[156] Any one who has not specially attended to the metamorphoses of ordinary cirripedes, who looks at the imaginary figure of the young [Proteolepas], will feel much surprise at the relative positions of the parts; for the mouth and the first and even second segments of the body stand posteriorly (i. e. above in the figure) to the succeeding segments of the body, in relation to the carapace of the pupa; but this is only in accordance with the remarkable change in position (as explained in the [introduction], p. [123], pl. [30], fig. [2]), amounting almost to inversion, which the whole thorax of every young cirripede undergoes within the pupa, whilst the anterior cephalic portions and general covering are developed conformably with the pupal carapace, whence it arises that the dorsal surface of that part of the thorax immediately succeeding the mouth becomes attached to the ventral internal surface of the carapace. I believe that the peculiar flattened dorsal outline of the first two segments of the body of [Proteolepas] is due to these parts having been formed in contact (as represented in pl. [25], fig. [6]) with the straight ventral surface of the carapace of the pupa. To place the young [Proteolepas], and at the same time the carapace of the pupa, with all the parts in proper homological sequence, it would be necessary to seize the posterior end of the abdomen (a), and pull till the dorsal surfaces of the first and second segments of the body, separated from the ventral internal surface of the carapace, and stood posteriorly (i. e. above in figure) to the mouth, which latter would thus also have to rotate a quarter of a circle, so that the orifice would come to be directed outwards. Then every part would stand, in accordance with the archetype crustacean structure, in due order; but the three confluent anterior cephalic segments, forming the front part and carapace of the pupa, would, as in the case of all cirripedes, be of disproportionately large size in relation to the rest of the body.
SYNOPSIS
ET
INDEX SYSTEMATICUS.
Ordinum, Familiarum, et Generum Cirripediorum et recentium et fossilium.
CLASSIS CRUSTACEA.
Sub-classis CIRRIPEDIA.
Crustacea ex anteriore capitis parte defixa, cæmento in hunc usum ex ovariorum portione ad id specialiter modificatâ emisso. Archetypus è segmentis 17 compositus, quorum 3 priora magna, in carapacem sæpissimè conformata, quæ non omnino exuitur et varios motus efficit: antennæ nullæ: oculi rudimentarii: os prominens, formatum è labro, palpis, mandibulis, et duobus maxillarum paribus, quæ omnia partim confluunt: thorax ad superficiem internam sternalem carapacis affixus, plerumque cum membrorum captantium biramorum, multiarticulorum paribus 6: abdomen plerumque rudimentarium: branchiæ, si quæ adsunt, ad inferiora carapacis latera affixæ: plerumque bisexualia; in unisexualibus, mares fœminis parasitice inserti: penis unicus, plerumque probosciformis, ad posteriorem abdominis extremitatem situs: oviductus nulli: metamorphoses multiplices.
ORDO I. [THORACICA]. (Darwin, ‘Balanidæ,’ p. [30].)
Cirripedia quibus pro carapace est aut capitulum pedunculatum, aut testa operculata cum basi. Corpus è 6 thoracicis segmentis, ferè cum 6 cirrorum paribus, constat. Abdomen rudimentarium, sed sæpe cum appendiculis caudalibus. Oris labrum motus proprios non efficit. Larva primò monocula cum 3 crurum paribus, postremò binocula cum 6 crurum thoracicorum paribus.
Familia 1. BALANIDÆ. (Darwin, ‘Balanidæ,’ p. [33].)
Cirripedia sine pedunculo: scuta et terga musculis depressoribus instructa: reliquæ testæ valvæ inter se immobiliter conjunctæ.