Lnbreeding IgI 
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 
/Avernge 
No. Young 
350 
150 
100 
50 
NIA 
TOA ava y 
el 
Generation 6 10 1 15 
[20] 530) a5 ~~ 40~—S«”y:~« SSCS Tb 
' Ul 
Oct.1002 Jan.1908 Apr.1909Tune 1908 Oct/1903Jan'1904 Apr.1904 June 1904 Oot.1004Jan.i906 Apr.1005 
Fic. 18. 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 otherseries. Theaver- 
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 
