592 FRANK A. HAYS 
Thus far we have attempted to account for the heavier weights 
and the greater rate of growth of the advanced service litters as 
due entirely to factors other than the nature of the spermatozoa 
and not to any inherited superiority. The effect of such factors 
does not seem adequate to explain the apparent superiority of 
the advanced service litters, therefore there is good evidence that 
a real superiority exists among the advanced service litters as 
compared with the light service litters. The female ancestors in 
both service groups were practically equal in weight. One of the 
15th-service litters represented in chart 9 was sired by Male 
No. 1, the other by No. 3. Two of the four litters combined in 
the 10th-service graph were sired by No. 1 and two by No. 3. 
The smaller weights of the 15th-service litters during the early 
part of the observations cannot for the above reasons be explained 
by male ancestry of different weights. 
One other hypothesis may be proposed to account for the prob- 
able superiority of the advanced service progeny over those from 
very moderate service. Pearl (’17, p. 296) treated both cocks and 
hens with ethyl aleohol, methyl alcohol, and ether at different 
times during the breeding season in order to study the effects 
on their progeny. He found the offspring from treated parents 
in every way superior to those from untreated parents. Pearl 
assumes that alcohol and other poisons act as selective agents 
upon the germ cells of treated animals. It is possible that se- 
lective action might be brought about by heavy sexual service 
of the male. We have previously shown that heavy sexual 
service induces the liberation of sperm which often show no pro- 
gressive motion and are short-lived. Some few of the sperm 
from these advanced services do exhibit the physical properties 
that indicate high vital force. The possibility exists then that 
what few spermatozoa do take part in fertilization are superior 
to the average in the light service groups because the bulk of the 
spermatozoa in the advanced service groups are not equipped to 
take part in fertilization, while this is probably not true in the 
light service groups. Such a hypothesis as the above will thus 
account for the superiority of the advanced service progeny. 
