e._--I examined these in the larvae presently to be
mentioned, and therefore they were in better condition than in the
mature animal when cemented. Their total length, measured along the
outside, from the basal articulation to the end of the disc, is
32/6000ths or 33/6000ths of an inch--that is, one third longer than in
_I. Cumingii_; whilst the hoof-like disc itself is 8/6000ths, or only
1/6000th of an inch longer than this same part in _I. Cumingii_: the
apex of the disc is downy, or bears some excessively minute spines. The
ultimate segment has its end irregularly rounded, with the spines
obscurely divided into two groups, the outer group consisting of two or
three longer and thinner spines, and the inner group of, as I believe,
five rather shorter spines: the longer spines equal in length the whole
ultimate segment. I could not perceive that they were plumose, as in
many other genera. A single, rather thicker and long spine, pointing
backwards, is attached to the under side of the disc, nearly opposite to
the point where the ultimate segment is articulated on the upper convex
surface. Another single, curved spine is attached on the outer side of
the basal segment, near its distal end.

_Development of the Male._--In the specimen before alluded to, which
included two males, one of these was only the 30/1000ths of an inch in
length, and therefore between one fifth and one sixth of the size of the
mature male. It had, probably, undergone only one exuviation since its
metamorphosis, for the larva is nearly as long, namely, 25/1000ths of an
inch. In this young male, the mouth formed one third of the entire
length: it was attached, not as in every other case to the sack of the
hermaphrodite, but low down to the peduncle of the other male.

In the sack with these two males, there were certainly four, I believe
five, larvae, which in every main point of structure resembled the larvae
of other pedunculated Cirripedes. From the peculiar form of their
prehensile antennae, differing in no respect, except in the proportional
lengths of the segments, from the same organ in the male _I. Cumingii_,
I can feel no doubt that these were the larvae of the male _I.
quadrivalvis_;--for a moment's reflection will show how excessively
improbable it is, that several larvae of some other Cirripede, and that a
Cirripede intimately allied to the parasitic male Ibla, should have
forced themselves, without any apparent object, into the sack of t