330 
A . D. Darbishire. 
ideas is only derived from text-books. But there is another view, which 
probably more closely resembles that held by experts, and which comes 
much closer to the conception of a sexual hermaphrodite. 1 have 
already said, in an earlier lecture, that the formula DR may relate 
either to the nature and proportion of the kinds of germ-cells borne 
by a zygote ; or to the somatic organization of the zygote itself. 
The former alternative corresponds to the Mendelian view which 
we discussed first; the latter to the view which as I have said 
approaches more closely the conception of a sexual hermaphrodite. 
This second view is involved in the idea that every zygote is a 
double structure, as opposed to the gamete which is a single one. 
According to this view, the statement that the recessive 
character is latent in the heterozygote means not only that half of 
its germ-cells bear the recessive characters ; but that the recessive 
character actually exists potentially in the somatic organization of 
the heterozygote itself. It is important to bear these two Mendelian 
views of the nature of the hybrid (and indeed of the zygote in 
general) distinctly in mind, because our interpretation of certain 
phenomena of sex ( e.g ., the appearance of rudimentary structures 
characteristic of the opposite sex) will be determined by the form 
of Mendelian theory we start with. 
To return to Castle’s theory. He assumed that every individual 
in a dioecious species was a sex hybrid and produced $ and 5 germ- 
cells in equal numbers. The result of the union of any large 
number of ova and spermatozoa at random would therefore be as 
follows:— 
S + 2 (ova). 
$ + 2 (spermatozoa). 
1 <? $ : 2 2 : 1 2 2 (zygotes). 
Now Castle supposes that pure sex zygotes of the type $ $ 
and 2 2 do not exist, and supports this supposition by analogical 
reasoning. The only fertile unions of gametes are, therefore, those 
between ova and spermatozoa bearing dissimilar sexes. All zygotes 
are therefore heterozygotes as regards sex : they are the result of the 
union of dissimilar gametes; and the gametes which they produce are 
of the same two kinds. The principle of alternative dominance has 
to be invoked to explain the fact that these sex-heterozygotes may 
be either “ males ” or “ females.” And herein lies the chief 
weakness of the theory ; the production of the two sexes in approxi¬ 
mately equal numbers receives a most unsatisfactory explanation. 
The theory which has superseded Castle’s and seems in much 
