character is a loss of these appendages. The absence of the male character
therefore necessarily involves a development of these appendages, and
there is not much more reason for saying that the male under the influence
of the parasite develops female characters, than for saying that the male
character is absent. There is no evidence in the facts concerning
parasitic castration for Geoffrey Smith's conclusion that the female
characters are latent in the male, but the male characters not latent in
the female: both return to a condition in which they resemble each other,
and the primitive form from which they were differentiated.

By his studies of parasitic castration Geoffrey Smith was led to formulate
a theory for the explanation of somatic sex-characters different from that
of hormones. He found that in the normal female crab the blood contained
fatty substances which were absorbed by the ovaries for the production of
the yolk of the ova. When _Sacculina_ is present these substances are
absorbed by the parasite; the ovary is deprived of them, and therefore
atrophies. In the male the parasite requires similar substances, and its
demand on the blood of the host stimulates the secretion of such
substances, so that the whole metabolism is altered and assimilated to
that of the female. It is this physiological change which causes the
development of female secondary characters. He describes this change as
the production of a hermaphrodite sexual formative substance, on the
ground that in at least one case eggs were found in the testis of a male
_Inachus_ which had been the host of a _Sacculina_, but had recovered. It
must however be noted that the _Sacculina_ itself is hermaphrodite, with
ovaries much larger than the testes. It is possible that while the
parasite prevents the development of testis or ovary in the host, it gives
up to the body of the host a hormone from its own ovaries which tends to
develop the female secondary characters: for the parasite is itself a
Crustacean, and therefore the hormone from its ovaries would not be of too