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HUNTERIAN LECTURES.

LECTURES

COMPARATIVE ANATOMY,

DELIVERED AT THE

ROYAL COLLEGE OE SURGEONS,

In 1843;

PROFESSOE OWEN, F.R.S. &c.

HUNTERIAN PROFESSOR TO THE COLLEGE ;

FROM NOTES TAKEN BY (uJ * s-

WILLIAM WHITE COOPER, M.R.C.S^'

FELLOW OF THE ROYAL MEDICAL AND CHIRURGICAL SOCIETY, E

REVISED BY PROFESSOR OWEN.

ILLUSTRATED BY NUMEROUS WOODCUTS.

Sontiott :
LONGMAN, BROWN, GREEN, AND LONGMANS,

PATERNOSTER ROW.

1843.

f

ADVERTISEMENT,

Having been imbued with a love for Comparative Anatomy
by the Lectures delivered by Professor Owen at St. Bartholo-
mew's Hospital in 1835 (the first I had attended on the subject),
I have availed myself of the opportunities which have been
afforded by the courses of Lectures that have since been an-
nually delivered by the same distinguished Professor in the
Theatre of the Royal College of Surgeons, to keep pace with
the rapidly advancing sciences of Zootomy and Physiology.

Of these valuable Lectures I have been in the habit of taking
full notes, many of which, having been kindly revised by
Professor Owen, have received his approbation for their
fidelity.

Having reason to believe that such notes would be acceptable
to the members of the Profession and other scientific men, as
well as the lovers of Natural History generally, I have obtained
the sanction of Professor Owen to publish those of the Hunterian
Lectures for the present year. The notes will be revised by
the Professor, who has also kindly promised to furnish the sub-
jects of the most instructive diagrams used in illustration of the
Lectures, and which will be incorporated by means of wood-
cuts with the text.

I should not be doing justice to my own feelings did I not
avail myself of the present opportunity of expressing the deep

2 ADVERTISEMENT.

sense of gratitude I feel towards Professor Owen as well for
tills as for tlie many other favours I have received at his hands
during a period of nearly ten years : and I shall endeavour, to
the best of my abilities, to discharge my present undertaking in
a manner which may not be unworthy of the importance of the
subject.

WILLIAM WHITE COOPER.

2. Tenterden Street,
Hanover Square.

HUNTERIAN LECTURES

<0^Al}\ 1843.

^A-^'C.--5-^K^0DUCT0RY LECTURE.

' '^ CLASSIFICATION OF ANIMALS.

Mr. President and Gentlemen,
There are doubtless some now present who have not before attended
the Himterian lectures on Comparative Anatomy, which are appointed
to be annually delivered in this theatre. I may therefore commence
by stating the prescribed extent and subject of these lectures.

They are defined in the second clause of the trust-deed, which ex-
presses the conditions on which the Hunterian Collection, purchased
by Parliament, was transferred to the Royal College of Surgeons, as
follows : viz. " That one course of lectures, not less than twenty- four in
number, on Comparative Anatomy, illustrated by the Preparations,
shall be given each year by some member of the College."

When I was honoured by the Council in 1837 with this arduous and
responsible office, it seemed to me that the first obligation upon the
professor was, to combine with the information to be imparted on the
science of Comparative Anatomy an adequate demonstration of the
nature and extent of the Hunterian Physiological Collection, and thus
to offer a due tribute to the scientific labours and discoveries of its
Founder.

The system adopted by Hunter for the arrangement of his pre-
parations of Comparative Anatomy was therefore made that of the
lectures which were to be illustrated by them ; and this plan was closely
adhered to until the whole of the physiological department of the
Collection had been successively brought under your notice, and its
demonstration completed, in the course of lectures which I had the
honour to deliver last year.

It is, I believe, generally known that Hunter has arranged his beau-
tifully prepared specimens of animal and vegetable structures according
to the organs ; commencing with the simplest form, and proceeding

B 2

31295

4 INTRODUCTORY LECTURE.

through successive gradations to the highest or most complicated con-
dition of each organ.

These series of organs from different species are arranged according
to their relations to the great functions of organic and animal life ; and
the general scheme is closely analogous to that adopted by Baron
Cuvier in his Legons cCAnatomie Comparee, and in the best modern
works on Physiology. The only difference seems to be, that the series
of the organs subservient to the functions of animal life are interposed,
by Hunter, between those which relate to the organic life of the indi-
vidual and those which illustrate the great function of generation or
perpetuation of the species.

The lectures which I delivered in this theatre in the years 1837,
1838, and 1839, were on the comparative anatomy and physiology of
digestion, nutrition, circulation, respiration, excretion, and the tegu-
mentary system. In 1840, the comparative anatomy of the generative
organs, and the development of the ovum and foetus in the different
classes of animals, were treated of. The organs of the animal functions
next engaged our attention, and a review of the fossil' remains of
extinct animals was combined with the osteology of existing species.
The comparative anatomy and physiology of the nervous system, which
was the subject of last year's course, terminated the series commenced
in 1837 on the plan which 1 have just defined.

I have the pleasure to see the friendly countenances of some here
present who have patiently, and I hope not unprofitably, listened to
the whole of this series of lectures, and who may have discerned in
it, notwithstanding the long and frequent intervals, the characters of
a single and connected scheme of instruction in Comparative Anatomy
and Physiology. But with regard to those gentlemen, the students of
medicine and surgery in this metropolis, to whom I have the greatest
wish to impart profitable and useful instruction, I have seen, with
regret^ that portions only of the extensive subject, which the fulness
of its treatment compelled me to divide amongst different courses of
lectures, have been listened to by successive tenants of the gallery.*
The leisure left to the students of medicine, after the arduous task of
acquiring the essential elements of their profession, has rarely allowed
them to avail themselves of the privilege of admission to this theatre
for more than one or two seasons; and I fear that none have
been able to serve with us .throughout our six years' siege of the
city of physiological science founded by Hunter.

The advantage — the necessity, rather — of combining a general

* The gallery of the theatre is appropriated to the students; the body of the
theatre to the members and council of the college. W. W. C.

CLASSIFICATION OF ANIMALS. 5

knowledge of tlie organisation of the lower animals with that of man,
Avhich ought always to claim the first attention of the medical student,
is now universally recognised. A great part, often the best part, of
the proofs of the most important physiological doctrines are derived
from Comparative Anatomy. The increasing taste for the natural
sciences, and the rapidly diffusing knowledge of zoology and geology,
render it scarcely pardonable in a member of a liberal profession
to be wholly unversed in them; and almost discreditable to a
medical man to be unable to offer any sound opinion on a fossil coral,
shell, or bone which may be submitted to his inspection, or on the
other surprising phenomena of animal life, as the animal origin of
chalk and flint, which geology from time to time educes from the
dark recesses of the earth, and makes a common topic of con-
versation.

There is no just ground to. fear that the time required to gain the
requisite elementary knowledge of Comparative Anatomy will detract
from that which ought to have been exclusively occupied in the study
of human anatomy and surgery ; or that the subsequent pursuit of
natural science will interfere with the proper professional duties.

There is generally a period of leisure during the first years of
practice which may be most agreeably and profitably devoted to
scientific pursuits ; and the young provincial surgeon may be assured
by the example of Gideon Mantell, that the researches and dis-
coveries in palaeontology and geology, which have added so many
honourable titles to that name, are quite compatible with the most
extensive, active, and successful practice.

It has been a subject of much consideration with me, having
fulfilled, in one respect, the obligations to the memory of the founder
of the Collection, how to present the general principles and leading
facts of Comparative Anatomy with most profit and utility to my junior
auditors ; and I trust that the plan which I propose to adopt for the
present course and that of next year will enable me to give a complete
view of the science within that space, which shall not be less sub-
servient to the illustration of Physiology than were the preceding
lectures given on the system indicated by the arrangement of the
Hunterian Prej^arations.

