Recent Advances in the Study of Heredity. 329 
cases of imperfect or potential hermaphroditism by a free admission 
that this may be so. Indeed he would even go further, he says, and 
say that all animals and plants “ are potential hermaphrodites for 
they contain the characters of both sexes." 
We must proceed with great caution here; and before we 
continue with Professor Castle’s theory let us make ourselves as 
clear as we can about the signification of the terms employed. 
A Mendelian hybrid and a hermaphrodite, as the terms are 
commonly understood, are very different things, if we do not confine 
our attention to superficial points of similarity. 
The essential nature of a Mendelian hybrid, as commonly 
understood, may perhaps be best expressed in the statement that 
the only difference between it and a dominant, in those cases where 
the two are externally indistinguishable, is that all the gametes of 
the dominant bear the D factor, whilst only half of the gametes of 
the hybrid bear the D factor, the remainder bearing the R factor. 
This at any rate is what may be called the extreme Mendelian or 
rather Weismann-Mendelian view ; whether it is actually held by 
any Mendelian workers is a question beside the point. This view 
represents the logical conclusion of the Weismannian doctrine that 
the characters of an organism are determined solely by the 
potentialities existing in the germ-cells which gave rise to it. The 
soma is a mere vehicle for the germ-plasm which it protects. It is 
not affected by the characters borne by the germ-cells which it 
contains, any more than these characters are determined by the 
soma in which the germ-cells which bear them are lodged. 
All therefore that we mean, if we hold this view of the 
Mendelian hybrid, when we say that the characters of the recessive 
are latent in the heterozygote is that half of the germ-cells of the 
heterozygote bear the recessive character. 
Now a hermaphrodite is a very different thing from a Mendelian 
hybrid in the sense just explained. An actual, as opposed 
to a potential, hermaphrodite is of course an entirely different thing, 
inasmuch as the characters of both sexes are manifested side by 
side in its soma. But there is almost as profound a difference 
between a potential hermaphrodite and the kind of Mendelian 
hybrid of which we have been speaking. In the hermaphrodite the 
characters of the two sexes are blended in the somatic organization 
of the individual; those of one sex however remain latent. 
The Mendelian view of the nature of the hybrid outlined above 
is probably held most largely by those whose familiarity with these 
