* * * * *
On the Moulting of the common Lobster (_Homarus vulgaris_) and Shore
Crab (_Carcinus mænas_). By S. JAMES A. SALTER, M.B., F.L.S., F.G.S.
[Read April 7th, 1859.]
I am induced to bring this subject before the Linnean Society, on
account of the singularly perfect specimen of the thrown-off slough of
a Lobster which I have now an opportunity of exhibiting, and because
the process by which it was shed was witnessed and carefully watched by
two competent observers--by my friend Mr. Robert Cooke, of Scarborough,
a Fellow of this Society, and by the intelligent wife of the Curator
of the Scarborough Museum, in an aquarium in which institution the
occurrence took place.
The methods by which certain of the Decapod Crustaceans cast their old
shells in the process of renewal and growth have already been made the
subject of observation and record.
Réaumur, as early as 1712, and again in 1718, saw and described the
sloughing of the common freshwater Crayfish (_Astacus fluviatilis_).
It was witnessed in the common edible Crab (_Cancer Pagurus_) by Mr.
Couch, in 1833.
Subsequently the moulting-process was observed by Mr. Gosse, in the
Spinous Spider-crab (_Maia Squinado_).
Beyond these three recorded examples, I believe that the actual
operation of moulting in Decapods has never been seen, though the
sloughs of our common Crustacea, and the animals themselves but recently
emerged from their old shells, are familiar to all marine zoologists.
There is no recorded account of the moulting of the Lobster, that I have
been able to discover.
The Lobster from which the slough was obtained, and whose operations
are the subject of this communication, was an inhabitant of a large
marine aquarium in the Museum at Scarborough. The period was July 1857.
The aquarium contained the ordinary assemblage of sea-shore animals,
and a considerable collection of vegetation, which consisted of _Ulva_,
_Fucus_, and other common sea-weeds.
For two days previous to its throwing off the shell, the Lobster was
observed in a very peculiar attitude, and to be very busily engaged.
Its abdomen was permanently and stiffly erected and straight; while the
animal, in this rigid attitude, was hard at work detaching and carrying
all the soft sea-weed it could collect to one end of the aquarium, where
it thus accumulated a large mass of vegetation, which was afterwards
destined to become a screen and protection for its soft body. At the
same time, and by the same means, a clearing was made at the other
end of the tank, in which it had space for the evolutions which were
subsequently necessary for the extrication of its body.
The Lobster remained in the peculiar rigid attitude I have described,
during the entire two days previous to the moult. On the third day, a
crack was observed along the membrane which unites the dorsal surface
of the first abdominal ring with the carapace; and when these parts
became separated by about half an inch, the bright-blue membrane of the
new shell being plainly visible beneath, the operation of extricating
the abdomen commenced. By a strong vibratory action of the whole
abdomen, principally in a lateral direction, one segment was, at first,
protruded through the split; and this was followed by an interval of
complete repose, during which the animal remained quite motionless.
Then, by another vibratory action, the second segment was extricated;
then followed an interval of repose, when the third was withdrawn; and
so on till, at last, the entire abdomen, after having been bent double
upon itself, was turned completely out backwards, and then, elongated
and compressed, remained above and parallel to the empty shell that it
had occupied, and which was still attached to the under surface of the
cephalothorax. Hitherto the only orifice of escape consisted in the
transverse splitting of the first abdominal segment from the carapace,
on the dorsal surface. None of the abdominal segments separated from
each other.
Thus far the extrication had commenced at the front of the abdomen,
and had progressed from before backwards. It was now observed that
the carapace had split from behind forwards, the fissure commencing
posteriorly at the transverse split between _the_ carapace and the
first abdominal segment, and reaching forwards to the apex of the
rostrum, which, however, it did not absolutely divide. The two halves
of the carapace then separating posteriorly, the interval between
them, together with the original transverse slit, constituted a trifid
opening, through which the rest of the animal escaped.
The escape of the cephalo-thoracic portion was effected from behind
forwards. First the posterior ambulatory legs were loosened and
withdrawn; then followed the next pair; and this process was continued
from behind forwards, pair by pair--the withdrawal of each pair of legs
being followed by an interval of repose. The limbs were withdrawn very
readily from the old shell, slipping out of it as a leg would from a
loose boot. No apparent effort accompanied these operations so far.
