THE
RAY SOCIETY.
INSTITUTED MDCCCXLIV.
[Illustration]
LONDON.
MDCCCLI.
A MONOGRAPH
ON THE SUB-CLASS
CIRRIPEDIA,
WITH
FIGURES OF ALL THE SPECIES.
BY
CHARLES DARWIN, F.R.S., F.G.S.
THE LEPADIDÆ;
OR,
PEDUNCULATED CIRRIPEDES.
LONDON:
PRINTED FOR THE RAY SOCIETY.
MDCCCLI.
C. AND J. ADLARD, PRINTERS, BARTHOLOMEW
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
shores 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 circumstances, Mr. J. E. Gray, in the most disinterested manner,
suggested to me making a Monograph on the entire class, 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 class, 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 classifying 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. Cuming
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. Cuming and Mr. Stutchbury.
I lie under obligations to so many naturalists, that I am, in truth, at
a loss how to express my gratitude. Mr. Peach, over and over again, sent
me fresh specimens of several species, and more especially of
_Scalpellum vulgare_, which were of invaluable assistance to me in
making out the singular sexual 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, Hancock, Adam White, Dr. Baird, Sir John Richardson, and
several other gentlemen, I am greatly indebted for specimens and
information: to Mr. Hancock 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. Agassiz 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 assistance. Both the celebrated
Professors, Milne Edwards and Müller, have lent me, from the great
public collections under their charge, specimens which I should not
otherwise have seen. To Professor W. Dunker, of Cassel, 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 assistance 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 Institution. 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
‘Beiträge zur Naturgeschichte der Rankenfüsser,’ and by M. G. Martin St.
Ange, in his ‘Mémoire sur l’Organisation des Cirripèdes,’ 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 Shell in Sessile Cirripedes,’ in the ‘Encyclopædia of Anatomy and
Physiology;’ 2d. Dr. Lovén ‘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
Balanus; 4th. Mr. A. Hancock’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 Larvæ in the First Stage of Development in
Balanus; 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 Association, 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 Naturæ.’ In accordance with the
Rules, I have rejected all names before this date, and all MS. names. In
one single instance, for reasons fully assigned 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 Association, 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 Lepadidæ, 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 passed 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 assigning 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 Lepadidæ, I have given an
abstract of my Anatomical Observations.
CORRIGENDA AND ADDENDA.
Page
12, twenty lines from bottom, _for_ “hinder pair of true thoracic
limbs,” _read_ “pair of true thoracic limbs.”
42, 43. I should have added, that the number of the segments in the
cirri increases with the age of the specimen; but that the
relative numbers in the different cirri keep, as far as I have
seen, nearly constant; hence the numbers are often given in
the descriptions.
99 et passim, _for_ Pæcilasma, _read_ Poecilasma.
156. In a foot-note, I have alluded to a new genus of sessile
Cirripedes, under the name of Siphonicella, I now find that
this species has been called, by Professor Steenstrup,
_Xenobalanus globicipitis_.
MONOGRAPH
ON
THE CIRRIPEDIA.
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 Lepadidæ
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 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 antennæ, 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 Lepadidæ, or pedunculated Cirripedes, the subject of the
present memoir; the Verrucidæ containing the single genus Verruca or
Clisia; and, lastly, the Balanidæ, which consist of two very distinct
sub-families, the Balaninæ and Chthamalinæ. 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 Lernæa from other crustaceans; it has a suctorial
mouth, but is destitute of an anus; 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 antennæ. 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.
[Illustration: Figure I.
CAPITULUM.]
[Illustration: Figure II.
SCUTUM of LEPAS.]
[Illustration: Figure III.
TERGUM of LEPAS.]
Although the present volume is strictly systematic, I will, under the
general description of the Lepadidæ, give a very brief abstract of some
of the most interesting points in their internal anatomy, and in the
metamorphoses of the whole class, which I hope hereafter to treat, with
the necessary illustrations, in detail. I enter on the subject of the
metamorphoses the more readily, as by this means alone can the
homologies 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 titles 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 titles 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 title 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 shield, 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 horny, 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_).