It is very true that, by tracing the progressive additions to an organ
through the animal series from its simplest to its most complex struc-
ture, we learn what part is essential, what auxiliary to its office ; and
the successive series of preparations in Hunter's Physiological Col-
lection strikingly and beautifully illustrate this connection between
Comparative Anatomy and Physiology, But it is by the comparison
of the particular grades of complication of one organ with that of

B 3

6 INTRODUCTORY LECTURE,

another organ in the same body, by considering them in relation to
the general nature and powers of the entire animal^, together with
its relations to other animals, and to the sphere of its existence, that
we are chiefly enabled to elucidate the uses of the several super-
additions which are met with in following out the series of com-
plexities of a single organ.

Comparative Anatomy fulfils only a part of its services to Physiology,
if studied exclusively in relation to the varieties of a given organ in
different animals : the combinations of all the constituent organs in
one animal must likewise be studied ; and these combinations with
the principles governing them, or the correlations of organs, must
be traced and compared in all their varieties throughout the animal
kingdom.

It is in this point of view that I now propose to bring before you
the leading facts of Comparative Anatomy, to discuss and demonstrate
the organs as they are combined in the individual animal, and, com-
mencing with the lowest organised species in which the combination
is of the simplest kind, to trace it to its highest state of complexity
and perfection, through the typical species of the successively ascend-
ing primary groups and classes of the animal kingdom. In short, as
my previous courses of Hunterian lectures, agreeably with the
arrangement of the Hunterian Collection, have treated of Com-
parative Anatomy according to the organs, in the ascending order, so,
in the present course, Comparative Anatomy will be considered ac-
cording to the class of animals, and also in the ascending scale.

Many examples suggest themselves of the advantage of this mode
of studying the organisation of animals for the purpose of acquiring
just conceptions of the uses of the organs. In tracing, for example,
the progressive complication of the heart, we first find the simple
dorsal vessel; it is next concentrated into a ventricle, and to this
single cavity an auricle is afterwards appended : then the auricle
becomes divided ; afterwards there are two ventricles : there are
instances even in the animal kingdom where there are three ventricles
and ten ventricles. Now, the two-cavitied, dicoelous, or bipartite
heart is met with in the snail and in the fish ; but the physiology of
such conformation of the organ can only be explained by its connec-
tions with other organs, and by the general structure and habits of
the animal.

First, then, as to the connections of the bipartite heart. In the
snail it is so placed, in reference to the breathing organ, that it
receives the aerated blood from that organ and propels it to the
system: it is an organ for the circulation of arterial blood; in other
words, a systemic heart. The bipartite structure of the central organ

CLASSIFICATION OF ANIMALS. 7

of circulation, compared with lower or higher conditions of the same
organ, could never have taught that fact ; — the knowledge of it
necessitates and pre-supposes a knowledge of the relation of the
heart to the lungs.

In [the fish the bipartite heart is so connected with the breathing
organs, that it transmits exclusively to them the blood which the
auricle receives from the veins of the body : it is an organ for the cir-
culation of venous blood ; in other words, a " pulmonic heart." An-
other question then arises. Why is the dicoelous heart in one animal
systemic, in another animal pulmonic ? This can only be answered
by a further insight into the organisation and powers of such animals.
With respect to the instances adduced, both species are cold-blooded,
and, compared with the warm-blooded classes, both have a low amount
of respiration ; but the fish and snail differ widely in the degree in
which they exercise or enjoy the respiratory functions. The snail,
proverbially sluggish and inactive, has its muscular system reduced
almost to a single ventral disc, by the successive contractions of the
parts of which it glides slowly along. The chief mass of its body is
made up of the organs of the vegetative function. We see here a wide
convoluted alimentary canal, an enormous liver, a large ovarium and
as large a testis combined with many singular accessory generative
organs, in the same common visceral cavity : they make up the great
bulk of its body. The tissues of such viscera are endued with little
of that action which assists in the acceleration of the currents of blood,
through them ; and, therefore, the greater circulation is aided by the con-
tractions of a ventricle: whilst as the function of respiration bears ever
a direct ratio to the energy and frequency of muscular action, it suffices
that the venous blood should flow with an equable and unaccelerated
stream over the oxygenating surface, and the energies of the heart
are therefore confined to the service of the general circulation.

In the fish, the proportions of the muscular and visceral parts are
reversed : the greater part of the body is composed of the vibrating
and contractile fibre, by the action of which the fish is propelled through
the liquid medium ; while at the same time the systemic circulation
is proportionally aided and accelerated. But this amount and energy
of muscular action requires a proportional activity of the respiratory
function, and the forces of the heart are, therefore, concentrated upon
the gills.

Thus we perceive that a similar construction of an organ may, through
its different relations with other organs, subserve different functions :
whilst the conditions of such differences demand for their elucidation,
a knowledge of the general organisation and endowments of the entire
animal.

B 4

S INTRODUCTORY LECTURE.

Permit me to give anotlier instance of the necessity of studying
the whole organisation and relations of an animal in order to learn
the physiology of the modification of one of its organs.

In tracing the progressive complications of the stomach, we at length
meet with it under that very singular condition which we term a
gizzard ; in which the cavity is reduced to a mere fissure, by the accu-
mulation of muscular fibres in its walls, and by a thick and callous
lining of dense horny matter. The physiologists who viewed this
modification of a stomach, without reference to the rest of the or-
ganisation of the bird, and who contented themselves by experimenting
upon the compressive and triturating force of the gizzard, were led to
conclude that digestion was mainly a mechanical process. They were
here misled by Comparative Anatomy ; but it was by its abuse.

Graminivorous and granivorous birds — those species whose
food demands the most complete comminution — have that mecha-
nical process performed, it is true, exclusively by the gizzard ; but
near this triturating stomach we find another cavity as exclusively
secretory in its functions, and which we know, by experiment, to fur-
nish a powerful solvent in great quantities to act upon the comminuted
food. But why the comminuting machinery should be transferred
to the abdominal cavity in the bird requires for its explanation a
review of the general structure, habits and sphere of existence, of this
particular form of animal.

The most prominent quality in the bird is its power of flight — to
lighten the extremities and accumulate the weight at the centre of
gravity favour this power : it is especially requisite that the head,
which is supported on a long and flexible neck, should be as light as
possible. To this end the jaws, instead of supporting dense and heavy
teeth, are wholly edentulous, and are sheathed with light horn ; they
are simply prehensile, not masticatory^ organs ; and the muscular
masses, subserving mastication, are consequently uncalled for. The
compensation is admirably adjusted in harmony with the exigencies
of the bird : pebbles are swallowed to serve as teeth; are collected in
the gizzard, near the centre of gravity, of the whole body, at which
point the muscular mass required to operate upon them, and, by their
means, to crush the grain, is likewise concentrated. Thus the teeth, and
masticatory muscles are removed from the head, and concentrated in
the stomach, at the centre of gravity of the bird ; and the peculiarities
of its stomach are thus found, by a general survey of the organisation
and habits of the animal, to relate to the acquisition of certain me-
chanical advantages in the disposition of the weight of the body, so as
to favour the act of flight.

I might easily multiply such instances, but I should thus only

CLASSIFICATION OF ANIMALS. 9

anticipate the illustrations of which the present course of lectures
will mainly consist.

Not only the soundest and widest physiological generalisations, but
those inductions which, from sometimes being based on a mere
fragment of a bone, seem like a divination of the nature and affinities
of an extinct species, depend entirely upon a knowledge of the laws
of correlation of organic structures, and can only be made by the
comparative anatomist, who has studied not only the gradations of
structure, but the general combinations of organs which characterise
the species of each particular class.

With these explanations of the grounds which have lead me to
change the order in which I propose to bring before you the facts of
Comparative Anatomy, I proceed to the proper business of the
present course, which must commence by the definitions of the
primary groups of animals whose general plan of organisation it is
proposed to describe and compare.

Little useful progress can be made in Comparative Anatomy
without some knowledge of Zoology. Zoology is the key to the
nature and habits of the animals of which Zootomy unfolds the
structure. Some knowledge of natural history and of the principles
of classification, therefore, is essential to the comprehension of the con-
nection between structure and habits, on which the utility of Com-
parative Anatomy in the advancement of Physiology mainly depends.

The classification of animals is not now what it was in the time of
Linnaeus. I do not mean merely to say that animals are differently
arranged, but the object and principles of that arrangement are very
different.

