584 
GEOFFREY SMITH. 
the kind of way in which light is thrown on the constitution 
of sex by breeding experiments. This is by no means the 
only interpretation of the facts that could be offered, but it is 
the simplest and the most in accordance with other results in 
which the phenomenon of spurious alleloTuorphism appears to 
occur. It must be remembered, however, that in cases of 
this kind we ai*e not dealing with the sex characters directly, 
but only through the medium of an assumption which cer- 
tainly gives a simple though not the sole possible explanation 
of the results. 
A similar interpretation is given by Bateson (1) in the case 
of the cinnamon canary and the brown Leghorn fowl. 
Professor Correns (8), on the other hand, as the result of 
hybridisation experiments with Bryonia, comes to the con- 
clusion that in this case the male is heterozygous and the 
female homozygous, and he inclines to give this interpretation 
a wide application both in the animal and plant kingdom. 
In would appear, therefore, that a considerable body of 
evidence is accumulating, drawn from very various fields of 
research, which tends to show the justness of the view that 
in sex we are dealing Avith a phenomenon Avhich may be 
termed “ half-hybridism,” i. e. one sex, either male or female, 
is always a sex-hybrid, while the other is pure. 
We may noAV examine some of the serious difficulties which 
this view encounters. In the first place it may appear very 
strange that the sex-hybrid individual (c? ?) should appear 
in one case as a male and in another as a female, in other 
words that there should be such a complete reversal of 
dominance. But it may be pointed out that dominance is one 
of the least constant phenomena in cases which have yielded 
satisfactorily to Mendelian analysis. Let us, moreover, con- 
sider what happens in the case of functionally hermaphrodite 
animals, in which there can be no doubt at all as to their 
heterozygous nature. We may divide such animals into 
protandrous, simultaneous, and protogynous hermaphrodites, 
of which the first category is by far the commonest. To take 
a typical instance of protandry, in the parasitic Isopoda Epi- 