The cirri are composed of two arms or _rami_, supported on a common
segment or support, which I call the _pedicel_. The _caudal appendages_
are two little projections, either uni-or multi-articulate (Pl. IV, fig.
8´ _a_), on each side of the anus, and just above the long
proboscis-like penis. On the thorax and prosoma, or on the pedicels of
the cirri, there are in several genera, long, thin, tapering filaments,
which have generally been supposed to serve as branchiæ; these I call
simply _filaments_, or _filamentary appendages_ (Pl. IX, fig. 4 _g-l_).
The mouth (fig. 4 _b_) is prominent, and consists of _palpi_ soldered to
the _labrum_; _mandibles_, _maxillæ_, and _outer maxillæ_, these latter
serve as an under lip; to these several organs I sometimes apply the
title used by Entomologists, of “trophi.” Beneath the outer maxillæ,
there are either two simple orifices or tubular projections; these, I
believe, serve as organs of smell, and have hence called them the
_olfactory orifices_. Within the sack, there are often two sheets of ova
(Pl. IV, fig. 2 _b_), these I call (after Steenstrup, and other
authors) the _ovigerous Lamellæ_; they are united to two little folds of
skin (Pl. IV, fig. 2 _f_), which I call the _ovigerous Fræna_.
From the peculiar curved position which the animal’s body occupies
within the capitulum, I have found it far more convenient (not to
mention the confusion of nomenclature already existing) to apply the
term Rostral instead of ventral, and Carinal instead of dorsal, to
almost all the external and internal parts of the animal. Cirripedes
have generally been figured with their surfaces of attachment downwards,
hence I speak of the lower or Basal margins and angles, and of those
pointing in an opposite direction as the Upper; strictly speaking, as we
shall presently see, the exact centre of the usually broad and flat
surface of attachment is the anterior end of the animal, and the upper
tips of the Terga, the posterior end of that part of the animal which is
externally visible; but in some cases, for instance in Coronula, where
the base is _deeply concave_, and where the width of the shell far
exceeds the depth, it seemed almost ridiculous to call this, the
anterior extremity; as likewise does it in Balanus to call the united
tips of the Terga, lying deeply within the shell, the most posterior
point of the animal, as seen externally.
I have followed the example of Botanists, and added the interjection [!]
to synonyms, when I have seen an authentic specimen bearing the name in
question.
Every locality, under each species, is given from specimens ticketed in
a manner and under circumstances appearing to me worthy of full
confidence,--the specific determination being in each case made by
myself.
CLASS--CRUSTACEA. SUB-CLASS--CIRRIPEDIA.
FAMILY--LEPADIDÆ.
_Cirripedia pedunculo flexili, musculis instructo: scutis[3] musculo
adductore solummodô instructis: valvis cæteris, siquæ adsunt, in annulum
immobilem haud conjunctis._
Cirripedia having a peduncle, flexible, and provided with muscles.
Scuta[3] furnished only with an adductor muscle: other valves, when
present, not united into an immovable ring.
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.
[3] The meaning of this and all other terms is given in the
Introduction, at pp. 3-7.
_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.
The mouth in its earliest condition alone remains to be described; in
_S. vulgare_, it is seated on a very slight prominence, in a most
remarkable situation, namely, in a central point between the bases of
the three pairs of legs. I traced by dissection the oesophagus for some
little way, until lost in the cellular and oily matter filling the whole
animal, and it was directed anteriorly, which is the direction that
might have been expected, from the course followed by the oesophagus in
the larva in the last stage, and in mature Cirripedes. Mr. A. Hancock
has called my attention to a probosciformed projection on the under side
of the larva of _Lepas fascicularis_, when just escaped from the egg.