Linnaeus in his Systema Naturce wished to give, as it were, a
Dictionary of the Animal Kingdom, by reference to which you might
as readily ascertain the place of the animal in his system as that of a
word in a lexicon, by merely knowing its first and second letters.
To this end, Linnaeus selected a few of the most obvious characters
for the establishment of his groups.

Taking, for example, a certain number of incisor teeth, and the
pectoral position of the mammae, as the characters of his first order of
animals, he thereby associated man with the monkeys and the bats.
But, independently of the psychical endowments which place the
human species far above the lower creation, it may readily be
conceived that great differences of organisation must exist in animals
which enjoy the erect position on two feet, in those which climb by
having four hands, and in those which fly by virtue of a metamor-
phosis of tlieir anterior members into wings.

External and arbitrary characters, selected merely for the con-

10 INTRODUCTORY LECTURE.

venieiice of their appreciation, thus tend to the association of very
differently organised species ; and, on the other hand, they are equally
liable to separate into very remote groups of an artificial system,
two animals which may have very similar anatomical structures.
Of this we have several examples in the Linnaean subdivisions of the
class of fishes, the orders of which are characterised by the easily
recognisable position of the fins. Linnaeus's attention was par-
ticularly directed to the very variable position of the ventral pair of
fins, which are the analogues of the hinder limbs in land animals.
In some fishes, as the pike and many other fresh-water species, the
ventral fins are at some distance behind the pectoral fins, or in their
usual place — these formed the order Abdomincdes : in others, as the
perch, the ventral fins are attached beneath the thorax — these
constituted the Thoracic order : in others, as the cod, you find the
ventral fins in advance of the pectorals, or under the throat — such
species formed the Pisces jugulates of Linnaeus : lastly, those
species in which the ventral fins are altogether wanting, as the eel,
formed the Apodal order.

Such a system has the advantage of enabling the collector to refer
with great facility any fish to its artificial order ; but you can scarcely
express any general proposition in comparative anatomy in reference
to such groups. There are two sword-fishes, for example, having the
same anatomical structure, and not easily distinguishable externally
save by the height of the dorsal and the difference in the position of
the ventral fins : but in the Systema Naturce of the Swedish Na-
turalist, the Xiphias is placed in one order, and the Istiophorus in
another ; the variable and little influential fins prevailing over all the
rest of the organisation in the artificial ichthyology of Linnaeus.

Amongst the lower animals, we find the slug, placed in one class,
viz. the Vermes mollusca^ and the snail in a different class, viz. Vermes
testacea, in the Systema NaturcE ; whilstin their wholeanatomy these two
mollusca most closely resemble each other, the rudimental state of the
shell being the main difference in the Limax or slug. Similar instances
of the violation of natural affinities might be multiplied, and are, indeed,
inevitable in an artificial system.

I confess that if the classifications of zoology of the present day
continued to be of the same character as that to which I have just
referred, which however, let it be remembered, was the best that could
be made in the time of Linnaeus, and a necessary transitional step to
improved view's on this subject, I should not have been justified in
occupying the time of the auditors in this theatre of anatomy and phy-
siology, by the details of such artificial helps to the recognition
of the outward characters of the members of the animal kingdom.

CLASSIFICATION OF ANIMALS. 11

But the principles on which animals are now grouped together are
of a different and much higher kind : they are the fruits of the best
results of the researches of all the great comparative anatomists since
the time of Linnaeus. The characters of the classes of animals have
been rendered by the immortal Cuvier, the highest expressions of
the facts ascertained in the animal organisation. I know not any
thing more calculated to impress the stranger to anatomical science
with the immensity of the labour that has been gone through, and
with the vast number of careful and minute dissections that have
been made, than the propositions which now form the definitions of
the primary groups of the animal kingdom.

The whole organisation of one species has been compared with that
of another, and this with a third, and so on, in order to ascertain in
what organ, or system of organs, the greatest number of animals w ould
be found to present the same condition : so that they might not be
arbitrarily, but naturally associated together. In the terms of logic, the
characters common to all animals having been ascertained, the ana-
tomist, in the next place, has sought to discover the difference, which,
added to the definition of animal, would form the most extended
species of that genus.

Aristotle thought he had found this differential or primary character
in the blood, recognising as blood only the circulating fluid, which
was red coloured. His first division of animals was accordingly into
Enaima and the Atiaima, or the sanguineous and exsanguineous ani-
mals. For a long time no advance was made beyond this early step
in the primary arrangement of animals. It was at length discovered
that many of the exsanguineous animals of Aristotle did actually
possess blood, though differing in colour from that of the so-called
sanguineous species. This led, however, only to a nominal improve-
ment in the classification ; the Enaima were called " red-blooded,"
the Anaima " white-blooded" animals. It was reserved for Cuvier to
discover, in the course of his minute dissections of the lower animals,
that an extensive class of worms had red blood circulating in a closed
system of arteries and veins ; and this discovery first materially affected
the value of the character applied by Aristotle to the primary groups
of the animal kingdom.

The Annelides, or red-blooded vv^orms, could not, however, be com-
bined with birds, beasts, and fishes, in a natural system, since they
differed from them so widely in almost every other particular of their
organisation.

Some other character was therefore sought for, since it became ob-
vious that the colour of the blood led to an artificial combination of
species. Lamarck thought he had discovered the desired character in

12

INTRODUCTORY LECTURE.

the vertebral colinmi, this structure being present in all the Enaima of
Aristotle, and absent in all his Anaima. Lamarck proposed, therefore,
the name of Vertebrata for the one class, and of Invertehrata for the
other. Now it will be observed that the In vertebrata are grouped
together by a negative character ;• and I know not any instance where
such a character has been employed in zoology, in which very differ-
ently organised species have not been associated together. What in-
deed can be predicated in common of the snail, the bee, and the polype,
than that they are animals, and have no vertebral columns, and the
like negations. It was obvious also that there was no proportion or
equivalency between the Vertebrate and the Invertebrate groups, and the
idea of equivalency or proportion, as well as that of likeness, ought
always to govern the labours of the classifier.

In the attempt to remedy this defect, the important discovery was
made that the vertebral column was subordinately related to a condition
of a much more important system in the animal body than the skeleton^
viz. the nervous system. Cuvier thereupon applied himself with inde-
fatigable industry to ascertain the arrangement of the nerves in the
Invertebrata, and after a long series of minute and elaborate dissections,
he discovered three modifications of that system, each of equal import-
ance with that which governed the vertebral character of the red-
blooded animals of Aristotle. Cuvier, accordingly, proposed to divide
the animal kingdom into four primary groups or sub-king-
doms, viz. Vertebrata.) Mollusca, Arficulata, and Radiata.

It is due to Hunter to state that the general results of
his dissections of the nervous system are expressed in the
definitions of the same leading types as those of Cuvier;
but he made the minor differences which he had detected
in the Vertebrate series equal to those primary types of the
nervous system which now characterise the 3Iollusca and
Articulata of Cuvier, — a view which would have led to
erroneous results if applied to the classification of the pri-
mary groups of animals.

The sub-kingdom Vertebrata, or Myelencephala, is cha-
racterised by the disposition of the principal mass of the
nervous system in a median axis, consisting of the brain
and spinal chord {fig- !•)? situated in the dorsal aspect of
the body, behind the heart and digestive system ; and in-
closed in a bony or cartilaginous case, constituting a verte-
bral column. The organs of the five senses, sight, hearing,
smell, taste, and touch, are almost always present.

The respiratory organs communicate with the pharynx, or
anterior part of the alimentary canal.

CLASSIFICATION OF ANIMALS.

13

J

The mouth opens in a direction parallel with the axis of the body,
is provided with two jaws, placed one above or in front of the other.
The blood is red.

The heart is a compact muscular organ,
having never fewer than two cavities, an au-
ricle and ventricle.

The muscles surround the bony or gristly
levers on which they act, or, in other words,
the skeleton is internal.

The locomotive members never exceed two
pairs.

