Inbreeding 



191 



have extended from the beginning of the Christian era to the 

 present time. The productiveness of the fertile pairs is shown 

 in the accompanying curve. It will be seen that the productive- 

 ness fell during the winter of 1903, rose during the spring, and cul- 

 minated in the late summer. It fell again during the next au- 

 tumn and winter, but rose again during the next summer. It 

 fell again sharply in the next autumn, but rose rapidly during 



Average 



Ho. Young 



350" 



300 



250 



200 



150 



\ 



100 



50 



\ 



Generation 6 



10 



j 15 ! 20 | 25 30 i 35 40 | 45 50 j 55 j 59 



Oct.l902Jan.l903Apr.l903Junel903 Oct.l903Jan!l904 Apr.1904 June 1904 .6ct.l904.Jan.i905Apr,l9Q& 



FlG. 1 8. Curve of productiveness of fertile pairs of A series of Pomace flies. 

 ( After Castle.) 



the winter and spring, reaching a point much higher than at any 

 previous time, but fell again during the spring. The last rise 

 was connected with a transfer of the flies to a warm chamber. 



This A-series is characterized by low productiveness, and an 

 inclination to sterility, when compared with other series. The aver- 

 age number of young was never as high as 200 until the fifty-third 

 generation, usually it was under 100, and about one in five pairs 

 was sterile. " Control cultures made under identical conditions, 

 but from stock not inbred, had a productiveness two or three 



