THE AMEBIC AN NATURALIST [Vol. XLIX 

 TABLE II 



The above are records of mass cultures. When pairs 

 were used, the fluctuations in ratio were much more 

 marked. The records of 40 pairs gave an almost un- 

 broken series running from 1.8:1 up to 6:1. In seven 

 cases out of the 40 (18 per cent.) the pink flies exceeded 

 the expectation; 3 pairs (7.5 per cent.) gave a 3: 1 ratio, 

 while in the remaining 30 pairs (75 per cent.) the pink 

 fell behind. The total number produced by these 40 pairs 

 was 4,056, of which 891 were pink— an average ratio of 

 3.58 : 1, about the same as that shown in Table II. 



In a second experiment the ¥ x hybrids were back- 

 crossed to the pink. The expectation was 1 : 1. But the 

 records of 15 bottles of mass culture showed fluctuations 

 running from 1 : 1 up to 2.3 : 1. The total number counted 

 in these back crosses was 5,527, of which 2,391 were pink, 

 giving an average ratio of 2.31 : 1. The pink flies fell 

 behind again, and in about the same proportion as in the 

 normal cross. 3 



These remarkable fluctuations were observed at the 

 time the experiments were in progress, and it was sug- 

 gested that some environmental condition was responsible 

 for the results by either accelerating or retarding 4 the 

 development of the one or of the other variety. The fact 

 that all these experiments were performed at the same 

 time, and the bottles kept side by side in a room in which 

 a nearly constant temperature was maintained through- 

 out the winter, precludes the chance of a factor outside 

 the culture bottles operating here. Attention was there- 



8 For a detailed account of these experiments see Morgan, 1912. 



generations, the bottles were discarded on the tenth day (counting from the 

 day the first F, emerged) regardless of the number of unhatched pupffi 