The extrication of the claws, however, was attended with much and
violent exertion. This consisted of two powerful and sudden tugs, the
soft abdomen of the Lobster pressing by its under surface upon the
upper surface of the empty shell. By this means the soft chelæ were
drawn through the narrow joints of the old shell, exhibiting strong,
unmistakeable marks of the violence and pressure to which they had been
subjected. The escape of the chelæ from their unyielding incasement
was not aided by any splitting of the old shell, the large soft hands
being drawn by compression through the narrow joints, as a wire is drawn
through the contracting holes of a draw-plate.
The efforts for the withdrawal of the chelæ were the last, and succeeded
in completely freeing the Lobster from its old case. Not only the
claws, but the parts of the mouth, the antennæ, and the eyes, were
all unsheathed; and with the last tug the regenerate Lobster plunged
backwards, and entirely escaped, above and behind the now empty
shell--its former tenement.
The operation, from first to last, occupied about twenty minutes, and
was performed entirely in view, in that part of the aquarium which the
Lobster had cleared of sea-weed.
Immediately after emerging from the old shell, the Lobster, was much
deformed: there was a general elongation of the whole animal; but this
was most remarkably the case with the claws, which were quite drawn out
of shape. During the few subsequent hours, both the body and the claws
became shorter and much enlarged. This increase of size did not result
from any unfolding of membrane of the shell previously plicated, as no
folds were observable immediately after the emergence of the animal,
but from a simple distension, apparently from the imbibition, either
by swallowing or by endosmosis, of considerable quantities of water.
The membrane of the new shell was perfectly soft, and of a bright blue
colour. At first the Lobster was shy and quite inactive, retiring to
and remaining concealed among the accumulated sea-weed; but in a few
hours it emerged from its retreat, and moved freely about the aquarium.
The membrane of the new shell remained soft for some days, but on the
seventh it appeared to have become perfectly calcified.
These are the details of the exuviation of the Lobster whose cast-off
shell is before the Society. By a happy accident, the same observers had
an opportunity of witnessing the sloughing of another Lobster, in the
month of November following. The process was identically the same in
every particular; but it was observed that the subsequent calcification
of the shell did not take place till after the lapse of about fourteen
days,--a circumstance probably dependent on a lower temperature and a
less active nutrition. These are, I believe, the only two instances in
which the exuviation of the Lobster has been actually witnessed; but
there exist specimens of sloughs which are entirely in keeping with this
description. In the fish-house of the Zoological Society of London there
are two specimens which were cast in the tanks there; and in each there
is the same transverse splitting of the carapace from the abdomen, and
the longitudinal splitting of the carapace itself, without any other
opening for the escape of the animal.
One or two general observations are suggested by the foregoing
description. In the only examples of the exuviation of macrourous
Decapod Crustaceans, there exists a singular diversity in the
process itself. In _Astacus_, as described by Réaumur, the process
commences with the escape of the cephalothorax; in _Homarus_, as I
have now described it, it begins by the emergence of the abdomen. In
_Astacus_ the carapace is detached and thrown off bodily and unbroken,
being severed from its attachments with the lateral portions of the
cephalothorax, as is the case in the Brachyura; whereas in _Homarus_ the
lateral attachments of the carapace remain, whilst the plate itself is
split up the centre. In _Astacus_, as is also the case in the Brachyura,
the thrown-off slough is uniformly left resting on its dorsal surface;
in _Homarus_ the reverse is uniformly the case. But the most striking
dissimilarity is to be found in the circumstances _stated_ to attend the
liberation of the chelæ. Prof. Bell, in the Introduction to his 'History
of the British Stalk-eyed Crustacea,' remarks--"It is impossible to
imagine that the crust of the legs, and especially of the great claws
of the larger species, could be cast off, unless it were susceptible of
being longitudinally split" (p. 35), and he then proceeds to give the
account detailed by Réaumur of the longitudinal splitting of the shell
in the neighbourhood of the joints of the claws in _Astacus_, so as to
allow of the extrication of the hands. Nevertheless, however impossible
it may appear for the chelæ to escape without this splitting, no such
circumstance occurs in the exuviation of _Homarus vulgaris_; and when
we consider that the hands of _Astacus_ are small in proportion to
the wrist-joints, and that in _Homarus_ they are larger in proportion
to those joints than in any other of the Macroura, this dissimilarity
in the mode in which the claws escape is the more remarkable, and, I
confess, to my own mind it suggests the suspicion that the distinguished
and usually most accurate French naturalist to whom I have referred may
possibly in this instance have been led to consider as a fact that which
was to him a supposed necessity[9].
