Mr Heape, Notes on the Proportion of the Sexes in Dogs. 125 
Again it may be argued that, if both spermatozoan and ovum 
contain both male and female sexual elements, the dominant and 
recessive sex in the offspring would be assured even if an ovum 
was fertilised by a spermatozoan of the same dominant sex. This 
is no doubt true, but in that case it must be assumed that the 
individual resulting from such union would produce sexual 
products of only one dominant sex. 
Such is manifestly not the case and I conclude that, so far as 
this argument is concerned, the probable existence of a dominant 
and recessive sex in both ovum and spermatozoan does not affect 
the question, but that it is essential that an ovum in which one 
sex is dominant should be fertilised by a spermatozoan in which 
the opposite sex is dominant. 
These will be referred to below as male and female ova and 
spermatozoa. 
Whether the sex of the embryo is determined by the ovum or 
by the spermatozoan is another matter. In the case of herm- 
aphrodites it would appear that each of the sexual elements have 
equal power, but where the sexes are differentiated one or the 
other of the generative products must have a determining power. 
In this latter case it may be held that a fight for supremacy 
takes place on the union of each spermatozoan with an ovum and 
that the dominant sex of the embryo is determined by the most 
powerful of the two. 
But on this assumption the 4 sex of the ovum and spermatozoan 
must, as a rule, be supposed to be of more or less equal power, 
and Mendelian laws indicate the certainty that in such case a 
far larger proportion of hermaphrodites would be produced than 
actually occur. 
This appears to me sufficient reason for assuming that, in 
unisexual animals, either the ovum or the spermatozoan has a 
predominating influence, but which of the two is dominant I 
know of no conclusive evidence to show. 
There is a mass of literature dealing with this aspect of the 
problem from a statistical point of view, one portion of it in- 
dicating marked influence of the male, the other no less marked 
influence of the female parent. I will not attempt an exhaustive 
analysis of these statistics here. They deal chiefly with the 
human species and with domesticated animals and are, for the 
most part, open to the objection that they are based only on 
living progeny and disregard those which are still-born or die 
young; for this reason they are not satisfactory for our purpose, 
but at the same time much may be learned from them. 
Doncaster’s and Castle’s works show, it is true, that certain 
parthenogcnetic ova give rise to male and others to female embryos 
and that in this case the power of determining the sex is contained 
