A Monograph on the Sub-class Cirripedia Part 1

A Monograph on the Sub-cla.s.s Cirripedia.

by Charles Darwin.

PREFACE.

My duty, in acknowledging the great obligations under which I lie to many naturalists, affords me most sincere pleasure. I had originally intended to have described only a single abnormal Cirripede, from the sh.o.r.es of South America, and was led, for the sake of comparison, to examine the internal parts of as many genera as I could procure. Under these circ.u.mstances, Mr. J. E. Gray, in the most disinterested manner, suggested to me making a Monograph on the entire cla.s.s, although he himself had already collected materials for this same object.

Furthermore, Mr. Gray most kindly gave me his strong support, when I applied to the Trustees of the British Museum for the use of the public collection; and I here most respectfully beg to offer my grateful acknowledgments to the Trustees, for their most liberal and unfettered permission of examining, and when necessary, disarticulating the specimens in the magnificent collection of Cirripedes, commenced by Dr.

Leach, and steadily added to, during many years, by Mr. Gray.

Considering the difficulty in determining the species in this cla.s.s, had it not been for this most liberal permission by the Trustees, the public collection would have been of no use to me, or to any other naturalist, in systematically cla.s.sifying the Cirripedes.

Previously to Mr. Gray suggesting to me the present Monograph, Mr.

Stutchbury, of Bristol, had offered to intrust to me his truly beautiful collection, the fruit of many years' labour. At that time I refused this most generous offer, intending to confine myself to anatomical observations; but I have since accepted it, and still have the entire splendid collection for my free use. Mr. Stutchbury, with unwearied kindness, further supplied me with fresh specimens for dissection, and with much valuable information. At about the same period, Mr. c.u.ming strongly urged me to take up the subject, and his advice had more weight with me than that of almost any other person. He placed his whole magnificent collection at my disposal, and urged me to treat it as if it were my own: whenever I told him that I thought it necessary, he permitted me to open unique specimens of great value, and dissect the included animal. I shall always feel deeply honoured by the confidence reposed in me by Mr. c.u.ming and Mr. Stutchbury.

I lie under obligations to so many naturalists, that I am, in truth, at a loss how to express my grat.i.tude. Mr. Peach, over and over again, sent me fresh specimens of several species, and more especially of _Scalpellum vulgare_, which were of invaluable a.s.sistance to me in making out the singular s.e.xual relations in that species. Mr. Peach, furthermore, made for me observations on several living individuals. Mr.

W. Thompson, the distinguished Natural Historian of Ireland, has sent me the finest collection of British species, and their varieties, which I have seen, together with many very valuable MS. observations, and the results of experiments. Prof. Owen procured for me the loan of some very interesting specimens in the College of Surgeons, and has always given me his invaluable advice and opinion, when consulted by me. Professor E.

Forbes has been, as usual, most kind in obtaining for me specimens and information of all kinds. To the Rev. R. T. Lowe I am indebted for his particularly interesting collection of Cirripedes from the Island of Madeira--a collection offering a singular proof what treasures skill and industry can discover in the most confined locality. The well-known conchologist, Mr. J. G. Jeffreys, has sent for my examination a very fine collection of British specimens, together with a copious MS. list of synonyms, with the authorities quoted. To the kindness of Messrs. M^c Andrew, Lovell Reeve, G. Busk, G. B. Sowerby, Sen., D. Sharpe, Bowerbank, Hanc.o.c.k, Adam White, Dr. Baird, Sir John Richardson, and several other gentlemen, I am greatly indebted for specimens and information: to Mr. Hanc.o.c.k I am further indebted for several long and interesting letters on the burrowing of Cirripedes.