The sexes are distinct.
In the sub-kingdom Molliisca^oY Heterogan-
gliata, the principal centre of the nervous
system bears the form of a ring, surrounding the gullet, from which
the nerves radiate, often unsymmetrically, to difFerent
parts of the body {Jig. 2.) : the brain is represented by
ganglions above («) or at the side {b) and below the gullet;
other ganglions (<? d) are developed in other parts of the
body. The form of the body corresponds with the dis-
position of the nervous system, and is commonly unsym-
metrical. In a single order {Cephalopods) the muscles
originate from an internal rudimental cartilaginous skele-
ton : in the rest they are attached only to the skin, which
forms a soft envelope in v/hich there are developed in
many species one or two calcareous plates, called shells.

The blood is colourless, or not red ; the heart compact,
muscular, and propelling the blood through a closed sys-
tem of arteries and veins.

The respiratory organ is never wanting ; and, with the
exception of one family (Ascidians)^ the cavity contain-
ing it communicates with or opens near the anus.
The Mollusca are dioecious or hermaphrodite.
The third primary division of the animal kingdom, viz.
the Articulata, has the brain in the form of ring, em-
bracing the gullet : a double ganglion above the tube
supplies the organs of sense : from the sub -oesophageal
ganglions two chords are extended along the ventral sur-
face of the abdomen, and are, in most species, united at
certain distances by double ganglions, which give origin
to the nerves of the extremities {Jig. 3.). From the sym-
metrical disposition of the nervous centres, I have called
this sub-kingdom Homogangliata. The body presents a

^\

A

14

INTRODUCTORY LECTURE.

corresponding symmetrical form. The skeleton is external, and
consists of articulated segments, of frequently an annular form : the
articulated limbs in those species which possess them have a similar
condition of the hard parts, in the form of a sheath, which encloses
the muscles.

The respiratory organs commonly open upon the sides of the body;
rarely near the anus, and never communicate with the mouth.

The jaws, when present, are lateral, and move from without
inwards, and not from above downwards.

The heart is situated in the back, is often vasiform ; and the veins
are frequently in the form of large, irregular sinuses ; there is always
a circulation, and the blood is red in one class (Anellides).
Most Articulata are dioecious : a few are hermaphrodites.
The Radiata, or fourth primary division of animals in the system
of Cuvier, is so called because most of the species comprising it have
their parts arranged around an axis, on one or several radii, or on
one or several lines extending from one pole to the other. The
nervous system, when traces of it have been visible, is also arranged

in radii {Jig. 4.). It does not
present the Homogangliate or
Heterogangliate type. In one
family only {Holothuriadce) is
there a distinct respiratory sys-
tem : the other characters as-
signed by Cuvier are negative
ones.

I have already observed, that
there is no instance in which
animals, grouped together by
negative characters, have formed
a natural assemblage ; nor is the
sub-kingdom Hadiata of Cuvier
an exception to this rule.
The truth is simply that the anatomy of this immense assemblage
of low-organised animals is not yet sufficiently understood; and, con-
sequently, general propositions, and at the same time positive ones,
like those which define the Vertebrate, Molluscous, and Articulate
sub-kingdoms, cannot be enunciated.

Much has unquestionably been done in this field of Natural
History since the time of Cuvier, and attempts have been made, with
various degrees of success, to subdivide the Radiata according to
positive characters.

CLASSIFICATION OF ANIMAtS. 15

The binary division, which I proposed in 1835*, has been adopted
in this country by my esteemed friend, the Professor of Comparative
Anatomy at King's College. I found that those Radiata of Cuvier
in which the nervous system could be most unequivocally traced in a
filamentary form, likewise presented an alimentary canal as a distinct
tube, with a mouth and anus, suspended in a distinct abdominal
cavity : the well-defined nerves governed a corresponding develop-
ment of the muscular system. Generation was by impregnated ova,
never by spontaneous fission or gemmation.

The Echinoderma, Rotifer a, Ccelelmi7ithay and Ciliobrachiatay are
the classes of Cuvier's zoophytes, which were grouped together
by positive characters, under the title Nematoneura,

I do not deny a filamentous condition of the nervous system in
the rest of the zoophytes ; each day brings with it testimony of its
presence in animalcules where it had not before been detected.
Nevertheless, in those classes in which the condition of the nervous
system is most obscure, we find that the digestive cavity is generally
excavated in the common parenchyma of the body, is devoid of free
parietes, and has no anal outlet : particular organs are often inde-
finitely multiplied, as the stomach in the Polygasfria, the generative
organs in the TcenicB, the prehensile mouth in the Polypi. Genera-
tion by gemmation and spontaneous fission is common in this lowest
division of the animal kingdom, to which I have applied the name
Acrita, which had been used in a more extended sense by Mr. Macleay.
Two classes, the Acalephce and Anthozoa (Ehrenberg), stand in an
intermediate position between the Acrita and Nematoneura ; and most
of the classes in the lowest division of the Radiata lead by more or
less gentle gradations into those of the higher one.

Nor is this surprising : the radiated animals are closely analogous
to the embryo forms of the higher classes ; and as the several changes
of such embryos succeed each other more rapidly than the later one,
so also each class of the Acrita more closely approximates some class
of the Nematoneura than is observed in the classes of the higher
groups, and the characters of the lowest or Acrite classes are the
least definite and fixed. I have, therefore, endeavoured to express
the relations of the higher and lower organised classes of the Radiata
of Cuvier, by placing them in parallel lines under their former col-
lective names, as in this tabular diagram of the provinces and classes
of the animal kingdom.

* Syllabus of the Lectures on Comparative Anatomy, given at the Medical School
of St. Bartholomew's. 8vo.

16

LECTURE II.

Sub-kingdom Articulata,
Class Crustacea.

Arachnida.

Insecta.

Anellata,

CiRRIPEDIA.

Kingdom ANIMALIA,

Sub-kingdom Veriehrala.

Class Mammalia.

AVES.

Reptilia.
Pisces.

Sub-kingdom Mollusca.
Class Cephalopoda.

Gasteropoda.

Pteropoda.

Lamellibranchiata.

Brachiopoda.

Tunicata.
Sub-kingdom Radiata.

Nematoneura.

Acrita.

Class Radiaria, Lamarck.

Echinoderma, Cuv.

ACALEPHA, Cuv.

Class Polypi, Cuv.

Ciliobrachiata, Farre. Anthozoa, Ehrenb. Nudibrachiata,

Farre.
Class Entozoa, Rudolphi.

Ccelelmintha, Owen. Sterelmintha, Owen,

Class Infusoria, Cuv.

Rotifer A, Ehrenb.

Polygastria*. Ehrenb.

LECTURE 11.

POLYGASTRIA.

I PROPOSE first to invite your attention to a class of animals, the most
minute and apparently the most insignificant of created beings. It
might almost seem needful to apologise for the design of trespassing
on your time and patience during one or two lectures with the
Anatomy and Physiology of creatures which are wholly invisible to
the naked eye. But* we are too apt to let our judgments of the im-
portance of objects be unduly influenced by first impressions, espe-
cially by those of magnitude or the contrary, which deeper insight
into their true nature and value rectifies.

The active atoms about to be described, for the knowledge of whose

* A Glossary and explanation of the scientific terms will be added to the con-
cluding Lecture.

POLYGASTRIA.

17

very existence we are indebted to the microscope, are by no means
the least complex of organised beings ; they belong, in fact, to the
higher division of organic nature, and manifest the distinctive pro-
perties of animals in the most striking and unequivocal manner.

If you skim a small portion of the gr^en matter, which in summer
time mantles the surface of a stagnant 'pool, place a drop of this in
the object-holder of a microscope, and examine it with a glass of a
quarter of inch focus, you will find it teeming with animal life; you
will see numerous little objects, of one or other of the forms, depicted
in this diagram, darting with rapidity across the field of view, or
gyrating or revolving on their axes. If you examine in like manner
a drop of water in which has been infused any vegetable or animal
substance, and which contains the particles of such substances in a
state of decay or decomposition, you will find such infusions similarly
tenanted with these active animalcules ; they have been termed from
this easy and common mode of procuring them, the animals of in-
fusion, or Infusoria.

