Mr Heape , Notes on the Proportion of the Sexes in Dogs. 127 
male parent on the sex of the offspring may thus be explained ; 
while statistically the father might be shown to be responsible, 
physiologically the mother controls the governing influence. 
Normally it may be assumed that both sexes of ova and 
spermatozoa are present in the ovary and testis. Among most 
viviparous animals, however, but few ova ripen at one time, in 
many of them only a single one is dehisced ; the necessities 
attending gestation having led to specialisation in this respect. 
On the other hand, having regard to the enormous numbers of 
spermatozoa produced per ovum fertilised, it seems that specialisa- 
tion to the same extent has not occurred in the male and that 
both sexes of spermatozoa are as a rule presented ; thus it follows 
that in these animals, as a rule, the sex of the embryo is solely 
determined by the mother, no matter whether that sex is derived 
from the ovum or the sperm. 
Concerning the proportion of the sexes produced ; it may 
well be that, in those females which shed all their ova the 
proportion of the sexes of these ova and, if they are fertilised, 
the proportion of the sexes of the young so produced, will be 
governed by Mendelian laws. But amongst animals which only 
produce during their life a small proportion of the ova contained 
in the ovary, in which from time to time, owing probably to a 
great variety of circumstances, a considerable number of these 
ovarian ova degenerate and are absorbed, the proportion of the 
sexes of the ova produced is surely directly dependent upon the 
causes which induce the degeneration of some and the ripening 
of other ovarian ova. 
There can be little doubt that the proportion of the sexes 
produced by various species of animals, and by varieties of those 
species, is to some extent a racial characteristic; but from a study 
of the evidence before me I am induced to maintain that such 
proportion may be very largely influenced by a great variety of 
causes which exert their influence upon the male or female 
ovarian ova, causing one or the other to develope and ripen or to 
degenerate as the case may be. The same may be true for the 
testes of the male, but of this I have no evidence. 
A study of the rabbit’s ovary shows that two kinds of 
degeneration prevail, the one affecting first the follicle and 
subsecpiently the ovum, the other first the ovum and subsequently 
the follicle. I have interpreted the latter to mean that the ovum 
is unable to assimilate the nutriment offered to it, while the 
former, I judge, is evidence that, for some reason or other, either 
one or more ova develope at the expense of the others, or the 
nutriment available is insufficient for the maintenance of all 
the ova at that time (“ Ovulation and degeneration of ova in the 
Rabbit,” Proc. Roy. S be., vol. B. 7G, 1905). 
