margin (_b_), is generally marked
by a slight notch. The dimensions and proportions vary much: the longest
specimen, including the imbedded portion, was 8/100th, and the shortest
barely 5/100ths of an inch in length; the width of the widest portion
varied from 1 to 2/100ths of an inch: the specimen figured (Pl. IV, fig.
8 _a'_, and Pl. V, fig. 1,) is a broad, short individual. Generally, the
middle of the peduncle is rather wider than the upper part.

_Peduncle._--The main part of the animal, as may be seen in the drawing,
consists of the peduncle, of which the imbedded portion tapers more or
less suddenly in a very variable manner, and is of variable length,--in
one specimen being one fourth of the entire length, and in another
consisting of a mere minute blunt point. The free upper part of the
animal is bent in various directions, in relation to the imbedded
portion. The latter passes obliquely through the chitine membrane and
corium, lining the sack of the female, and running along amidst the
underlying muscles and inosculating fibrous tissue, is attached to them
by cement at the extremity. The peduncle is often, but not in the
individual represented, much constricted at the point where it passes
through the skin of the female, and generally at several other points,
especially towards the extremity (see fig. 1); the stages of its deeper
and deeper imbedment being thus marked. The constrictions are, I
believe, simply due to the continued growth of the male, whilst the hole
through the membrane of the female does not yield. The imbedment, which
is considerable only when the lower part of the peduncle is almost
parallel to the coats of the sack, seems caused by the growth and
repeated exuviations of the female; I believe, that the larva attaches
itself to the chitine tunic of the sack, and that the cement, by some
unknown means, affects the underlying corium, so that this particular
portion of the tunic is not moulted with the adjoining integuments, and
that the growth of the surrounding parts subsequently causes this
portion to be buried deeper and deeper: it is, I believe, in the same
way as the end of the peduncle in _Conchoderma aurita_, sometimes
becomes imbedded in the skin of the whale to which it is attached.

The outer tunic of the peduncle is thin and structureless: in the fold
(fig. 1 _h_) under the cirri, there is a central triangular gusset of
still thinner membrane, corresponding in position to the membra