The earlier microscopical observers confounded all the minute
living objects which they thus met with under that term ; but the
progressively increasing pains and discrimination of later observers
have removed the embryos of polypes, worms, and insects from this
motly and heterogeneous group, and have restricted it to those ani-
mals which, in their fully developed" states, manifest a form of body
devoid of radiated arms or tentacles, more or less amorphous, without
definite locomotive members, moving by means of minute superficial
vibratile cilia more or less diffused over the surface of the body, or
aggregated in circular groups near the head, where they produce by
their successive action the appearance of ra-
pidly rotating wheels. It is always the largest
species of Infusoria which are provided with
the last specified arrangement of vibratile
cilia, and these " wheel-animalcides," as they
are termed, being endowed with a higher
type of organisation, more especially of the
digestive system, constitute a distinct class of
Infusorial Animalcules, to which I shall refer,
after first noticing the anatomical characters
of the lower organised and more diffuselj^
ciliated group {fig- 5.).

The species of this group possess numerous

clear globular sacs in their interior, which

rapidly receive coloured nutriment, when in

a sufficiently subdivided state : these sacs are

c

Leucoplirys

18

LECTUK

described as stomachs by Ehrenberg, who has thence proposed for
this class the name of Polygastrica. The most minute forms, as the
species called Monas crepusculus, Ehr. have been estimated at the
^-_^i_^ of a line in diameter.* Of such Infusoria a single drop of
water may contain five hundred millions of individuals, — a number
equalling that of the whole human species now existing upon the
surface of the earth. But the varieties in the size of these invisible
animalcules are not less than that which prevails in almost every other
natural class of animals: — from the minutest Monad to the Loxodes or
Ampliileptus^ which are one fourth or one sixth of a line in diameter,
the difference of size is greater than between a mouse and an elephant.
Within such narrow bounds might our ideas of the range of size in
animals be limited, if the sphere of our observation was not aug-
mented by artificial aids.

Many of the polygastric animalcules are naked, covered only by a
delicate, transparent, and more or less ciliated integument. Others
are protected by a secreted shell, which consists of pure, colourless,
and transparent silex. This shell may present the form of a simple
shield, indicating by its position the back of the animal, as in Euplcea
Charon ; others have their flinty armour resembling a minute bivalve

shell : in some, as the Na-
viciday it has the form of an
elongated case, or flattened
cylinder, open at both ex-
tremities (^^.6.): it is some-

6

^^^^MlsMiiioyiWijiiijW®^^

Navicula.

times straight, sometimes bent like the Australian boomerang ; it
may present the form of a reticulated cone {fig. 7.), or a discoid
case \^fig. 8.) ; in short, the varieties of the silicious

shells of the Infusoria

surpass in number those

of the calcareous shells

of the Mollusca. But

whatever their forni,

the superficies of these
Dictyocha. dclicatc microscoplc

objects is generally sculptured with a beautiful, v/ell defined, and
more or less complicated pattern, which makes it easy to recognise
the species, and distinguish them from one another.

Most of these animated minims are locomotive and free ; a few, as tlie
Vorticellje, are attached to foreign bodies by a long and highly irritable
and contractile pedicle ; others, as the Gomjihoncma, are appended to
the extremities of the branches of a dichotomously divided stem.

Actinocyclus.

* A line is tlie twtU'ih oi an inch.

POLYGASTRIA. 19

The locomotive Polygastria propel themselves through the water by
the action of their vibratile cilia, which are sometimes generally dif-
fused, as in Bursaria and Nassula ; sometimes aggregated, in longi-
tudinal rows, as in Amphileptus ; often limited to the region of the
mouth, as in the Vorticellce, indicating the passage to the higher or
Rotiferous group. These cilia in some species, as in Stylo7iychia and
Euplotes, are of such relative size as to give the species a myriapodous
character, and are used, like little feet, to creep along the stems of the
CharUi and other minute vegetable plants. True jointed locomotive
members are never developed in any of this minute and primitive race
of animated beings ; but they retain, throughout life, those simple
vibratile cilia which produce the rotatory movements in the ova of
Mollusca whilst imprisoned in their nidus, which are probably the
agents of analogous movements of the ovum of the Mammalia in the
Fallopian tube, and which are doubtless common to the ova of all
classes of animals at that early period which the Polygastric Infusoria
seem permanently to represent.

These ciUa, the outward instruments of locomotion in Infusoria,
and which are retained in greater or less proportion on the epithelium-
clad mucous surfaces of all animals, appear, notwithstanding their
minute size and incalculable numbers, to owe their motions to the
actions of definitely arranged muscles : Ehrenberg has seen the ex-
panded base of the locomotive cilium in the Polygastria, and describes
the radiated structure which he conceives to indicate the disposition
of the muscular fibres moving such cilium.

If you watch the motions of the Polygastric Infusoria, you will
perceive that they avoid obstacles to their progress ; rarely jostle one
another; yet it is difficult to detect any definite cause or object of
their movements. Some species, it is true, prey upon animalcules of
their own class, and will gorge an individual of nearly their own
size, which they attract by the currents in the water caused by the
oral vibratile cilia. But the greater number of the class subsist on
the minute atoms of the decomposing animal and vegetable substances
of the fluids or infusions in which they exist, — particles which do
not require a definite pursuit, since they are inert and generally
diffused throughout the infusion.

The motions of the Polygastria have appeared to me, long watching
them for indications of volition, to be in general of the nature of
respiratory acts rather than attempts to obtain food or avoid danger.
Very seldom can they be construed as voluntary, but seem rather to
be automatic ; governed by the influence of stimuli, within or without
the body, not felt, but reflected upon the contractile fibre ; and
therefore are motions which never tire. We may thus explain the

c 2

20

LECTURE II.

fact which Ehrenberg relates — not without an expression of surprise
— namely, that at whatever period of the night he examined the
living Infusoria he invariably found them moving as actively as
in the day-time ; in short, to him it seemed that these little beings
never slept. Nor did this appear to be merely the result of the
stimulus of the light required to render them and their movements
visible ; since when they were observed upon the sudden application
of light without any other cause of disturbance, they were detected
coursing along at their ordinary speed, and not starting off from a
quiescent or sleeping state.

Evidence of muscular action in the Polygastria is afforded by the
contraction and change of form of the entire body. These changes
are so rapid, extensive and various in certain species that it is impos-
sible to refer their bodies to any definite shape : such form the genus
Proteus of Miiller, and the family AmcebcBci of Ehrenberg. No defi-
nite arrangement of nervous matter has yet been detected in the
Polygastric Infusoria ; but its presence is indicated by the coloured
eye-speck in certain genera: and nervous conductors of impressions
are no less requisite for reflex than for voluntary motions.

Every Polygastric animalcule, like every other true animal, has
a distinct mouth, which is sometimes placed upon a long extensile
neck, as in Lachrymaria ; in many of the monads it is provided with
a long tentacle or a pair of tentacles (y?^. 9. a.) ; in other species it is

armed with a curious dental ap-
paratus, consisting of a series of
long, slender and sharp teeth, ar-
ranged side by side, in the form
of a cylinder, as in Chilodon and
Nassula {Jig. 11. «, a).

If you remove some of these
animalcules from their native in-
fusion to a drop of clear water,
and, after they have fasted a few
hours, add a drop of the solution
of pure indigo or carmine, the
fine particles of these colours will
be greedily swallowed, and will
soon be seen to fill successively a
number of pyriform or spherical
cavities {fig. 5. b.) in the interior
of the animal. In some species these assimilative cells exceed 100 in
number, and if, with Ehrenberg, we call them stomachs, they afford
a very interesting example, in these early forms of animal life, of the
irrelative repetition of this most essential and characteristic organ of

Monad of Volvox.

POLYGASTRIA.

