but I do not quite understand
the point in question. 6th. "In not having a head or organs of sense;"
this is singularly erroneous: Professor Leidy has shown the existence of
eyes in the mature Cirripede; the antennae, though preserved, certainly
become functionless soon after the last metamorphosis; but there exist
other organs of sense, which I believe serve for smelling and hearing:
and lastly, so far from there being no head, the whole of the Cirripede
externally visible, consists exclusively of the three anterior segments
of the head.

The sub-class, Cirripedia, can be divided into three Orders; the first
of which, mainly characterised by having six pair of thoracic cirri,
includes all common Cirripedes: these latter may be divided into three
families,--the Lepadidae, or pedunculated Cirripedes, the subject of the
present memoir; the Verrucidae containing the single genus Verruca or
Clisia; and, lastly, the Balanidae, which consist of two very distinct
sub-families, the Balaninae and Chthamalinae. Of the other two Orders
above alluded to, one will, I believe, contain the remarkable burrowing
genus Alcippe, lately described by Mr. Hancock, and a second burrowing
genus, or rather family, obtained by me on the coast of South America.
The third Order is highly singular, and differs as much from all other
Cirripedes as does a Lernaea from other crustaceans; it has a suctorial
mouth, but is destitute of an anus; it has not any limbs, and is as
plainly articulated as the larva of a fly; it is entirely naked, without
valves, carapace, or capitulum, and is attached to the Cirripede, in the
sack of which it is parasitic, by _two_ distinct threads, terminating in
the usual larval, prehensile antennae. I intend to call this Cirripede,
Proteolepas. I mention it here for the sake of calling attention to any
parasite at all answering to this description.

NOMENCLATURE OF THE VALVES.

[Illustration: Figure I.

CAPITULUM.]

[Illustration: Figure II.

SCUTUM of LEPAS.]

[Illustration: Figure III.

TERGUM of LEPAS.]

Although the present volume is strictly systematic, I will, under the
general description of the Lepadidae, give a very brief abstract of some
of the most interesting points in their internal anatomy, and in the
metamorphoses of the whole class, which I hope hereafter to treat, with
the necessary illustrations, in detail. I enter on the subject of the
metamorphoses the more readily, as by this means alone c