Mr. Bate has described this same proboscis in Balanus and Chthamalus,
and states the important fact, that it is capable of being moved by the
animal; and, lastly, I have seen it in an Australian Chthamalus, and in
Ibla, of remarkable size. This proboscis, which is always directed
posteriorly, (like the mouth in the mature animal,) certainly answers to
the mouth as made out by dissection in Scalpellum; and I believe I saw,
as has Mr. Bate, a terminal orifice: it certainly does not possess any
trophi. In Ibla (in which the larva is large enough for dissection), the
base of the proboscis arises posteriorly to the first pair of legs, and
the orifice at the other end reaches beyond or posteriorly to the point,
where the mouth in Scalpellum opens, namely between the middle pair of
legs. The mouth being either so largely probosciformed or seated only on
a slight eminence, in two genera so closely allied as Ibla and
Scalpellum, and (judging from Mr. Thompson’s figures, and from what I
have seen myself,) in the species of the same genus Lepas, is a singular
difference: in the cases in which, at first, the proboscis is absent, it
would probably soon be developed. I cannot but suppose that the inwardly
directed spines on the bases of the two posterior legs, which are so
rapidly developed, serve some important end, namely, as organs of
prehension for the larvæ, like the mandibles and maxillæ of mature
Cirripedes, for seizing their prey, and conveying it to their moveable
mouths, conveniently seated for this purpose.
The first pair of legs answers, as I believe from reasons hereafter to
be assigned, to the outer pair of maxillipods in the higher crustacea;
and the other four legs to the first two pair of thoracic limbs in these
same crustacea; this being the case, the highly remarkable position of
the mouth in the larva, either between the bases of the two posterior
pair of legs, or at least posteriorly to the first pair, together with
the probable functions of the spiny points springing from the basal
segments of the two hinder pair of true thoracic limbs, forcibly bring
to mind the anomalous structure of the mouth being situated in the
middle of the under side of the thorax, in Limulus,--that most ancient
of crustaceans, and therefore one likely to exhibit a structure now
embryonic in other orders. I will only further remark, that I suspect
that the truncation of the anterior end of the carapace, has been
effected by the segments having been driven inwards, and consequently,
that the larger antennæ within the lateral horns, though standing more
in front than the little approximate pair, are normally the posterior
of the two pair. According to Milne Edwards, the posterior pair are
normally seated outside the anterior pair, and this is the case with
those within the lateral horns.
_Larva in the Second Stage._--Notwithstanding the considerable changes,
already briefly given, which the larva undergoes during the first two or
three exuviations after leaving the egg, all these forms may be
conveniently classed under the first stage. The larva in the Second
stage is known only from a single specimen described, figured, and found
by Burmeister,[8] adhering to sea-weed in the midst of other larvæ of
Lepas in the last stage. In its general shape and compressed form, it
seems to come nearer to the last than to the first stage. It has only
three pair of legs, situated much more posteriorly on the body than in
the first stage, and all directed posteriorly; they are much shorter
than heretofore, and resemble rather closely those of the last stage,
with the important exception that the first pair has only one ramus. It
is this circumstance which leaves no doubt on my mind, that we here have
the three pair of limbs, of the first stage, metamorphosed. The body is
prolonged some way behind these limbs, and ends in a blunt, rounded
point, in which, probably, are developed the three posterior pair of
legs and the abdomen of the larva in the last stage. The mouth is now
seated some way anteriorly to the limbs, is large and probosciformed,
and is, I presume, still destitute of trophi. There are now two closely
approximate eyes, but as yet both are _simple_. The smaller pair of
antennæ has disappeared. The whole animal was attached to the sea-weed
by a (I presume, pair of,) “fleischigen Fortsatz,” which Burmeister
considers as the prehensile antennæ, to be presently described, in an
early state of development. I have little doubt that this is correct,
for in an abnormal Cirripede of another order, in which the larva
appears in the _first_ stage with prehensile antennæ, the eggs have two
great projecting horns including these organs, and attached by their
tips, through some unknown means, to the sack of the parent, apparently
in the same manner as Burmeister’s larva was attached to the sea-weed. I
will only further remark on the larva of this Second stage, that its
chief development since the first stage, has been towards its anterior
end. The next great development, to be immediately described, is towards
the posterior end of the animal.
[8] Beiträge zur Naturgeschichte der Rankenfüsser, s. 16, Tab. i,
figs. 3, 4.