21

the animal. Ehrenberg has observed and figured certain definite
arrangements of these digestive sacculi, as well as of the alimentary
canal, to which he states that they are appended. In the Monads,
and many other of the more minute species of Polygastria, the sto-
machs are said to arise by separate tubular pedicles from the common
dilatable cavity of the mouth itself {^fig* 9. h^ b). Such species have
no intestine, no anus, and are said to be anenterous. In others, where
the sacculi are appended to an alimentary canal {^Polygastria en-
terodela Ehr.), that canal may be bent into a loop, and describe a
circle with the anus, opening near the mouth, as in Vorticella {Jig. 10.) ;

or it may pass in a straight line
through the axis of the body, as
in Enchelis ; or form several
flexuous curves in its passage
from the mouth to the opposite
extremity of the body, as in Lezi-
cophrys {Jig. 5.). But sometimes,
as in the Kolpodae, neither the
mouth nor anus is terminal in
position.

It has been objected to this in-
terpretation given by Ehrenberg
of the nature of the sacculi which
receive and assimilate the nu-
trient molecules that certain spe-
cies, as the Enchelis pupa, will
swallow another animalcule nearly equal to itself in bulk, and
thereby undergo a total change in the form of its body ; but this
may only imply great dilatability of the oesophagus or common canal,
such as we observe in the boa constrictor, which becomes in like
manner deformed after gorging a goat or other animal much thicker
than itself; doubtless the little sacculi successively receive and digest,
like the stomach of the boa, the dissolved parts of the swallowed
prey. Then again it is objected that the sacculi are not fixed in
definite positions, but are seen constantly, though slowly, moving,
and apparently rotating through the general cavity of the animal.
But the peristaltic wave-like undulations of a common connecting canal,
by drawing them successively in and out of the focus of the observer,
is quite sufficient and very likely to occasion the deceptive appearance
of their circulating movements. If these stomachs were actually
separate and closed sacs imbedded in the transparent gelatinous
plasma of the animalcule, and endowed with a circulatory movement,
it is inconceivable that they should commonly present the charac-

c 3

22 LECTURE II.

teristic arrangement which Ehrenberg has described and figured in
particular species ; as, for example, in the Vorticella, a circular
arrangement, or the wavy disposition in Leucophrys : yet such a
constancy in the arrangement of the assimilative sacs in these genera
is the result of my experience. Add to this, if they have not orifices
of communication with the alimentary tract, the difficulty of account-
ing for the rapid and ready transmission of the coloured aliment
into their interior without the surrounding parenchyme being stained.

It is possible that, besides digestive organs, the Polygastria may
have a vascular system for the conveyance of the assimilated fluid
throughout their frame; their minuteness ought to be no objection
to such a conjecture, for it is merely a relative idea. Probably the
reticular markings on the superficies of certain species may indicate
such vessels: it is certain that here is placed that mechanism for
renewing the surrounding oxygenised medium upon that surface,
which we find to be the essential respiratory dynamic of the gills in
most of the molluscous animals. At all events, to no other part of the
pbtygastric organism than to this ciliated superficies can the respiratory
function be attributed. But the action of the vibratile cilia upon
the water is necessarily attended in the free Infusoria with a reaction
which rolls the little animalcule through its native element and
produces the semblance of a definite voluntary movement.

Perhaps the most marvellous part of the organisation and economy
of the Polygastric Infusoria is that which relates to the function of
generation. This function, I may observe, is the only one which does
not necessarily require a special organ for its performance. I am
not aware that this proposition has been before enunciated, but it
will be quite intelligible when the essential nature of the generative
process is better understood.

Although both ovaria and testes have been unequivocally de-
monstrated in the Polygastria^ yet their most common mode of
propagation is quite independent of, and superadded to, the function
of these organs. In a well fed Monas, Leucophrys, Enchelys, or
Paramecium, the globular parenchyme may be observed to become a
little more opake and apparently more minutely subdivided : then a
clear line may be discerned stretching itself transversely across the
middle of the body and indicating a separation of the contents into
two distinct parts. The containing integument next begins to con-
tract along this line, and the creature to assume the form of an hour-
glass {fig, 11.) : this, tliough doubtless an uncontrollable, seems to be
a spontaneous action, and the struggle of each division to separate
itself from its fellow indicates an impulse in each to assume its
individual and independent character; the which they no sooner effect

POLYGASTRIA.

23

Nassula.

than they dart off in opposite directions, and rapidly acquire the normal
size and figure. In the Vorticella and some other species, we have

examples of spontaneous
division in the longitu-
dinal direction, which
commences at the mouth,
and extends to the irri-
table and contractile
stem, from which one or
both of the new formed
individuals detach them-
selves. In some species
this spontaneous fission,
which corresponds, as I stated in my Lectures on Generation in refer-
ence to the ova of the Medusa, in so interesting a manner with the
earliest phenomenon in the development of the ovum in the higher
animals, is arrested before its completion, but the partially separated
individuals continue in organic connection and form compound ani-
mals, sometimes in the form of long chains, sometimes branched,
sometimes expanding to form a spherical bag, as in the well-known
Volvox globator, which was long deemed a single individual of a
peculiar species. New spherical groups of Volvoces are throw^n off
into the interior of the parent monadiary,
which is rent open to allow them to escape,
as in^^, 12.

Another mode of generation is by gemma-
tion or the development of buds, which in
some species, as Cheromcij grow out of the
fore part of the body, and in others, as
Vorticella, from the hind part, near the stem,
or from the stem itself, from which the young
animal soon detaches itself. In most Vorticellidce, as in Carche-
sium and Episiylis, the small liberated end of
the body opposite the mouth is provided v. ith
a circle of vibratile cilia, so long as the in-
dividual swims freely : but these disappear
when the pedicle is developed.

With regard to the more common fissi-
^^^ parous mode, Ehrenberg has figured grada-
jV tiO'is of this spontaneous division of the or-
ganised contents of the integument in the
Gonhon (fig. 13.) and Chlamydomonas,
which may be compared with the earliest
c 4

Volvox.

^^ ^^

24 LECTURE II.

stages of the development of the germ, as figured by Siebold in the
Strongylus and Medusa, by Baer in the frog, and by Barry in the
rabbit. Dr. Martin Barry, who has discovered the very remarkable
and complicated nature of this process in the mammalian ovum, was
alone perhaps in the condition to fully comprehend and explain its
analogy to the fissiparous generation of the Polygastria, to which,
in 1840, I briefly alluded ; and this he has done in a paper, replete
with interesting generalisations, lately read before the Royal Society.
I have been favoured by that indefatigable observer with the following
notes of his ideas on this subject.

" Between the appearance presented by the mammiferous germ
during the passage of the ovum through the Fallopian tube, and those
met with in the young Volvox globator while within the parent, I find
a resemblance which is very remarkable indeed, extending even to
minute details. Not only do the cells of which the young Volvox is
composed form a body resembling a mulberry, with a pellucid centre,
but the cells gradually increase in number, apparently by doubling,
at the same time diminishing in size, like the cells of the mammi-
ferous germ ; which they resemble also in being originally elliptical
and flat.

" Some of the points of resemblance now mentioned were recog-
nised in the delineations of the Volvox given by Professor Ehrenberg ;
others were noticed during some observations I have myself made on
this very interesting microscopic object. Professor Ehrenberg has
figured five pellucid globules in a young Volvox just escaped from the
parent. These, the germs of another set, evidently resulted from di-
vision of the pellucid mass visible in an earlier state : so that here is
to be recognised fissiparous generation of the kind I have described
as reproducing cells.

'^ On examining the figures givenby Ehrenberg of successive genera-
tions of the Chlamydomonas (Jig.
14.), I see a resemblance to the
twos four, eight, &c. groups of
cells in the mammiferous ovum
\%mz^ } ^QQ striking, not to suggest that
the process of formation must be

Chlamydomonas. *

the same in both : the essential
part of this process consisting in division of the pellucid nucleus.
And it is deserving of remark, that Ehrenberg describes his Monas
hicolor evidently a nucleated cell, as possibly an early state of the
Chlamydomonas.

" The curiously symmetrical forms of many of the Bacillaria appear
to be due to this two, four, eight, &c. division of the nuclei of cells.

'^ The delineations of Goniumi Monas vivipara, and Ophrydium

POLYGASTRIA. 25

given by the great naturalist just mentioned, afford most satisfactory
examples of a pellucid globule, dividing and subdividing like the
hyaline in cells.