Since the foregoing account of the moulting of the Lobster was written,
I have dredged a specimen of the common shore-crab (_Carcinus mænas_),
in the act of casting its shell. This little crustacean had taken
refuge, no doubt for the safe and secret performance of sloughing in
a forest of _Zostera_, on one of the mud banks in Poole Harbour, and
while scraping these weeds with a keer-drag it fortunately fell into my
net. It shows how the Brachyura leave their old shells by the horizontal
splitting away of the carapace from the other portions of the shell--the
carapace itself remaining entire; and it also shows (and this was my
principal object in exhibiting the specimen) the enormous amount of
increase of size upon emerging from the shell, and the rapidity with
which that increase takes place. The animal, as now seen, is in exactly
the same state as when taken out of the water, and its bulk is probably
some four times larger than the area of the shell in which it had been
encased only a few minutes before. I retained the Crab in connexion with
its old shell, and prevented its further escape by wrapping it in paper,
so that it could not move its limbs. I thought such a specimen would
be telling and illustrative, and that the old shell, being in contact
with the new, would afford facilities for contrast. In this condition
the Crab died, and, being out of water some time, it became dry, and
the soft new shell collapsed and bulged in; but, upon placing the dead
Crab in sea-water, the soft shell very speedily imbibed sufficient
fluid to distend it to its previous dimensions. This of course was
simply the effect of endosmosis. Mr. Couch, in describing the moulting
of the common Edible Crab (_Cancer Pagurus_), speaks of its _drinking_
large quantities of water, and _thus_ becoming distended; but I rather
think that the distension takes place by endosmosis, even during
life. There are two circumstances which militate against Mr. Couch's
opinion:--first, the rapidity with which the distension occurred in the
Crab I have just exhibited, while still in the act of moulting; and
secondly, that after death the same distension occurred when the Crab
was immersed in sea-water; in which case it could only be by endosmosis.
Indeed to me it seems very probable that this very endosmosis, when the
water once comes in contact with the new, uncalcified shell, may, by
distending it, be the main agent in the breaking open and dissevering of
the elements of the old shell.
[9] The suspicion above expressed has been fully confirmed by
observations made by Mr. J. J. Bennett, the Secretary of the
Linnean Society. Mr. Bennett informs me that, in an aquarium in
his possession, an _Astacus fluviatilis_ has twice cast its shell,
and the process of moulting was on each occasion accomplished
without any splitting of the shell at the joints of the claws.
* * * * *
On the Shell-bearing Mollusca, particularly with regard to Structure
and Form. By ROBERT GARNER, Esq., F.L.S.
[Abstract of a Paper read before the Society.]
The author commences the paper, of which the following is the substance,
with some general observations on the morphology of animals. He thinks
that the idea of an ascending and successive scale or chain of creation
is, in the main, correct, when the great classes, and not species or
genera, are made the links,--the disturbing or modifying influences
being due to modes of life, food, habitat, &c., and causing a different
(say the quinary) distribution. He is an advocate, too, for the doctrine
of one fundamental plan of organization, and thinks that, in the
zoophyte, there is a real union of both the animal and vegetable
_nisus_.
The great divisions of this chain, the _radiate_, _articulate_,
_molluscous_, and _vertebrate_, constitute an ascending series; the
links of the chain, so to speak, being in each case, for such an
extent, of a particular pattern; but, nevertheless, one of the highest
mollusks may surpass in organization one of the lowest fishes, or an
articulate creature a mollusk. The author considers such great divisions
of animals, as well as minor ones--the gasteropodous mollusks, for
instance--as realities, and not mere abstractions; and that they are
independent of the circumstances of food, habitat, locomotion, &c.,
just referred to. So great, however, are these disturbing influences,
that they often produce an extraordinary external resemblance or
pseudo-analogy between animals of a very different nature, as between
a _Chiton_ and an _Oniscus_, and they are connected intimately with,
though not the cause of, what we call specific or generic distinctions.
