strong light, they can sometimes just be seen whilst the parasite is
attached to the hermaphrodite (the scutum of the latter having been
cleaned on the under side), and are thus represented in fig. 9. They are
formed of thicker membrane than the general integument of the body: the
second segment, or disc, is pointed and hoof-like; when seen in profile
(fig. 11), the upper convex surface has a uniform slope with the upper
surface of the basal segment; it is furnished with a single backward
pointing spine, attached, I believe, on the under side, nearly opposite
the articulation of the ultimate segment: at the apex, there are some
excessively minute hairs or down. The ultimate segment projects
rectangularly outwards as usual, and has on its inner side, rather
beneath the middle, a conspicuous notch (fig. 12), which bears two or
three long, non-plumose spines; on the summit there are three or four
rather shorter spines. On the outside of the great basal segment there
is a single spine curving backwards. The importance of the following
measurements (in fractions of an inch) will hereafter be seen.

Length of whole organ, from end of disc to the further }
margin of the oblique basal articulation } 38-39/6000

Length of whole organ, to the inner margin of the oblique}
basal articulation } 1/6000

Breadth of basal segment, measured half-way between the }
basal and second articulations,--the limb being viewed }
from vertically above } 8/6000

Length of hoof-like disc, measured from the apex to the }
middle of the articulation with the basal segment } 9-10/6000

Breadth of ditto 5/6000

Length of ultimate segment 6/6000

Breadth of ultimate segment beneath the notch 7/20000

Breadth of ultimate segment above the notch 5/20000

I did not see the cement-ducts, which, perhaps, was owing to the corium
extending from the inside of the whole animal some way into the antennae,
thus rendering them rather less transparent than in common Cirripedes.
That the ducts and cement-glands exist, is certain, for the antennae in
every case were enveloped in a little irregular mass or capsule of the
usual, brown, transparent, laminated cement. When several of these
parasites were attached close together, the cement