s
something in this locality hostile to the development of the parasitic
males. I have noticed only one instance (that given in fig. 9) in which
the males were imbedded a little way apart; generally they touch each
other, and are cemented together: where there are several males, they
occur at different levels, as measured from the under or upper surface
of the chitine border: in one instance of four males adhering to one
valve, I distinctly perceived that the lowest one was white, pulpy, and
recently attached; the two above, which were placed close together and
between the same laminae of chitine, were mature; and the third still
higher up, was dead, empty, transparent, and half decayed: in some other
instances, I have found the uppermost parasites dead, and, together with
the surrounding chitine, partially worn away.

[53] I am greatly indebted to Mr. Peach for his unwearied
kindness in procuring me fresh specimens. Mr. W. Thompson allowed
me to dissect one, possessing particular interest, out of his
three Irish specimens. Professor Forbes procured me a specimen
from the Shetland Islands, and Professor Steenstrup was so kind
to take pains to send me some Scandinavian specimens.

The larva of the male must have a different instinct from the larva of
the hermaphrodite; for the latter attaches itself head downwards to a
coralline, whilst the male larva crawling on the scuta of the
hermaphrodite, discovers, I presume by eye-sight, the fold in the shell
beneath the translucent border of chitine, and there invariably attaches
itself. Its object in choosing this particular spot, I believe, simply
is that the depth or thickness of the chitine is there greater, and
sufficient for its imbedment, which would hardly be the case elsewhere.
This parasite has, as we have seen, no mouth or stomach, and indeed,
considering its fixed position and the non-prehensile condition of its
limbs or cirri, a mouth would have been of no service to it, without it
had been extraordinarily elongated. The male must live on the
nourishment acquired during its locomotive larval condition; and its
life no doubt is short, but yet not very short, as I infer from the
depth to which mature specimens are buried in the chitine border. The
full development of the spermatozoa consumes, I suppose, some
considerable lapse of time. The thorax and limbs, though furnished with
muscles, are obviously, as already remarked, of no use for prehension;