354 



ROSCOE R. HYDE 



of 31 per cent. Table 1 shows that in the case of the Woods Hole 

 stock the fertility gradually fell throughout the year. I fully 

 expected to find that the fertility would be continually reduced on 

 inbreeding, and yet the fertility of the stock rose in August and 

 September until it was actually higher than it was during the 

 September of the previous year by 6.3 per cent. The meaning of 

 this is obscure. It will be recalled that Castle found seasonal 

 fluctuations in productivity in his flies. The period, however, in 

 which low productiveness prevailed in his stocks corresponds in a 

 general way with the period of high fertility in my stocks. 



In the light of this evidence it would seem that inbreeding as 

 such cannot be the vera causa of the low fertility that usually 

 accompanies the process. It would seem from this evidence and 

 the evidence presented by Moenkhaus that the fertility of a stock 

 could be maintained, and the closest inbreeding practiced, provided 



TABLE 4 



Showing the fertility of the Woods Hole, white-eyed, inbred, I2 and I3 stocks. lA = 

 Woods Hole stock; 2A = white-eyed stock; 3A = I3 stock; 4A = h stock; 5A = 

 inbred stock, F26 generation 



