342 
J. A DETLEFSEN AND E. ROBERTS 
summer months of 1916, we made numerous en-masse matings 
in this series to insure keeping the stock ahve. Beginning with 
a single F7 pair of series A showing 1:91 = 1.10 per cent, the 
new series A' was run for nine generations. All generations 
were en-masse matings except Fg and F14, in which paired mat- 
ings were made to ascertain what the crossover values of the 
individual females might be in this line. In the Fg the average 
crossover value for the total population was 8:397 = 2.02 per 
cent. The wide dispersion in this generation does not carry 
TABLE 2 
Series A': derived from series A 
THE DISTRIBUTION OF CROSSOVER 
GENERA- 
TION 
NUMBER 
OF PAIRS 
V.ALUES IN EACH GENiLRATION 
CROSSOVERS 
TOTALS 
CROSSOVER 
VALUES 
1.5 
1 
4.5 
7.5 
1C.5 
13.5 
16.5 
19.5 
Ft 
1 
91 
1 10 
Fg 
X 
1 
86 
1 16 
F9 
18 
u 
2 
1 
1 
s 
397 
2 02 
Fio 
X 
' 

61 
00 
Fn 
X 

133 
00 
F12 
X 
4 
373 
1.07 
Fi3 
X 
9 
1 ,473 
0.61 
Fl4 
251 
25 
10 
2,253 
44 
Fl5 
X 

289 
0.00 
Total 
33 
5,156 
0.64 
^ See text. 
much weight because cultural conditions were poor and fer- 
tihty was low. Pair no. 4, for example, gave 3:15 = 20 per cent, 
but such a pair might well give a much lower crossover value 
with a larger number of offspring. The F^ gave 10:2253 = 0.44 
per cent, and the numbers are large enough to be significant. 
This generation included twenty-five pairs which gave a total of 
2:977 = 0.20 per cent, and an en-masse mating which gave 8:1276 
= 0.63 per cent. There can be no doubt but that an original 
crossover value of 33 per cent has been changed by selection, at 
least, that a marked change has followed selection. For nine 
generations the stock bred true to about per cent crossover. 
The totals for series A' were 33:5156 = 0.64 per cent. 