_Larva, Last Stage._--My chief examination has been directed, at this
stage of development, to the larvæ of _Lepas australis_, which are of
unusual size, namely, from .065 to even almost .1 of an inch in length;
I examined, however, the larvæ of several other species of Lepas, of
Ibla and of Balanus, with less care, but sufficiently to show that in
all essential points of organisation they were identical; this, indeed,
might have been inferred from the similarity of the larval prehensile
antennæ, preserved in the bases of all mature Cirripedes, and which I
have carefully inspected in almost every genus. The larvæ in this final
stage, in most of the genera, have increased many times in size since
their exclusion from the egg; for instance, in _Lepas australis_, from
.007 to .065, or even to .1 of an inch. They are now much compressed,
nearly of the shape of a cypris or mussel-shell, with the anterior end
the thickest, the sternal surface nearly or quite straight, and the
dorsal arched. Almost the whole of what is externally visible consists
of the carapace; for the thorax and limbs are hidden and enclosed by its
backward prolongation; and even at the anterior end of the animal, the
narrow sternal surface can be drawn up, so as to be likewise enclosed.
As in several Stomapod crustaceans, the part of the head bearing the
antennæ and organs of sense, in front of the mouth, equals, or even
exceeds in length, and more than exceeds in bulk, the posterior part of
the body, consisting of the enclosed thorax and abdomen. I will now
briefly describe, in the following order, the carapace, the organs of
sense, mouth, thorax and limbs, abdomen, and internal viscera.
The form of the _Carapace_ has been sufficiently described; it consists
of thick chitine membrane, marked with lines, and sometimes with stars
and other patterns; it is obscurely divided into two halves by a line or
suture along part of the dorsal margin; these halves or two valves are
drawn together by an adductor muscle, in the same relative position as
in the mature Cirripede. The part overhanging and enclosing the thorax
is lined by an excessively delicate membrane, obviously homologous with
the lining of the sack in the mature animal, and is nothing but a
duplicature of the carapace, rendered very thin from being on the under
or protected side: a layer of true skin or corium, probably double,
separates these two folds.
_Acoustic Organs._--On the borders of the carapace, at the anterior end,
on the sternal surface, there are two minute orifices, in _L. australis_
.002 in diameter, sometimes having a distinct border round them; the
membrane of the carapace on the inside is prolonged upwards and inwards
in two short funnel-shaped tubes, lodged in closed sacks of the corium:
within these sacks on each side a delicate bag is suspended, and hangs
in the mouth of the above funnel; at the upper end a large nerve could
be distinctly seen to enter the bag: I cannot doubt that this is a
sense-organ; from its position and from the animal not feeding (as we
shall presently see), I conclude that it is an acoustic organ.
_Antennæ._--These are large and conspicuous; they are attached very
obliquely on the sternal surface, a little way from the anterior end of
the carapace, beyond which, when exserted, they extend;[9] they can (at
least in Ibla) be retracted within the carapace. They consist of three
segments: the first or basal one is much larger than the others, and
apparently always has a single spine on the outer distal margin. The
second segment consists either of a large, thin, circular, sucking disc,
or is hoof-like (Tab. V, figs. 5, 10, 11, 12); in all cases it is
furnished with one or more spines, (seven very long ones in Lepas,) on
the exterior-hinder margin. The third and ultimate segment is small; it
is articulated on the upper surface of the disc, and is directed
rectangularly outwards; it is sometimes notched, and even shows traces
of being bifid; it bears about seven spines at the end; some of these
spines are hooked, others simple, and in _Lepas_ and _Conchoderma_, two
or three are very long, highly flexible, and plumose, a double row of
excessively fine hairs being articulated on them. I can hardly doubt
that these latter spines, (within which the purple corium could be seen
to enter a little way,) floating laterally outwards, serve as feelers.
The antennæ, at first, are well furnished with muscles. They serve, in
Lepas, according to Mr. King, and in Balanus, according to Mr. Bate, and
as I saw myself in another unnamed order, for the purpose of walking,
one limb being stretched out before the other; but their main function
is to attach the larva for its final metamorphosis into a Cirripede. The
disc can adhere even to so smooth a surface as a glass tumbler.[10] The
attachment is at first manifestly voluntary, but soon becomes
involuntary and permanent, being effected by special and most remarkable
means, which will be most conveniently described in a later part of this
Introduction. I will here only state that I traced with ease the two
cement-ducts running from two large glandular bodies, to within the
antennæ up to the discs.
