Fig. 1, Larva of Lepas in the second stage of development; _a_,
supposed antennæ (second pair); _m_, mouth; _c_, three
pairs of legs. (Copied from Burmeister's 'Naturgeschichte
der Rankenfüsser,' Tab. 1, fig. 3.)
2, _Lepas australis_: pupa or larva (2 _a_, of natural size) in
the last stage of development, with the young cirripede in
its natural position, obscurely seen within,--the specimen
having been treated with caustic potash, _and so rendered
transparent_,--viewed laterally and greatly enlarged.
Scarcely more than the outline of the shell or carapace is
represented. The darkly shaded part to the left represents
the extent of the sack of the pupa, or the cavity occupied
by the thorax, with its limbs.
_a_, both antennæ, adhering by their discs to a piece of wood.
_b_, dorsal surface of the shell or carapace; and immediately
underneath this letter is the point of reflection of the
membrane investing the thorax, so as to line the sack of
the pupa.
_b′_, is the posterior end of the animal, and of the orifice
on the ventral surface, through which the legs are
protruded.
_c_, six pairs of natatory legs.
_d_, pair of caudal appendages, seated on a minute abdomen.
_m_, mouth, from which the œsophagus can be seen running into
the stomach, the latter having two dark cæca; the stomach
sweeps round in the pupa to the abdomen, near _b′_; but in
the young included cirripede, only as far as the letter
(_b_), where the bases of the posterior pair of cirri and
the anus lie.
_n_, apodemes, supporting the eyes, produced deeply inwards
from the eye-bearing segment (N, in fig. 4) of the antennæ.
_s_, bottom of sack of the young cirripede immediately after
its metamorphosis; it extends as far as _s′_. (See _s_, in
fig. 3.)
_t_, gut-formed cement-gland (or incipient ovaria), seen on
the near side of the animal, whence a cement-duct, _t′_,
runs into the near antenna.
_u_, internal and anterior part of the pupa, filled with
pulpy, oily matter, together with the incipient muscles of
the peduncle; when stretched out it forms the peduncle of
the young cirripede. See _u′_, in fig. 3.
_x_, bases of the pedicels of the cirri of the young included
cirripede.
2 _a_, Pupa of _Lepas australis_ of natural average size,
within a half-inch wide.
3, Young cirripede (on a smaller scale than Fig. 2),
immediately after the exuviation of the bivalve-like
pupal carapace, the basal segments of the antennæ, the
eye-apodemes and eyes. The young cirripede has just assumed
its proper position at nearly right angles to what it held
whilst packed within the pupa,--this change of position
having been effected by the opening out or stretching of
the deep fold of membrane (see _n_, in fig. 2) formed
over the eye-apodemes and eyes, previous to the act of
exuviation.
_a_, the three terminal segments of the antennæ of the pupa,
still remaining cemented, in the same position as before,
to the same piece of wood: the basal, or eye-bearing
segment (N, in fig. 4), has been moulted with the pupal
carapace.
_c_, _d_, legs and caudal appendages of the pupa, not as yet
moulted, but quite functionless; the external membrane of
the thorax, and that lining the sack of the pupa, are,
likewise, as yet retained, but soon will be cast off.
_s_, bottom of the sack of the young cirripede, which can now
be easily distinguished.
_u′_, the peduncle.
_x_, _y_, _z_, primordial valves, composed of chitine: _x_,
being the scutum; _y_, the tergum; _z_, the carina.
3 _a_, small portion of one of the primordial, non-calcified
valves, much magnified.
4, ventral surface of pupa; on the same scale, and in the same
semi-transparent condition as in fig. 2.
_a_, antennæ.
_b_, limit of sack on the sides in the ventral or lower half
of the pupa.
_b′_, posterior end of the carapace.
_c_, _d_, bristles of the natatory legs and of the caudal
appendages, protruded through the orifice of the carapace.
_e_, orifice of the acoustic sacks.
_m_, mouth, with the œsophagus attached to it, obscurely seen
through the carapace; the stomach having been removed.
_n_, apodemes supporting the eyes.
N, the eye-bearing or basal segments of the antennæ.
_o_, the second or main segment of the antennæ.
_p_, the third or disc segment of the antennæ.
_v_, the fourth or terminal segment of the antennæ.
W, ventral surface, bordered by the edges of the carapace;
the letter stands near the extremity of the œsophagus.
5, First pair of natatory legs: _f_, lower segment of pedicel;
_g_, upper segment of pedicel; _h_, lower segment of ramus;
_i_, upper segment of ramus; _k_, outer ramus; _l_, inner
ramus of same leg; _r_, sternal surface between the first
and second pairs of legs, with singular thickened ridges
and folds.
6, Abdomen with two caudal appendages: ^1, first abdominal
segment, attached to the posterior thoracic segment; ^2,
second abdominal segment; ^3, third or last abdominal
segment; _h_, lower segment; _i_, upper segment of caudal
appendage.
7, Transverse section of the pupa, close to the eye-apodemes;
these being made to stand more upright than in fig. 2. The
internal organs of the animal have all been removed.
_a a a′_, section of carapace; from _a_ to _a′_, on the lower
side, forms the ventral surface, with three longitudinal
furrows, here in some degree opened out.
_c_, crest of thick membrane on each side, forming the sides
of the lateral furrows.
N, the posterior margin of the eye-bearing segment (see fig.
4) of the antennæ; the edges of which are hardened and
thickened, and are produced inwards, forming
_n_, the apodemes, to which are attached the (_n′_) great
compound eyes.
8, Terminal portion of an antenna, greatly magnified, seen
from above.
_o_, part of the second or main segment; an oblique line
shows a line of separation of the upper thinner and lower
thicker membrane; _o′_, single spine borne at this segment.
_p_, disc-segment, bearing seven spines; _p′_, an irregular
border of the cement-tissue, believed to have debouched
through the spoke-like minute tubes seen on the disc.
_v_, terminal segment, projecting almost rectangularly
outwards; _v′_, most delicate tube or ribbon, believed to
consist of cement-tissue.