*' In many other of Ehrenberg's figures of the Polygastric Infusoria,
the corresponding part appears to me to be denoted by a blue, red, or
green colour, according as there had been added either indigo, carmine,
or sap-green. This accords with what has been mentioned in a former
page, regarding cells, namely, that a foreign substance becomes added
and assimilated through the hyaline.

" Fecundation of the ovum takes place in the same manner as nutri-
tion of the cell, and seems, in some instances at least, comparable to
the nutrition of one of the Infusoria.

" But farther, I recognise in Ehrenberg's delineations of the In-
fusoria, not merely a cell-formation, but everywhere the existence of
transitory or assimilative cells.

"^ And farther still : the infusorial cells, like the cells of the larger
organisms, have their origin in globules which become discs or " cyto-
blasts ; " these passing through stages such as those of ordinary cells.
Thus in Ehrenberg's Monadina are to be found, I think, the following
grades, perfectly analogous to the grades of cells : —

" 1. Globules and discs.

" 2. Discs with a pellucid point.

" 3. The point dividing.

" 4. Nucleated cells.

" 5. The nuclei dividing and thus giving origin to

" 6. Young cells, which are seen both within and escaped from
parent cells.

" There really seems to have been much truth in the remark long
since made by Oken, that animals are groups of bodies comparable to
the Infusoria. The cell is itself a little organism ; and cells coalesce
to form a larger one.

" The remarks just made respecting fissiparous generation, 1 appre-
hend, may be applied to gemmiparous reproduction, or propagation by
means of buds."

No doubt the minute Infusoria, which seem to have their develop-
ment arrested at the first or nearest stage from the primitive cell-
formation, offer close and striking analogies to the primitive cells
out of which the higher animals and all their tissues are developed ;
but the very step which the Infusoria take beyond the primitive cell-
stage invests them with a specific character as independent and dis^
tinct in its nature as that of the highest and most complicated
organisms. No mere organic cell, destined for ulterior changes in
a living organisation, has a mouth armed with teeth, or provided with

26 LECTURE II.

long tentacula ; I will not lay stress on the alimentary canal and
appended stomachs, which many still regard as " sub judice ; " but the
endowment of distinct organs of generation, for propagating their kind
by fertile ova, raises the Polygastric Infusoria much above the mere
organic cell.

In many of the larger species of Polygastria, radiated vesicles, sub-
transparent and colourless, generally two in number, and situated
near the two extremities of the body, of a highly irritable nature,
rapidly contracting and dilating, have been observed. Roesel first
figured this contractile vesicle in the Vorticella. In Euodon, in ad-
dition to these vesicles, Ehrenberg likewise discerned another organ,
of an oval shape, of a dull white colour, and of considerable size,
placed in the middle of the abdomen. It is easily detected by the
want of colour, when the animal has been w^ell fed and its stomachs
filled. This organ is regarded as the testicle, and the contractile
radiated bladders as the Vesiculce Seminales. The ovarium occupies
a more important share of the general cavity of the body : it fills all
the interspaces of the stomachs and intestine which are not occupied
by the male organs ; and consists of a number of minute corpuscules,
or nucleated cells, connected together in a reticulate form, generally of
a green or pink, or some other bright colour, in well-fed healthy Po-
lygastria.

The act of generation is attended with the destruction of the parent.
The ripe ova burst through some part of the abdominal integument,
and escape in a reticulated mass, together with the fertilising fluid.

By virtue of these diversified modes of multiplication, the powers
of propagation of these diminutive organised creatures may be truly
said to be immense. Malthusian principles, or what are vulgarly
so called, have no place in the economy of this department of
organised nature. To the first great law imposed on created beings,
" increase and multiply," none pay more active obedience than the
Infusorial animalcules.

Attempts have been made to calculate approximatively this rate of
increase.

On the 14th of November, Ehrenberg divided a Paramcecium aurelia,
a Polygastric animalcule measuring one twelfth of a line in length, into
four parts : which he placed in four separate glasses.

On the 17th of November, the glasses numbered 1 and 4 each con-
tained an isolated Paramaecium, swimming actively about. The
pieces in numbers 3 and 4 had disappeared.

On the 18th there was no change.

On the 19th each animalcule presented a constriction across the
middle of the body.

POLYGASTRIA. 27

On the 20th No. 1. had propagated five individuals by transverse
spontaneous division: inNo. 4. eight individuals had in like manner
been generated.

On the 21st no change had taken place.

On the 22d there were six nearly equal-sized individuals in No. 1.,
and eighteen individuals in No. 4.

On the 23d, the individuals were too numerous to be counted.

Thus it was demonstrated that this species of Polygastrian would
continue for six days without any diminution of reproductive force,
and that on one day a single individual twice divided, and one of its
divisions effected a third fission.

A similar experiment on a Stylonychia Mytilus, an animalcule one
tenth of a line in length, was attended with nearly the same results ;
it was supplied with the green nutrient matter, consisting of the
Monas pulvisculus, and on the fifth day the individuals generated by
successive divisions were too numerous to be counted.

And now you may be disposed to ask : To what end is this discourse
on the anatomy of beings too minute for ordinary vision, and of
whose very existence we should be ignorant unless it were revealed
to us by a powerful microscope? What part in nature can such
apparently insignificant animalcules play, that can in any way interest
us in their organisation, or repay us for the pains of acquiring a know-
ledge of it ? I shall endeavour briefly to answer these questions.
The Polygastric Infusoria, notwithstanding their extreme minuteness,
take a great share in important offices of the economy of nature, on
which our own well-being more or less immediately depends.

Consider their incredible numbers, their universal distribution,
their insatiable voracity ; and that it is the particles of decaying
vegetable and animal bodies which they are appointed to devour and
assimilate.

Surely we must in some degree be indebted to those ever active
invisible scavengers for the salubrity of our atmosphere. Nor is
this all : they perform a still more important office, in preventing the
gradual diminution of the present amount of organised matter upon
the earth. For when this matter is dissolved or suspended in water,
in that state of comminution and decay which immediately precedes
its final decomposition into the elementary gases, and its consequent
return from the organic to the inorganic world, "these wakeful
members of nature's invisible police are every where ready to ar-
rest the fugitive organised particles, and turn them back into the
ascending stream of animal life. Having converted the dead and
decomposing particles into their OAvn living tissues, they themselves
become the food of larger Infusoria, as the Hotiferri^ and of numerous

28 LECTURE III.

other small animals, which in their turn are devoured by larger
animals, as fishes ; and thus a pabulum, fit for the nourishment of the
highest organised beings, is brought back by a short route, from the
extremity of the realms of organic matter.

There is no elementary and self-subsistent organic matter, as BufFon
taught : the inorganic elements into which the particles of organic
matter pass by their final decomposition are organically recomposed,
and fitted for the sustenance of animals, through the operations of
the vegetable kingdom. No animal can subsist on inorganic matter.
The vegetable kingdom thus stands, as it were, between animal
matter and its ultimate destruction ; but in this great office plants
must derive most important assistance from the Polygastric Infusoria.
These invisible animalcules may be compared, in the great organic
world, to the minute capillaries in the microcosm of the animal body,
receiving organic matter in its state of minutest subdivision, and ^vhen
in full career to escape from the organic system, and turning it back
by a new route towards the central and highest point of that system.

LECTUEE III.

ROTIFERA.

The animal kingdom may be likened to a cone, the species of w^hich
it is constituted diminishing in number as they ascend in the scale of
complexity. Rising from different parts of the basal circumference,
the different groups reciprocally approximate, interweaving their
mutual affinities within a progressively closer reticulation, until they
finally culminate in the apex, which is crowned by Man.

The interest with which you listened to the anatomical details of
those minute creatures, which, by their low grade of structure, their
extensive distribution and incalculable myriads, form the base of the
animal pyramid, encourages me again to invite you to condescend
from the high sphere of your habitual studies and duties to this most
remote and lowly region of animal life.

Low though the Infusoria be, and remote from man in the scale of
organisation — literally at an invisible distance from us — yet, by the aid
of the optician's science and skill, analogies may be discerned in them
to the human structure, which ought to enlist your sympathies with
the discoveries that have been made in their Microscopical Anatomy.

