Fig. 6, Proteolepas bivincta: diagram, showing the probable
position of the young animal, just before its
metamorphosis, within the carapace of the supposed pupa;
_a_, caudal appendages; _b_, six pairs of natatory thoracic
legs; _c_, mouth, no doubt closed and functionless, as in
other pupæ; _g_, threads of attachment, with cement-ducts
in process of formation; _h_, antennæ.
7, Proteolepas bivincta, magnified about twenty-six times.
_m_, mouth, the summit being formed of the labrum and palpi
joined.
_^{1}c_, first segment of body; homologically the seventh or
last cephalic segment.
_^{2}t_ to _^{8}t_, second to eighth segment of body;
homologically, first to seventh thoracic segments.
_^{9}a_ to _^{11}a_, ninth to eleventh segment of body;
homologically, three segments of abdomen.
_d′_, three muscles attached on each side to the labrum, and
running to the gnathites.
_e e_, great ovarian sack.
_f_, true ovaria.
_g_, threads of attachment.
_h_, three terminal segments of the antennæ of the pupa.
_i_, vesicula seminalis.
_k_, papilla representing the penis.
Fig. 1, _Balanus tintinnabulum_: an enlarged longitudinal section
through the shell and sack, with the right-hand scutum and
tergum and right-hand half of shell and basis removed,
exhibiting the body of the animal not in section. The cirri
are exhibited only on one side.
A, A, orifice of shell, within which lies the operculum
formed by a pair of scuta (S), and pair of terga (T).
B, basis (homologically the anterior end of the shell).
K, carina of shell (or dorsal valve or compartment of shell).
K′, sheath of carina.
L, lateral compartment of shell. The carino-lateral
compartment is hidden by the scutum and tergum.
R, rostrum of shell (or ventral valve or compartment of
shell).
R′, sheath of rostrum.
O, O, opercular membrane, connecting the opercular valves
with the overhanging basal edge of the sheath.
S, scutum.
T, tergum.
_a_, adductor scutorum muscle, with the scutum on the near
side removed.
_b_, the whole space enclosed by a broken sinuous line, round
_a_ and _b_, shows the cut surface of attachment to the
near scutum, which has been removed.
_b′_, lower muscle, on the near side, running from near the
basal edge of the scutum to near the basal margin of the
labrum (_e_). Above this are three other muscles (all on
the near side), running to the membrane between the labrum
and adductor muscle.
_c_, prosoma, including the main portion of the stomach and
thickened ends of the vesiculæ seminales: homologically
this is formed by the development of the second thoracic
segment, which carries the first pair of cirri; and
possibly, in part, by the antecedent segment, _i. e._ the
first thoracic segment.
_c′_, thorax, extending from the prosoma to the posterior
end of the body: the letter (_c′_) stands on the segment
supporting the third cirrus; homologically, this segment is
the fourth thoracic.
_d′_, orifice of the acoustic sack, above which is the basal
articulation of the first cirrus.
_e_, labrum, forming the back (_i. e._ anterior end) of the
mouth, with the transverse palpi obscurely seen on the
summit.
_f_, sack in which the animal lies, with the tunic lining
it, continuous with that investing the prosoma (_c_), and
lining the under sides of both opercular valves, but cut
off round (_b_) and (_a_) by the removal of the near
scutum. The branchia on the further side, which occupies
the position represented at fig. 3, is covered by the body
of the animal.
_g g_, ovarian, inosculating cæca, branching from the simple
duct (of which the near one of the pair is represented),
leading to the ovaria (not represented) within the body.
_h_, rostral depressor muscle of the scutum: the lateral
depressor muscle of the scutum is hidden by the body and by
the membranes of the sack.
_i_, carinal depressor muscle of the tergum.
_z_, antennæ (three terminal segments) of the pupa; I
distinctly saw these in this species, but they are here
represented considerably too large, even on the supposition
that a young shell had been drawn, and magnified about
twelve times.
2, Testes of _Balanus perforatus_, greatly magnified.
3, Branchia of _Bal. tintinnabulum_, on the same scale as in
fig. 1, and in its natural position. This drawing was made
by lifting up the body in fig. 1; the organ being thus
completely exposed over its whole interior surface; _a_ is
the basal end of the spur of the tergum.