Nor are my obligations confined to British naturalists. Dr. Aug. Gould, of Boston, has most kindly transmitted to me some very interesting specimens; as has Prof. Aga.s.siz other specimens collected by himself in the Southern States. To Mr. J. D. Dana, I am much indebted for several long letters, containing original and valuable information on points connected with the anatomy of the Cirripedia. To Mr. Conrad I am likewise indebted for information and a.s.sistance. Both the celebrated Professors, Milne Edwards and Muller, have lent me, from the great public collections under their charge, specimens which I should not otherwise have seen. To Professor W. Dunker, of Ca.s.sel, I am indebted for the examination of his whole collection. I have, in a former publication, expressed my thanks to Professor Steenstrup, but I must be permitted here to repeat them, for a truly valuable present of a specimen of the _Anelasma squalicola_ of this work. I will conclude my thanks to all the above British and foreign naturalists, by stating my firm conviction, that if a person wants to ascertain how much true kindness exists amongst the disciples of Natural History, he should undertake, as I have done, a Monograph on some tribe of animals, and let his wish for a.s.sistance be generally known.

Had it not been for the Ray Society, I know not how the present volume could have been published; and therefore I beg to return my most sincere thanks to the Council of this distinguished Inst.i.tution. To Mr. G. B.

Sowerby, Junr., I am under obligations for the great care he has taken in making preparatory drawings, and in subsequently engraving them. I believe naturalists will find that the ten plates here given are faithful delineations of nature.

In Monographs, it is the usual and excellent custom to give a history of the subject, but this has been so fully done by Burmeister, in his 'Beitrage zur Naturgeschichte der Rankenfusser,' and by M. G. Martin St.

Ange, in his 'Memoire sur l'Organisation des Cirripedes,' that it would be superfluous here to repeat the same list of authors. I will only add, that since the date, 1834, of the above works, the only important papers with which I am acquainted, are, 1st. Dr. Coldstream 'On the Structure of the Sh.e.l.l in Sessile Cirripedes,' in the 'Encyclopaedia of Anatomy and Physiology;' 2d. Dr. Loven 'On the Alepas squalicola,' ('Ofversigt of Kongl. Vetens.,' &c. Stockholm, 1844, p. 192,) giving a short but excellent account of this abnormal Cirripede; 3d. Professor Leidy's very interesting discovery, ('Proceedings of the Academy of Natural Sciences,' Philadelphia, vol. iv, No. I, Jan. 1848,) of eyes in a mature Bala.n.u.s; 4th. Mr. A. Hanc.o.c.k's Memoir, ('Annals of Natural History, 2d series, Nov. 1849,) on his Alcippe lampas, the type of a new order of Cirripedes; 5th. Mr. Goodsir's Paper, ('Edinburgh New Philosoph.

Journal,' July 1843,) on the Larvae in the First Stage of Development in Bala.n.u.s; 6th. Mr. C. Spence Bate's valuable Paper on the same subject, lately published, (Oct. 1851,) in the 'Annals of Natural History;' and lastly, M. Reinhardt has described, in the 'Copenhagen Journal of Natural History, Jan. 1851,' the _Lithotrya Nicobarica_, and has discussed its powers of burrowing into rocks.

I have given the specific or diagnostic characters, deduced from the external parts alone, in both Latin and English. As I found, during the progress of this work, that a similarly abbreviated character of the softer internal parts, was very useful in discriminating the species, I have inserted it after the ordinary specific character.

In those cases in which a genus includes only a single species, I have followed the practice of some botanists, and given only the generic character, believing it to be impossible, before a second species is discovered, to know which characters will prove of specific, in contradistinction to generic, value.

In accordance with the Rules of the British a.s.sociation, I have faithfully endeavoured to give to each species the first name attached to it, subsequently to the introduction of the binomial system, in 1758, in the tenth edition[1] of the 'Systema Naturae.' In accordance with the Rules, I have rejected all names before this date, and all MS. names. In one single instance, for reasons fully a.s.signed in the proper place, I have broken through the great law of priority. I have given much fewer synonyms than is usual in conchological works; this partly arises from my conviction that giving references to works, in which there is not any original matter, or in which the Plates are not of a high order of excellence, is absolutely injurious to the progress of natural history, and partly, from the impossibility of feeling certain to which species the short descriptions given in most works are applicable;--thus, to take the commonest species, the _Lepas anatifera_, I have not found a single description (with the exception of the anatomical description by M. Martin St. Ange) by which this species can be certainly discriminated from the almost equally common _Lepas Hillii_. I have, however, been fortunate in having been permitted to examine a considerable number of authentically named specimens, (to which I have attached the sign (!) used by botanists,) so that several of my synonyms are certainly correct.

