136 
GENETICS: T. ELLINGER 
Proc. N. A. S. 
records are taken from the Danish herd book Vols. V and VII. All these 
sows have been kept in state-supervised breeding centres under uniform 
conditions and care. They have all farrowed the first time at about one 
year of age and from then on been bred regularly producing ca. 2 1 /* 
litter per year, practically without regard to season. The successive litters 
will for that reason be highly correlated with age, but it seems most con- 
venient to use the litter-number as unit. The average of all litters, being 
11.5 pigs, is far above the average shown by swine of the American type, 
and although these 134 sows undoubtedly are selected group, the great 
fertility is one of the outstanding and valuable qualities of the breed. 
3- 
2. 
I 
I 13456789 10 
LITTER NUMBER 
FIG 1. 
The dots indicate the actual found averages for litter-size in the first ten litters. 
The curve is fitted to these valves. 
In the second column of table 1 the average sizes of the successive ten 
litters are given. 
table i 
LITTER NO. AVERAGE SIZE OP LITTER THEORETICAL SIZE OF LITTER 
1 9.45 9.25 
2 10.01 10.42 
3 11.50 11.24 
4 12.01 11.81 
5 11.99 12.19 
6 12.16 12.38 
7 12.13 12.39 
8 12.34 12.24 
9 11.90 11.92 
10 11.66 11.43 
Average 11.52 11.53 
Plotting the series of average values over a base indicating the suc- 
cessive generations (fig. 1) we see that they show an increase in fertility 