[9] Mr. J. D. Dana, who has examined these organs in the larvæ of
Lepas, informs me in a letter, that in his opinion they
“correspond with the inferior antennæ, the superior being
wanting, as in most Daphnidæ.” He continues--“I know of no case
in which the inferior are obsolete when the superior are
developed; but the reverse is often true.” In position these
antennæ certainly correspond to the inferior and central pair of
the larva in the first stage, which belong, as it would appear,
to the first segment of the body; but judging from the drawing by
Burmeister of the larva in the second stage, I am, in some
respects, more inclined to consider that they correspond to the
larger pair seen within the lateral horns of the carapace in the
first stage.
[10] Rev. B. L. King. Annual Report of B. Institution of
Cornwall, 1848, p. 55.
_Eyes._--Close behind the basal articulations of the antennæ, the
sternal surface consists of two approximate, elongated, narrow, flat
pieces, or segments. These Burmeister considers as the basal segments
of the antennæ: as they are not cylindrical, I do not see the grounds
for this conclusion: their posterior ends are rounded, and the membrane
forming them is reflected inwards, in the form of two, forked, horny
apodemes, together resembling two letters, =UU=, close together; these
project up, inside the animal, for at least one third of its thickness
from the sternal to the dorsal surface. The two great, almost spherical
eyes in _L. australis_, each 1/150th of an inch in diameter, are
attached to the outer arms, thus, =°UU°=, in the position of the two
full stops. Hence the eyes are included within the carapace. Each eye
consists of eight or ten lenses, varying in diameter in the same
individual from 1/2000 to 3/2000th of an inch, enclosed in a common
membranous bag or cornea, and thus attached to the outer apodemes. The
lenses are surrounded half way up by a layer of dark pigment-cells. The
nerve does not enter the bluntly-pointed basal end of the common eye,
but on one side of the apodeme. The structure here described is exactly
that found, according to Milne Edwards, in certain crustacea. In
specimens _just attached_, in which no absorption has taken place, two
long muscles with transverse striæ may be found attached to the knobbed
tips of the two middle arms of the two =°UU°=, and running up to the
antero-dorsal surface of the carapace, where they are attached; other
muscles (without transverse striæ) are attached round the bases, on both
sides of both forks. The action of these muscles would inevitably move
the eyes, but I suspect that their function may be to draw up the
narrow, deeply folded, sternal surface, and thus cause the retraction of
the great prehensile antennæ within the carapace.
_Mouth._--This is seated in exactly the same position as in the mature
Cirripede, on a slight prominence, fronting the thoracic limbs, and so
far within the carapace, that it was obviously quite unfitted for the
seizure of prey; and it was equally obvious, that the limbs were
natatory, and incapable of carrying food to the mouth. This enigma was
at once explained by an examination of the mouth, which was found to be
in a rudimentary condition and absolutely closed, so that there would be
no use in prey being seized. Underneath this slightly prominent and
closed mouth, I found all the masticatory organs of a Cirripede, in an
immature condition. The state of the mouth will be at once understood,
if we suppose very fluid matter to be poured over the protuberant mouth
of a Cirripede, so as to run a little way down, in the shape of internal
crests, between the different parts, and in the shape of a short,
shrivelled, certainly closed tube, a little way (.008 of an inch in _L.
australis_) down the oesophagus. Hence, the larva in this, its last
stage, cannot eat; it may be called a _locomotive Pupa_;[11] its whole
organisation is apparently adapted for the one great end of finding a
proper site for its attachment and final metamorphosis.
[11] M. Dujardin has lately (‘Comptes Rendus,’ Feb. 5, 1850, as
cited in ‘Annals of Nat. History,’ vol. v, p. 318,) discovered
that the “Hypopi are Acari with eight feet, without either mouth
or intestine, and which, being deprived of all means of
alimentation, fix themselves at will, so as to undergo a final
metamorphosis, and they become Gamasi or Uropodi.” Here, then, we
have an almost exactly analogous case. M. Dujardin asks--“Ought,
therefore, the Hypopi to be called larvæ, when, under that
denomination, have hitherto been comprised animals capable of
nourishing themselves?”