. And yet the flies of the F^ generation were 

 producing twice as many fertile sperm and twice as many fertile 

 eggs as shown by outcrossing into the truncate stock (Part II, 

 diagram E). 



3. lo and I3 stocks 



In the fifth generation of the inbred stock, when they were 

 producing 184 offspring to the fertile pair, I set aside two dif- 

 ferent bottles besides a number of pairs that were kept to con- 

 tinue the inbred stock. All of these flies had descended from 

 the same grandparents, a single pair of the third generation. In 

 one bottle there were three females and four males. This I shall 

 designate as I2. In the other bottle there were ten males and 

 twenty- two females. This I shall refer to as I3. These flies were 

 set apart April 2, 1912, and received no attention except that the 

 flies were transferred to clean bottles about every three weeks and 

 fresh food added from time to time. It is important to bear in 

 mind that we have three stocks descended from the same germ- 

 plasm. 



4. The white-eyed stock 



This stock arose as a mutation from the inbred stock early in 

 the history of the strain. This stock received the same treatment 

 as I2 and I3. 



5. The pink-eyed stock 



This is an eye mutation that arose in one of Morgan's cultures.^ 

 It had been bred for some three years. I received my stock from 

 Mr. Liff, a graduate student in the department, who has made a 

 study of their productivity. This stock was bred in mass culture 

 for about four months when the present experiments were carried 

 out. 



^ Science, vol. 33. 



