THE INFLUENCE OF THE MALE ON LITTER SIZES . 1 
EDWARD N. WENTWORTH. 
A common belief among practical breeders is that the male 
in multiparous species affects the number at a birth. This be- 
lief has even permeated scientific writing ; many biologists ap- 
parently taking the supposed observation at face value, while 
others have sought biometrical proof in the various accumula- 
tions of the data regarding fertility inheritance found in bio- 
logical records. Thus Ewart reports the case of a long-haired 
Skye terrier bitch that was infertile to two males of her race 
and was the dam of one weakly pup to the service of a third, 
which produced four strong pups to a vigorous West Highland 
terrier. Harris, in some calculations made on litter frequencies 
reported by Wentworth and Aubel, calls attention to the fact 
that there is a statistically significant correlation between the 
size of litter in which boars are produced and the size of litters 
in which their daughters are produced, while he discovers the 
same thing in data reported on Shropshire sheep studied by 
Rietz and Roberts, Several other series of statistics show sim- 
ilar characteristics, although they are not as extensive as those 
discussed. 
From purely logical grounds it is difficult to conceive why 
the male should affect the number per litter. It would seem 
obvious that among the millions of sperm cells in each seminal 
discharge of the male there would be sufficient gametes not only 
to fertilize the relatively few ova released by the female, but 
also to reach them in time to form an effective union. Theoreti- 
cally there seem to be only three ways possible in which there 
might be differences between males. First, the male although 
functional to a certain degree, might produce such weak cells 
that their vitality would be exhausted before they could reach 
the ova. Second, even though they reach the ova, they might 
not form strongly viable zygotes, a condition which is frequently 
found in multiparous animals. Hammond reports that in swine 
there are normally several fertilized ova which atrophy during 
the gestation period, although he seems unable to determine the 
J Paper No. 7 from the Laboratory of Animal Technology, Kansas State 
Agricultural College. 
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