es:" if the membrane of
these pouches had been specially made adhesive, the analogy would
have been closer.

_Filamentary Appendages._--These have generally been considered to act
as branchiae; they occur at the bases of the first pair of cirri in
Lepas, Alepas, Conchoderma, and in three species of Pollicipes: in
Conchoderma there are similar appendages attached to the pedicels of the
cirri (Pl. IX, fig. 4, _g-k_); and in the above three species of
Pollicipes there is a double row of them on the prosoma: their numbers
differ in different species (in some there being none) of the same
genus, and even in different individuals of the same species; they are
entirely absent in the majority of the genera. These facts would
indicate that they are not of high functional importance; and they seem
so generally occupied by testes (Pl. iv, fig. 5), that I suspect their
function is quite as much to give room for the development of these
glands, as to serve for respiratory purposes. With the exception of the
four above-named genera, the mere surface of the body and of the sack
must be sufficient for respiration: in _Conchoderma aurita_ the two
great expansions of surface, afforded by the folded, tubular, ear-like
projections, aid, as I believe, towards this end.

The shape of the body varies, owing to the greater or less development
of the lower part of the prosoma, the greater or less distance of the
first from the second pair of cirri, and of the mouth from the adductor
scutorum muscle, (Pl. IX, fig. 4, and Pl. IV, 8 _a'_). In all the
genera, the body is much flattened. I may here mention a few particulars
about the muscular system. One of the largest muscular masses is formed
by the adductor scutorum, and by the muscles which surround in a double
layer (the fasciae being oblique to each other) the whole of the upper
part of the prosoma. From under the adductor, a pair of delicate muscles
runs to the basal edge of the labrum, so as to retract the whole mouth,
and two other pair to the integument between the mouth and the adductor,
so as to fold it: again, there are other delicate muscles in some (for
instance in _Lepas Hillii_) if not in all the Lepadidae, crossing each
other in the most singular loops, and serving apparently to fold the
membrane between the occludent edges of the scuta. Within the prosoma
there is a strong adductor muscle, running straight from side to side,
for the purpose, as it appears, of flattening the