Metamorphoses; larva, first stage, [pp. 9-12]; larva, second stage, [p. 13]; larva, last stage, [p. 14]; its carapace, [ib.]; acoustic organs, [p. 15]; antennæ, [ib.]; eyes, [p. 16]; mouth, [p. 17]; thorax and limbs, [p. 18]; abdomen, [p. 19]; viscera, [ib.]; immature cirripede, [p. 20]; homologies of parts, [p. 25.]
Description of mature Lepadidæ, [p. 28]; capitulum, [ib.]; peduncle, [p. 31]; attachment, [p. 33]; filamentary appendages, [p. 38]; shape of body, and muscular system, [p. 39]; mouth, [ib.]; cirri, [p. 42]; caudal appendages, [p. 43]; alimentary canal, [44]; circulatory system, [p. 46]; nervous system, [ib.]; eyes, [p. 49]; olfactory organs, [p. 52]; acoustic(?) organs, [p. 53]; male sexual organs, [p. 55]; female organs, [p. 56]; ovigerous lamellæ, [p. 58]; ovigerous fræna, [ib.]; exuviation, [p. 61]; rate of growth, [ib.]; size, [ib.]; affinities of family, [p. 64]; range and habitats, [p. 65]; geological history, [p. 66.]
Metamorphoses.—I will here briefly describe the Metamorphoses, as far as known, common to all Cirripedia, but more especially in relation to the present family. I may premise, that since Vaughan Thompson’s capital discovery of the larvæ in the last stage of development in Balanus, much has been done on this subject: this same author subsequently published[4] in the ‘Philosophical Transactions,’ an account of the larvæ of Lepas and Conchoderma (Cineras) in the first stage; and seeing how totally distinct they were from the larva of the latter stage in Balanus, he erroneously attributed the difference to the difference in the two families, instead of to the stage of development. Burmeister[5] first showed, and the discovery is an important one, that in Lepas the larvæ pass through two totally different stages. This has subsequently been proved by implication to be the case in Balanus, by Goodsir,[6] who has given excellent drawings of the larva in the first stage; and quite lately, Mr. C. Spence Bate, of Swansea, has made other detailed observations and drawings of the larvæ of five species in this same early stage, and has most kindly permitted me to quote from his unpublished paper[7]. I am enabled to confirm and generalise these observations, in all the Cirripedes in the Order containing the Balanidæ and Lepadidæ.
[4] Philosophical Transactions, 1835, p. 355, Pl. vi.
[5] Beiträge zur Naturgeschichte der Rankenfüsser, 1834. Mr. J. E. Gray, however, briefly described, in 1833, (Proceedings, Zoological Society, October,) the larva in the first stage of Balanus; in this notice the anterior end of the larva is described as the posterior.
[6] Edinburgh New Philosophical Journal, July 1843, Pls. iii and iv.
[7] This will appear in the October number (1851) of the ‘Annals of Natural History.’
The ova, and consequently the larvæ of the Lepadidæ, in the First Stage, whilst within the sack of the parent, vary in length from .007 to .009 in Lepas, to .023 of an inch in Scalpellum: my chief examination of these larvæ has been confined to those of [Scalpellum vulgare]; but I saw them in all the other genera. The larva is somewhat depressed, but nearly globular; the carapace anteriorly is truncated, with lateral horns; the sternal surface is flat and broad, and formed of thinner membrane than the dorsal. The horns just alluded to are long in Lepas and short in Scalpellum; their ends are either rounded and excessively transparent, or, as in Ibla, furnished with an abrupt, minute, sharp point: within these horns, I distinctly saw a long filiformed organ, bearing excessively fine hairs in lines, so exactly like the long plumose spines on the prehensile antennæ of the larvæ in the last stage; that I have not the least doubt, that these horns are the cases in which antennæ are in process of formation. Posteriorly to them, on the sternal surface, near each other, there are two other minute, doubly curved, pointed horns, about .004 in length, directed posteriorly; and within these I again saw a most delicate articulated filiformed organ on a thicker pedicel: in an excellent drawing, by Mr. C. S. Bate, of the larva of a Chthamalus (Balanus punctatus of British authors), after having kept alive and moulted once, these organs are distinctly shown as articulated antennæ (without a case), directed forwards: hence, before the first moult in Scalpellum, we have two pair of antennæ in process of formation. Anteriorly to the bases of these smaller antennæ is seated the heart-shaped eye, (as I believe it to be,) .001 in diameter, with apparently a single lens, surrounded, except at the apex, by dark-reddish pigment-cells. In some cases, as in some species of Lepas, the larvæ, when first excluded from the egg, have not an eye, or a very imperfect one.
There are three pairs of limbs, seated close together in a longitudinal line, but some way apart in a transverse direction: the first pair always consists of a single spinose ramus, it is not articulated in Scalpellum, but is multi-articulate in some genera; it is directed forwards. The other two pair have each two rami, supported on a common haunch or pedicel: in both pair, the longer ramus is multi-articulate, and the shorter ramus is without articulations, or with only traces of them: the longer spines borne on these limbs (at least, in Scalpellum and Chthamalus,) are finely plumose. The abdomen terminates, a little beyond the posterior end of the carapace, in a slightly upturned horny point; a short distance anteriorly to this point, a strong, spinose, forked projection depends from the abdominal surface.
Messrs. V. Thompson, Goodsir, and Bate, have kept alive for several days the larvæ of Lepas, Conchoderma, Balanus, Verruca, and Chthamalus, and have described the changes which supervene between the first and third exuviations. The most conspicuous new character is the great elongation of the posterior point of the carapace into an almost filiform, spinose point in Lepas, Conchoderma, Chthamalus, and Balanus, but not according to Goodsir, in one of the species of the latter genus. The posterior point, also, of the abdomen becomes developed in Balanus (Goodsir) into two very long, spear-like processes, serrated on their outer sides; in Lepas and Conchoderma, according to Thompson, into a single, tapering spinose projection; and in Chthamalus, as figured by Mr. Bate, the posterior bifid point, as well as the depending ventral fork, increase much in size. Another important change, which has been particularly attended to by Mr. Bate, is the appearance of spinose projections and spines (some of which are thick, curved, and strongly plumose, or, almost pectinated along their inner sides) on the pedicels and lower segments of the shorter rami of the two posterior pairs of limbs.