126 Mr Hecipe, Notes on the Proportion of the Sexes in Dogs. 
in the ovum ; but the advent of a spermatozoan may upset all that 
and the sex of the sperm may always dominate that of the ovum. 
According to Castle (p. 199) there is some evidence of this among 
Rotifers, in which eggs under unfavourable conditions which form 
two polar bodies, develope parthenogenetically into males or if 
fertilised become “ winter eggs ” and produce parthenogenetic 
females. In this case the female element in the sperm would 
appear to dominate the male element in the ovum. But there 
are exceptions and the evidence does not appear to me to 
be at all conclusive since we are dealing with eggs capable of 
parthenogenetic development, and there are wide possibilities of 
differentiation in such eggs which are also capable of fertilisation. 
For instance, according to Punnett ( l . c.) fertilisation of arreno- 
tokous females is only possible a few hours after hatching. 
Again, Bateson and Punnett’s interpretation of their studies 
on Poultry ( Report to the Evolution Committee, Royal Society, 
Pt. II., 1905) leads them to infer that sometimes the ovum and 
at others the sperm is responsible for sexual differentiation. 
Thus it may be that for certain species of animals, or for 
certain individuals, the sex of the embryo is derived, from the 
ovum while for others it is derived from the sperm, and that is as 
far as present evidence permits us to go. 
But even if that be so, if the two are necessarily of opposite 
sex, the sex of the ovum has a regular relation to the sex of the 
embryo just as surely as if it conferred its own sex, and for the 
purpose of my future argument this is all it is necessary to 
assume. 
On this assumption a female parent producing ova of one sex 
only will give birth to embryos of one sex, unless the male parent 
possesses no spermatozoa of the opposite sex wherewith to fertilise 
it, in which case the union will be barren. Busing (“ Die Regu- 
lierung des Geschlechtsverhaltnisses bei der Yermehrung der 
Menschen, Tiere, und Pflanzen,” Jena Zeitschr., vol. 17, 1884) 
claimed that the statistical results he obtained from a study of the 
mating of thoroughbred horses, indicated the dominant influence 
of the male parent on the sex of the offspring. Any sire that 
usually produces spermatozoa of one sex only can be fertile, as a 
rule, only with mares which produce ova of the other sex, and to 
such an extent he determines the proportion of the sexes of the 
offspring for which he is responsible ; but where sperm of both 
sexes is uniformly produced, the sire must be fertile with all 
mares producing ova, and, as only one ovum is produced by each 
mare, the responsibility for the sex of the offspring then lies 
solely with the female parent. 
I think it will be found that a very large proportion of the 
evidence adduced to show the preponderating influence of the 
