122 Mr Heape, Notes on the Proportion of the Sexes in Dogs. 
moment at which the sex of the offspring can be determined is 
the time of fertilisation, and that no influence exerted sub- 
sequently can alter that sex. 
If these statements be true therefore, it follows that all this 
portion of the literature may be disregarded from the point of 
view from which it was written ; at the same time it appears to 
me to be of considerable value from another point of view and 
well worthy of attention. 
The most recent writers on the subject claim that the sex 
of the generative products is governed by the laws of heredity, 
and, so far as I understand, the effect of extraneous influences on 
the sex of the progeny is wholly denied by them. 
I find reason myself to believe, that while each ovum and 
spermatozoan in the generative glands contains within itself sex, 
which is probably determined by the laws of heredity, that the 
proportion of those male and female ova and spermatozoa which 
are developed and set free from the generative glands may be 
regulated by selective action, exerted in accordance with the 
resultant of a variety of extraneous forces. If this be true the 
proportion of living male and female ova and spermatozoa which 
are freed from the generative glands, and the proportion of the 
sexes of the offspring which result therefrom, will thus be 
influenced. It is this aspect of the problem with which I 
specially deal in the following paper; and it is in this connection 
that I find the literature, referred to above, of interest. 
The very existence of sex demands that ova and spermatozoa 
or both should be themselves sexual, i.e. male, female, or 
hermaphrodite. 
Recent researches by Wilson {Journ. Exp. Zool. vol. 8, 1906) de- 
monstrate that the spermatozoa examined by him are histological^ 
differentiated into two groups and it appears not improbable 
that these groups are male and female. If this be so, although 
histological evidence is wanting, there is no prima facie reason 
why ova should not be similarly differentiated, and the power 
some females possess to produce parthenogenetically in some cases 
functional males, in others functional females, points emphatically 
to that conclusion. 
In this relation the research of Doncaster “on the maturation 
of the unfertilised egg and the fate of the polar bodies in the 
Tenth redinidae” {Quart. Journ. of Mic. Sci., vol. 49, 1906) regarding 
the product of conjugation of certain portions of the divided polar 
bodies in parthenogenetic eggs, is of great interest, and is strongly 
suggestive, to my mind, that the ovum, in all animals, is capable 
of determining the sex of the progeny. 
Apart from this latter point, to which I will refer below, it 
may I think be assumed that what is true for the spermatozoa 