[1] In the Rules published by the British a.s.sociation, the 12th edition, (1766,) is specified, but I am informed by Mr.

Strickland that this is an error, and that the binomial method was followed in the 10th edition.

The Lepadidae, or pedunculated Cirripedes, have been neglected under a systematic point of view, to a degree which I cannot quite understand: no doubt they are subject to considerable variation, and as long as the internal surfaces of the valves and all the organs of the animal's body, are pa.s.sed over as unimportant, there will occasionally be some difficulty in the identification of the several forms, and still more in settling the limits of the variability of the species. But I suspect the pedunculated Cirripedes have, in fact, been neglected owing to their close affinity, and the consequent necessity of their being included in the same Work with the Sessile Cirripedes; for these latter will ever present, I am fully convinced, insuperable difficulties in their identification by external characters alone.

I will here only further remark, that in the Introduction I have given my reasons for a.s.signing distinct names to the several Valves, and to some parts of the included animal's body; and that in the Introductory Remarks, under the general description of the Lepadidae, I have given an abstract of my Anatomical Observations.

INTRODUCTION.

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 Lepadidae amongst the Cirripedia, or of these latter in the great cla.s.s of Crustacea, to which they now, by almost universal consent, have been a.s.signed. 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 sh.e.l.l and true mantle;" but there is no essential difference, as shown by Burmeister, in the sh.e.l.ls in these two cla.s.ses; and Cirripedes certainly have no more claim to a mantle than have the bivalve entomostraca. 2d. "In the s.e.xes 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 antennae, 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-cla.s.s, 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 Lepadidae, or pedunculated Cirripedes, the subject of the present memoir; the Verrucidae containing the single genus Verruca or Clisia; and, lastly, the Balanidae, which consist of two very distinct sub-families, the Balaninae and Chthamalinae. Of the other two Orders above alluded to, one will, I believe, contain the remarkable burrowing genus Alcippe, lately described by Mr. Hanc.o.c.k, 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 Lernaea from other crustaceans; it has a suctorial mouth, but is dest.i.tute of an a.n.u.s; it has 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 antennae. 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.

[Ill.u.s.tration: Figure I.

CAPITULUM.]

[Ill.u.s.tration: Figure II.

SCUTUM of LEPAS.]

[Ill.u.s.tration: Figure III.

TERGUM of LEPAS.]

Although the present volume is strictly systematic, I will, under the general description of the Lepadidae, give a very brief abstract of some of the most interesting points in their internal anatomy, and in the metamorphoses of the whole cla.s.s, which I hope hereafter to treat, with the necessary ill.u.s.trations, in detail. I enter on the subject of the metamorphoses the more readily, as by this means alone can the h.o.m.ologies of the different parts be clearly understood.

_On the Names given to the different parts of Cirripedes._

I have unwillingly found it indispensable to give names to several valves, and to some few of the softer parts of Cirripedes. The accompanying figure of an imaginary Scalpellum includes every valve; the two most important valves of Lepas are also given, in which the direction of the lines of growth and general shape differ from those of Scalpellum as much as they do in any genus. The names which I have imposed will, I hope, be thus acquired without much difficulty.

Whoever will refer to the published descriptions of recent and fossil Cirripedia, will find the utmost confusion in the existing nomenclature: thus, the valve named in the woodcut the _Scutum_, has been designated by various well-known naturalists as the "ventral," the "anterior," the "inferior," the "ante-lateral," and the "latero-inferior" valve; the first two of these t.i.tles have, moreover, been applied to the rostrum or rostral valve of sessile Cirripedes. The _Tergum_ has been called the "dorsal," the "posterior," the "superior," the "central," the "terminal," the "postero-lateral," and the "latero-superior" valve. The _Carina_ has received the first two of these identical epithets, viz.

the "dorsal" and the "posterior;" and likewise has been called the "keel-valve." The confusion, however, becomes far worse, when any individual valve is described, for the very same margin which is anterior or inferior in the eyes of one author, is the posterior or superior in those of another; it has often happened to me that I have been quite unable even to conjecture to which margin or part of a valve an author was referring. Moreover, the length of these double t.i.tles is inconvenient. Hence, as I have to describe all the recent and fossil species, I trust I may be thought justified in giving short names to each of the more important valves, these being common to the pedunculated and sessile Cirripedes.