Aërial life, in contradistinction to aquatic, raises much the character
of the locomotive organs; yet this is subordinate to type: hence the
creeping Mollusk appears to have commonly a higher organization than the
flying Insect.
The cartilages of _Sepia_ have a true resemblance to those of a Skate,
and the Cirrhipede truly connects the Mollusk with the Crustacean.
The author regards _Dentalium_ as a gasteropod, differing in this
respect from Lacaze-Duthiers, whose beautiful paper, however, renders
it supererogatory to say anything more on this animal, except that
the author believes that the presence of the spiniferous tongue, of a
proboscis, and the nature of the food, are favourable to his view: he
also takes the feathery tufts to be the branchiæ.
The anatomy of _Aspergillum_ is similar to that of _Pholas_; its mantle,
however, is all but closed in front, and ends in an obliquely-set
muscular disk, applied to the internal surface of the rose of the
so-called _arrosoir_, the openings of this part of the shell giving exit
to certain processes and fimbriæ of the fleshy disk,--a narrow slit
being also left in both the muscular and shelly disks for the exsertion
of the small, compressed and curved foot. The animal is enveloped
within the shell by a rather horny, general membrane.
The author touches upon the anatomy of some other genera of
Lamellibranchiata. _Solemya_ has its firm, horny, dark cuticle doubled
inwards from the valves over the tubular mantle; behind, it has an anal
opening, and a second fringed branchial slit lower down: the branchiæ
and tentacles are single on each side, the former being remarkably
feather-like. The foot is similar to that of the Solens, but crenate
round its anterior disk. _Cyrenoidea_ has the mantle closed below, but
with two openings behind, the upper one with a semicircular internal
fringe, incomplete above; a callous rim and fringe surround the mantle,
which has also a third opening for the long, compressed, bent, and
blunt foot. This last has a remarkable crystalline body, directed from
the stomach to the pedal pore, apparently, as in _Cardium_, subserving
by its elasticity to the extension of the foot, and consequently to
locomotion; at any rate, it is not a sexual distinction. The external
branchiæ are short, and the upper or internal branchial cavity does
not communicate with the lower one. The renal organ opens near the
branchial nerve, and the ovary at the base of the abdominal mass.
_Trigonia_ is remarkable for its beautifully fringed, open mantle,
its pectinated pits for the secretion of the teeth, and the large
scythe-shaped foot, trenchant before and peaked behind, and having a
fringed disk. _Vulsella_ is allied to the Oyster, but more so to the
Pectens, having a small cylindrical grooved foot and appended visceral
mass, but no byssus; the rectum perforates the heart, and has a tentacle
above its opening. _Perna_ has a similar foot, and a very bulky byssus,
with a large muscle attached to their base; the lips resemble those
of the Oyster. The anatomy of _Crania_ is little different from that
of _Orbicula_, as described by Owen,--the beautiful arms folded in
several coils, with a simple mouth at their base, the stomach and short
intestinal canal surrounded by the liver and hearts, and terminating
by a lateral bend; the ovaries ramifying in the mantle; the adductor
muscles being four in number, with some bands to the mantle; and on
the latter, glandular markings corresponding with the microscopic
sculpture of the shell. With respect to _Anomia_, the author has again
been anticipated by Lacaze-Duthiers, though he has already given, in
another paper, most of its anatomy and morphology: he would simply call
attention to its very long and curious crystalline stilette, unconnected
with the minute foot.
With respect to that _quæstio vexata_, the sexes of the
Lamellibranchiata, he observes that any number of individuals of
_Cyclas_ may be examined, and young fry will be found in the branchial
laminæ in all; that all Oysters have ova, and also all individuals of
_Pecten maximus_, the subpedal mass being visibly composed of an ovary
and a testis. He is obliged to believe that one species of British
_Anodon_ is universally oviferous. But the common Edible Cockle appears
to have the individuals of different sexes, and the same may be said
with regard to _Mytilus edulis_ and _Patella_.
