rectum is of unparalleled length, and
extremely narrow; it can be best detected after the dissolution by
caustic potash of the softer parts, when its inner coat of chitine can
be seen to be continuous, in the ordinary manner, with the outer
integuments of the thorax. The anus, as already stated, is seated on a
slight swelling, and consists of a small longitudinal slit (_f_, fig.
2), placed close outside the two very minute caudal appendages.

_Organ of Sight._--In all the specimens, a little below the fold
separating the mouth from the peduncle, and near the abdominal (or
rostral) edge, a black ball (_c_, fig. 1), about 1/1000th of an inch in
diameter, is conspicuous. When dissected out, it is somewhat conical in
form, and appears to consist of an outer coat, with a layer of
pigment-cells of a dark purple colour, surrounding a transparent, rather
hard lens, apparently leaving a circular orifice at the summit, and
forming a short tube at the base, surrounding what I believe to be a
nerve. I was not able to perceive that this eye consisted of two eyes
united, which the analogy of other Cirripedes makes me suppose probable,
although in the ordinary and hermaphrodite _Ibla quadrivalvis_, the eye
also appeared single. It is seated under the two transparent muscular
layers, close upon the upper end of the stomach, and this is the exact
position, as stated in the introductory discussion (p. 49), in which the
eyes of pedunculated Cirripedes are commonly situated.

_Generative System._--Within the muscular layer all round the upper part
of the peduncle, and surrounding the stomach, there are numerous,
little, rather irregular globular balls, with brown granular centres, so
closely resembling the testes in other Cirripedes, though of smaller
size, that I cannot doubt that this is their nature: they were much
plainer, larger, and more numerous in some specimens than in others. The
vesiculae seminales can seldom be made distinctly out; but having cut
one specimen transversely across the thorax, they were as plain as could
be desired, lying parallel and close to each other above the rectum,
(the animal being in the position as drawn,) and therefore in their
normal situation. Each had a diameter four times as great as that of the
rectum. In this individual the contents seemed (whether from
decomposition or state of development, or from my not having used high
enough power, I know not,) merely pulpy; but I have since found, in
anothe