The part supported by the peduncle, and which is generally, though not always, protected by valves, I have designated the _Capitulum_.

The t.i.tle of _Peduncle_, which is either naked or squamiferous, requires no explanation; the scales on it, and the lower valves of the capitulum, are arranged in whorls, which, in the Latin specific descriptions, I have called by the botanical term of verticillus.

I have applied the term _Scutum_ to the most important and persistent of the valves, and which can generally be recognised by the hollow giving attachment to the adductor scutorum muscle, from the resemblance which the two valves taken together bear to a s.h.i.+eld, and from their office of protecting the front side of the body. From the protection afforded by the two _Terga_ to the dorso-lateral surface of the animal, these valves have been thus called. The term _Carina_[2] is a mere translation of the name already used by some authors, of Keel-Valve.

[2] In the Carina of Fossil Species of Scalpellum, I have found it necessary to distinguish different parts, viz., A, the tectum, of which half is seen; B, the parietes; and C, the intra-parietes.

The _Rostrum_ has been so called from its relative position to the carina or keel. There is often a _Sub-carina_ and a _Sub-rostrum_.

The remaining valves, when present, have been called _Latera_; there is always one large upper one inserted between the lower halves of the scuta and terga, and this I have named the Upper Latus or Latera; the other latera in Pollicipes are numerous, and require no special names; in Scalpellum, where there are at most only three pair beneath the Upper Latera, it is convenient to speak of them (_vide_ Woodcut, I,) as the _Carinal_, _Infra-median_, and _Rostral Latera_.

As each valve often requires (especially amongst the fossil species) a distinct description, I have found it indispensable to give names to each margin. These have mostly been taken from the name of the adjoining valve, (see fig. I.) In Lepas, Pollicipes, &c., the margin of the scutum adjoining the tergum and upper latus, is not divided (fig. II) into two distinct lines, as it is in Scalpellum, and is therefore called the Tergo-lateral margin. In Scalpellum (fig. I) these two margins are separately named Tergal and Lateral. The angle formed by the meeting of the basal and lateral or tergo-lateral margins, I call the Baso-lateral angle; that formed by the basal and occludent margins, I call, from its closeness to the Rostrum, the Rostral angle. In Pollicipes the carinal margin of the tergum can be divided into an upper and lower carinal margin; of this there is only a trace (fig. I) in Scalpellum.

That margin in the scuta and terga which opens and _shuts_ for the exsertion and retraction of the cirri, I have called the Occludent margin. In the terga of Lepas (fig. III) and some other genera, the occludent margin is highly protuberant and arched, or even formed of two distinct sides.

Occasionally, I have referred to what I have called the _primordial valves_: these are not calcified; they are formed at the first exuviation, when the larval integuments are shed: in mature Cirripedes they are always seated, when not worn away, on the umbones of the valves.

The membrane connecting the valves, and forming the peduncle, and sometimes in a harder condition replacing the valves, I have often found it convenient to designate by its proper chemical name of _Chitine_, instead of by h.o.r.n.y, or other such equivalents. When this membrane at any articulation sends in rigid projections or crests, for the attachment of muscles or any other purpose, I call them, after Audouin, _apodemes_. For the underlying true skin, I use the term _corium_.

The animal's body is included within the capitulum, within what I call the _sack_ (see Pl. IV, figs. 2 and 8' _a_, and Pl. IX, fig. 4). The body consists of the _thorax_ supporting the cirri, and of an especial enlargement, or downward prolongation of the thorax, which includes the stomach, and which I have called the _prosoma_. (Pl. IX, fig. 4 _n_).