The spermatozoa in the Cockle are oblong and a little curved, and
torulated, as it were, whilst they are pear-shaped in _Mytilus_; they
are also extremely minute, and their appendages must be very fine, for
with a power magnifying 500 diameters they are scarcely to be seen.
In the shell of a _Patella_, _Emarginula_, or _Haliotis_, we have the
two conjoined valves of a lamellibranchiate mollusk; and through such
forms as _Calyptræa_, _Hipponyx_, _Navicella_, and _Nerita_, we arrive
at the ordinary form of the gasteropod with its operculum.
Then follows a disquisition on the progressive tendency to a spiral
geometry in these animals, due to a varying plan of conformation,
and not to the force of the heart, there being generally an atrophy
of the left side of the body. In _Nautilus_ and _Argonauta_, the
shell and mantle are reversed in position to what they are in the
Gasteropods, whilst _Sepia_ and _Hyalæa_ agree rather with the latter.
The symmetrical shell of the lower Gasteropods undergoes a lateral
torsion in the higher, spiral forms, to become again symmetrical in
the Cephalopoda. The branchiæ in _Patella_ retain a position analogous
to that of the same organs in the Lamellibranchiata; in some Chitons
they have a tendency to retract towards the anus, as in _Doris_; in
_Fissurella_ they waste at the sides and become developed above the
neck, as in the spiral Gasteropods; but in them, the right branchia,
and right side of the mantle are principally developed. From this
torsion arises the form and spire of the shell. In _Aplysia_, where
the branchial fissure is far back and to the right side, the right
respiratory nerve preserves a superior position, and passes backwards to
form its ganglion at the front of the branchial opening; the left, on
the contrary, passes under the oesophagus to form a second ganglion,
not mentioned by Cuvier, behind the first. In the more spiral Gasteropod
the torsion is greater; the right nerve, for instance, mounts upwards
over the digestive canal to form its ganglion quite in the left flank,
whilst the left goes below the digestive canal to attain the right
flank. In _Sepia_ the branchiæ are again symmetrical and abdominal.
The shell of the young _Sepia_ is composed of distant plates, only
connected by minute transversely striated laminæ or flattened tubes,
producing by their insertion a beautiful appearance of sinuous lines,
very like those of a Baculite or Ammonite; and the spongy part of the
shell, so constituted, is probably filled with air from the cavity of
the body situated immediately in front, the intervening membrane having
a peculiar structure. This cavity of the body exists in much lower
mollusks; air being apparently secreted in it, to lighten the animal.
The author thinks that, in considering the anatomy and form of the
body of the Gasteropoda, about ten species may be taken as types of
corresponding families.
1. PATELLA _and its congeners_.--He claims to have been one of the
first to show the termination of the oviducts and renal organs between
the processes of the branchiæ in the Chitons. As they are commonly
phytivorous, the intestine is often very long and disposed in large
coils, in double apposition; the buccal apparatus is very remarkable.
_Chitonellus_ differs but slightly from _Chiton_, the central elements
of its tongue, however, being little developed, though having the same
tessellated basement membrane. The tongue of _Emarginula_ differs much
from that of _Patella_, having an immense number of serrated side-hooks
and a dilated middle portion.
2. CALYPTRÆA, _&c._--The mollusks of this division have often
supranuchal branchiæ, as have some of the last; the sexes also are
frequently separate, rendering copulation necessary; and they are
sometimes partially spiral, with a tendency to form an operculum.
However, the little _Ancylus fluviatilis_ appears to be what is commonly
called hermaphrodite, with a branchial lamina on the left side, together
with the heart and openings of the genital organs; the stomach has a
cæcum, and the penis a long filiform appendage; the female parts opening
near the rectum and behind the male organs. It must respire by water
rather than by air, for, in a rapid stream, the stones at the bottom
are covered with _Ancyli_ (upon which also its round oothecæ, each
containing four or five ova, are deposited), and it appears impossible
for them to get to the surface to breathe. On the contrary, the
lake-_Ancylus_, though the margin of its mantle is ciliated, may perhaps
come to the surface, ascending the stalks of the Water Persicaria, on
which it is mostly found, and on which its oothecæ are deposited. When
the dark cuticle of this last minute creature is removed, its organs
may be seen to be reversely disposed to those of the larger species, the
heart being placed to the right, before the apex of the shell, and the
rectum also on the same side.
