often of considerable size, but in Ibla, they
are very minute; they are formed of chitine tunic with underlying
corium, like the rest of the sack; on their crests, there is a row, or a
set of circular groups, or a broad surface, covered, either with minute,
pointed, bead-like bodies mounted on long hair-like footstalks, or with
staff-formed bodies on very short footstalks. I measured some of the
bead-like bodies, in _Lepas anserifera_, and they were 1/2000th of an
inch in diameter, and the footstalks three or four times as long as the
elongated heads. These heads, of whatever shape they may be, have an
opaque, and, I believe, glandular centre; I could not make out with
certainty an aperture at their ends, but, I believe, such exists, and
they seem to secrete a substance, which hardens into a strong membrane,
serving to unite the crest of the fraenum to the edges of the lamellae. In
one case, this bit of membrane seemed formed of a woven mass of threads.
These little glandular bodies, with the membrane formed by them, are
cast off at each exuviation, and new glands formed on the crest of the
fraenum underneath. In some species of Pollicipes, (viz., _P. cornucopia_
and _elegans_,) the fraena, though present and large, are functionless
and destitute of the glands: I believe, they exist in this same
functionless condition, and in rather a different position in the
sessile Cirripedes, and that in this family they serve as Branchiae.

The above-described method by which Cirripedia lay their eggs, namely,
united together in a common membrane, placed between their old outer and
new inner integuments, and the manner in which the lamellae, when thus
formed, are retained for a time fastened to the fraena, and are then cast
off, appears to me very curious. In some of the lower Crustacea, it is
known, that the ova escape by rupturing the ovisacs formed by the
protruded ovarian tubes, and this is the nearest analogy with which I am
acquainted. The ova are impregnated (as I infer from the state of the
vesiculae seminales), when first brought into the sack, and whilst the
membrane of the lamellae is very tender: the long probosciformed penis
seems well adapted for this end. In the male of _Ibla Cumingii_, which
has not a probosciformed penis, the whole flexible body, probably,
performs the function of the penis: in _Scalpellum ornatum_, however,
the spermatozoa must be brought in by the action of the cirri, or of the
currents produced b