A Monograph on the Sub-class Cirripedia (Volume 1 of 2)

A Monograph on the Sub-class Cirripedia (Volume 1 of 2) - The Lepadidae; Or, Pedunculated Cirripedes

I should have been enabled to have made this Volume more complete, had I deferred its publication until I had finished my examination of all the other known Cirripedes; but my work would thus have been rendered inconveniently large. Until this examination is completed, it will be more prudent not to discuss, in detail, the position of the Lepadid amongst the Cirripedia, or of these latter in the great class of Crustacea, to which they now, by almost universal consent, have been assigned. I may, however, remark that I believe the Cirripedia do not approach, by a single character, any animal beyond the confines of the Crustacea: where such an approach has been imagined, it has been founded on erroneous observations; for instance, the closed tube within the stomach, described by M. Martin St. Ange (to whose excellent paper I am greatly indebted), as indicating an affinity to the Annelides, is, I am convinced, nothing but a strong epithelial lining, which I have often seen ejected with the excrement. Again, a most distinguished author has stated that the Cirripedia differ from the Crustacea:1st. In having a calcareous shell and true mantle; but there is no essential difference, as[Pg 2] shown by Burmeister, in the shells in these two classes; and Cirripedes certainly have no more claim to a mantle than have the bivalve entomostraca. 2d. In the sexes joined in one individual; but this, as we shall see, is not constant, nor of very much weight, even if constant. 3d. In the body not being ringed; but if the outer integument of the thorax of any Cirripede be well cleaned, it will be seen, (as was long ago shown by Martin St. Ange), to be most distinctly articulated. 4th. In having salivary glands; but these glands are, in truth, the ovaria. 5th. In the liver being formed on the molluscous type; I do not think this is the case, but I do not quite understand the point in question. 6th. In not having a head or organs of sense; this is singularly erroneous: Professor Leidy has shown the existence of eyes in the mature Cirripede; the antenn, though preserved, certainly become functionless soon after the last metamorphosis; but there exist other organs of sense, which I believe serve for smelling and hearing: and lastly, so far from there being no head, the whole of the Cirripede externally visible, consists exclusively of the three anterior segments of the head. The sub-class, Cirripedia, can be divided into three Orders; the first of which, mainly characterised by having six pair of thoracic cirri, includes all common Cirripedes: these latter may be divided into three families,the Lepadid, or pedunculated Cirripedes, the subject of the present memoir; the Verrucid containing the single genus Verruca or Clisia; and, lastly, the Balanid, which consist of two very distinct sub-families, the Balanin and Chthamalin. Of the other two Orders above alluded to, one will, I believe, contain the remarkable burrowing genus Alcippe, lately described by Mr. Hancock, and a second burrowing genus, or rather family, obtained by me on the coast of South America. The third Order is highly singular, and differs as much from all other Cirripedes as does a Lerna from other crustaceans; it has a suctorial mouth, but is destitute of an anus; it has[Pg 3] not any limbs, and is as plainly articulated as the larva of a fly; it is entirely naked, without valves, carapace, or capitulum, and is attached to the Cirripede, in the sack of which it is parasitic, by two distinct threads, terminating in the usual larval, prehensile antenn. I intend to call this Cirripede, Proteolepas. I mention it here for the sake of calling attention to any parasite at all answering to this description. NOMENCLATURE OF THE VALVES. ......Buy Now (To Read More)

Product details

Ebook Number: 31558
Author: Darwin, Charles
Release Date: Mar 8, 2010
Format: eBook
Language: English