3. DORIS, _&c._--The little _Doris aspera_ swims, back downwards,
on the surface of a glass of sea-water, copulates, and deposits its
semicircular oothecæ. The brain of the common Lemon Doris is of a fine
orange colour, enveloped in a glandular matter, and is constituted by
a complicated assemblage of ganglia: there are acoustic sacs and dark
ocular spots upon it. There are six ganglia on the buccal mass, and
about six or eight minute ones on the stomach. The anal sac appears
to be a purple- or ink-bag; and the so-called matrix is composed of a
peculiar substance, swelling enormously in water, of which it renders
a large quantity viscid, and being also coagulable by alcohol and
bichloride of mercury, but not by heat. Spermatozoa were found in the
genital vesicle, as well as in the epididymis and its cæcum. The spines
of the lingual plate are uniform, and in number about 10,000.
4. APLYSIA, _&c._--_Aplysia_ has been before alluded to. Cuvier, in
his generally beautiful drawings, has scarcely done justice to (5)
_Ianthina_, nor to its beautiful float and ootheca; it is peculiar
for its fins, and the disk at the back of the foot. With respect to
_Magilus_, it should be removed from the (6) Tubulibranchiata, its
animal being a _Purpura_ in structure, with a bent horny operculum, and
a very long linear appendage on the right side of the head, leading to
the supposition that the animals are of different sexes, though there
seem to be difficulties in the way of sexual congress. In the specimen
examined, the spire of the shell was not solidified; the animal had a
short proboscis, with rather bent subulate feelers, and eyes on the
outside; it had also a rich purple secretion near the rectum on the
right side.
7. TROCHUS, _&c._--Some of the species of _Trochus_ surpass even
_Emarginula_ in the beauty of their lingual apparatus. The renal
organ opens into the bottom of the branchial cavity, contrary to its
disposition in _Helix_ and _Lymnæus_, where its exit is near the
respiratory orifice. In _Planorbis_, that part of the respiratory cavity
receiving the excretions seems separated by an imperfect valve from the
right portion. With respect to the secretion of this organ, it consists,
in both Gasteropoda and Lamellibranchiata, of numerous pellucid globular
bodies, containing opaque earthy nuclei or granules, and presenting
different appearances in _Anodon_ (for instance), _Cyclostoma_,
_Buccinum_, and _Helix_. When these bodies are incinerated, lime is
left, which in some cases appears to have been combined with oxalic
acid. The little _Nerita litoralis_ presents the structure of the
Turbonidæ very prettily and in small compass, particularly in the very
long spiral tongue. _Delphinula_ has the fringed mantle and sides and
very wonderfully armed tongue of the other Trochidæ. _Melania_ is of
similar organization to our well-known _Paludina_, the stomach compound,
the mantle and bilobed head fringed, and the latter marbled like that of
_Paludina_. _Ampullaria_ appears to be truly amphibious.
8. BUCCINUM, _&c._--_Natica_ presents much the same structure as the
common _Buccinum_, but has a muscular disk anterior to the mouth,--a
disposition, with some variations however, found in other mollusks. The
first and second stomachs are at a distance from each other, the tongue
is little developed, and the branchiæ (often single in the Turbonidæ)
two in number. _Purpura_ also differs but little from _Buccinum_.
_Ovula_ is a less attainable mollusk: the foot is long and rather
narrow, and subventral rather than subtrachelian, with a sinuosity on
the right of the neck, where also is a short hooked penis in the male,
receiving a vas deferens from near the rectum behind; there is a large
and small branchia, and the reflected portion of the mantle is covered
with tubercles and tentacles,--no doubt a fine garnish in the living
animal; the mouth has a muzzle, and there are small eyes on the external
sides of the curved, awl-shaped tentacles; the elements of the tongue
are beautifully toothed and serrated.
