A Monograph on the Sub-class Cirripedia (Volume 2 of 2) / The Balanidæ, (or Sessile Cirripedes); the Verrucidæ, etc., etc.

PLATE 30.
LARVÆ OF LEPAS: SECOND AND LAST STAGES OF DEVELOPMENT.

• 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.