9. LYMNÆUS, _&c._--Of the air-breathing aquatic and (10) terrestrial
gasteropods the most interesting particulars are their generative
organs, which the author proposes to re-examine. The brain of _Helix
aspersa_ is composed internally of pyriform or oval ganglionic vesicles,
each giving origin to one or more nervous fibres. The acoustic sacs
are similar to those of _Doris_. The nerves from the upper part of the
ring are enveloped in a darkish neurilema, and comprehend no doubt
olfactory, optic, and tactile twigs; there being the buccal ganglia for
taste, and the acoustic sacs for hearing; the twigs, however, forming
the buccal or pharyngeal ganglia have a broad double root on each side,
near the origin of the above three nerves. The lower part of the brain
is very analogous to that of _Sepia_, giving off nerves to the foot,
and external and internal respiratory ones to the mantle, respiratory
opening, branchiæ, &c. _Lymnæus_ has the cephalic ring formed by about
twelve ganglia, exclusive of two large and two minute ones on the buccal
mass. The upper portion of the ring has ganglionic swellings, but in
other respects the nerves are as in _Helix_. Its lower portion consists
of two pedal nerves, and has the acoustic spot and a minute ganglion
upon it; behind, this lower portion consists of five ganglia connected
with both the anterior and upper swellings by a cord, but separated from
the former by the aorta, as usual, and giving nerves to the flanks,
pulmonary orifices and sac, heart, stomach, and viscera. The lower
ganglia are bright yellow.
With respect to the Pteropoda, the branchiæ in _Hyalæa_ exist as a
delicate membrane under the swollen part of the shell, in structure
much like the same part in the Ascidians, the inlet being through the
anterior opening of the mantle. There are eyes at the fold of the
mantle behind, and two small tentacles above the mouth; the heart and
rectum being on the left side, and the generative opening at the base
of the right ala. _Cleodora_ is a very beautiful creature, with the
same disposition and structure of viscera; brain-spots but no eyes
were visible; the mantle had beautiful muscular bands; the branchiæ as
above; the buccal apparatus is imperfect in both. _Cleodora_ has similar
membranous expansions with _Hyalæa_, and also a sort of triangular lip.
_Argonauta_ has a lachrymal pore before and beneath the eye. The
beautiful and obvious respiratory mechanism in the Cephalopoda needs
not to be described. There is a large sac behind the viscera of the
Argonaut, which opens on each side; it is perhaps of some hydrostatic
use. There are at least three pairs of salivary glands, of which four
open on the floor of the mouth, and two or three at the commencement
of the gullet. Several small shells of Pteropoda and fragments of
Cephalopods were found in the stomach, on which was observed the large
nervous ganglion found in all these, as well as in lower mollusks.
The branchial nerves have each two ganglia, of which the last at the
root of the branchiæ is rounder than the other; the branchial hearts
have processes as in _Sepia_. In _Sepia_ two openings lead from the
respiratory sac into the cavity containing the venæ cavæ and their
secreting appendages often imbued with glittering crystalline particles,
and from the above cavities a wider opening on each side leads into
a second sac further back, situated in front of the shell. There are
auditory sacs in the Argonaut. The oviducts have separate openings, but
originate together. Both _Sepia_ and _Argonauta_ are infested with a
subcutaneous filiform entozoon, hooked anteriorly and rolled up spirally
in the former. _Loligo media_ and _Sepiola_ have but one oviduct, and
the two large, glandular, laminated organs, opening at their summits,
are wanting in _Argonauta_ and _Octopus_. In _Sepiola_ one would almost
think that copulation takes place, for the author has taken what he
supposes to be the capsules of Needham, with dilated oval ends, tubular
and bent pedicles or processes, enclosed elastic filaments, and adhering
zoosperms, from the oviducts of the female: he has made the same
observation also in _Sepia_. The latter has very similar male organs
to _Octopus_, as described by Cuvier. In the embryo _Sepia_, the yelk
enters below the mouth and opens into the upper stomach, but the beak
of the animal also appears to be inserted into it behind. The vitellus
in reality therefore enters by the foot, as it does in _Bulimus_, and
probably in all Bivalves.
* * * * *