KOTIFERA. 29

Time was, and not very long ago, in this country, when that term,
Microscopical Anatomy, was almost regarded as synonymous with the
anatomy of the imagination : but the numerous and highly important
discoveries which have been made and confirmed by observers in
almost every European state, by means of the greatly improved mi-
croscopes of the last ten years, have placed the value, the indispensa-
bility, of that instrument to the anatomist, beyond the necessity of
vindication.

Some scepticism may be natural and pardonable, when the anatomy
of an animalcule -y,voo of a line in diameter is attempted to bo
demonstrated: but trace it to its source, and you will find such
incredulity to be essentially based, not merely on distrust in our
means of observation, but in the difficulty of adequately conceiving
the relations of size. Just ideas of these relations are essential to the
acceptance and full appreciation of the discoveries which have extended
for us the bounds of space ; and I will ask permission to quote the
words of one of our old philosophers, which bear directly on this
subject, and, expressing a noble confidence in intellectual progress,
shed a prophetic gleam upon the present improved powers of pene-
trating space.

"In consistency, I suppose some bodies to be harder, others softer,
through all the several degrees of tenacity. In magnitude, some to
be greater, others less, and many unspeakably little. For we must
remember that, by the understanding, quantity is divisible into
divisibles perpetually. And therefore, if a man could do as much
with his hands as he can with his understanding, he would be able to
take from any given magnitude a part which should be less than any
other magnitude given. But the omnipotent Creator of the world can
actually from a part of any thing take another part, as far as we by
our understanding can conceive the same to be divisible. Wherefore
there is no impossible smallness of bodies. And what hinders but
that we may think this likely ? For we know there are some living
creatures so small that we can scarce see their whole bodies. Yet
even these have their young ones ; their little veins and other vessels,
and their eyes so small as that no microscope can make them visible.
So that we cannot suppose any magnitude so little, but that our very
supposition is actually exceeded by nature.

"Besides, there are now," (the book was published in 1655) "such
microscopes commonly made, that the things we see with them appear
a thousand times bigger than they would do if we looked upon them
with our bare eyes. Nor is there any doubt but that, by augmenting
the power of these microscopes (for it may be augmented as long as
neither matter nor the hands of M^orkmen are wanting), every one of

30 LECTURE 111.

those thousandth parts might yet appear a thousand times greater
than they did before. Neither is the smallness of some bodies to be
more admired than the vast greatness of others. .For it belongs to
the same Infinite Power as well to augment infinitely as infinitely to
diminish. To make the great orb, namely, that whose radius
reacheth to the sun, but as a point in respect of the distance between
the sun and the fixed stars ; and, on the contrary, to make a body so
little, as to be in the same proportion less than any other visible body,
proceed equally from one and the same Author of Nature. But this
of the immense distance of the fixed stars, which for a long time was
accounted an incredible thing, is now believed by almost all the
learned. Why then should not that other, of the smallness of some
bodies, become credible at some time or other ? For the majesty of
God appears no less in small things than in great ; and as it exceedeth
huitian sense in the immense greatness of the universe, so also it doth
in the smallness of the parts thereof. Nor are the first elements of
compositions, nor the first beginnings of actions, nor the first
moments of time more credible, than that which is now believed of
the vast distance of the fixed stars." *

I have said, that in the diminutive Polygastria, there might be
discerned structures analogous to our own. Vibratile cilia — their
sole organs of locomotion — are the first actively moving parts with
which the mammiferous ovum is endowed, with which, therefore, we
ourselves commence life. They are retained throughout life as an
essential part of the organisation of a very extensive tract of our in-
ternal mucous membranes ; and these most minute and incalculably
numerous vibrating filaments, like their analogues in the Pohjgastria,
know no repose.

It might almost have been anticipated that this earliest possessed,
and most extensively diffused, organical dynamic in every member of
the animal kingdom, should be the most conspicuous, and the sole,
moving power in the first-born of Fauna.

Is man liberated from one narrow spot in space, and enabled to
move to and fro on the surface of his little world, by virtue of an
internal receptacle of nutriment ? So, likewise, is the Infusorial animal.
Even some of the superadded complications of the digestive sac are
present ; the Polygastrian seizes food with tentacular lips, reduces it by
the action of a hundred dental spines, arranged, as we have seen, like
the teeth of the circular trephine : it is the very type of the digestive
function : assimilating and re-organising the decomposing particles of

* Thomas Hobbes, Elements of Philosophy, Molesworth's Ed. vol. i. p. 445.
8vo. London.

ROT IF ERA. 31

animal and vegetable matter with a hundred-stomach power. That
low delight, the bliss supreme of the civilised gourmand, is given
most liberally where it ought to be, to the creatures at the low^est
grade of animality.

Nor is the procreative function so abundantly or so variously en-
joyed by any other animal as in the Polygastria. At once fissiparous,
gemmiparous, and oviparous, the androgynous organs for the de-
velopment of the fertile ova were, as shown in the preceding Lecture,
of a sufficiently complicated character. In creatures whose most
obvious and common mode of propagation is by spontaneous fission,
a power so actively exercised, as, according to Ehrenberg's ex-
periments, to be productive of an incalculably rapid rate of multipli-
cation, it may be demanded : To what end were special organs of
generation developed ? Why should these fissiparous Polygastria be
provided with male glands, vesiculse seminales, and reticulated ovaria ;
with normal reproductive organs almost as complicated as in the
snail, which has no other mode of generation than by fertile ova ?
I am apt to think that the fissiparous reproduction has reference
principally to increasing the numbers of individuals in the infusions,
or receptacles of decaying organisms, in which they at that time
exist ; whilst the development of fertile ova has relation to future and
different localities or collections of such infusions, into which the ova
may be conveyed more easily than the entire animals, and so lay the
foundation of new^ generations of Infusoria. In the heats of summer,
for example, many of the pools and stagnant collections of w^ater in
which Infusoria abound are dried up. Now, it is true, that certain
Infusoria have the power of retaining their vitality for a long time in
a state of desiccated torpidity. I shall presently have to allude to
the experiments of Spalanzani and others on the wheel-animalcules,
in illustration of this curious property. Some who have repeated his
experiments have not succeeded in reviving the subjects after so long
a period of inanimation : nevertheless, great tenacity of life is un-
questionably, notwithstanding the delicate tissues of the Infusoria,
a property of creatures of their grade of organisation ; and what holds
good of the parent, in regard to this property of latent life, must, a
fortiori, be allow^ed to the ovuin.

Now the act of oviparous generation, that sending forth of countless
ova through the fatal laceration or dissolution of the parent's body,
is most commonly observed in tlse well-fed Polygastria^ which crowd
together as their little ocean evaporates ; and thus each leaves, by the
last act of its life, the means of perpetuating and diffusing its species
by thousands of fertile germs. When the once thickly tenanted pool
is dried up, and its bottom converted into a layer of dust, these in-

32 LECTURE iir.

conceivably minute and light ova will be raised with the dust by the
first pufF of wind, diffused through the atmosphere, and may there
remain long suspended ; forming, perhaps, their share of the particles
which we see flickering in the sunbeam, ready to fall into any
collection of water, beaten down by every summer shower into the
streams or pools which receive or may be formed by such showers,
and, by virtue of their tenacity of life, ready to develope themselves
wherever they may find the requisite conditions for their existence.

The possibility^ or, rather, the high probability, that such is the
design of the oviparous generation of the Infusoria, and such the
common mode of the diffusion of their ova, renders the hypothesis of
equivocal generation, which has been so frequently invoked to
explain their origin in new-formed natural or artificial infusions,
quite gratuitous. If organs of generation might, at first sight, seem
superfluous in creatures propagating their kind by gemmation and
spontaneous fission, equivocal generation is surely still less required
to explain the origin of beings so richly provided with the ordinary
and recognised modes of propagation. Many experiments have,
however, been detailed, in which adequate precautions appeared to
have been taken to prevent the possibility of the entry of fertile
germs into the fluid experimented on, after means had been taken to
destroy all that it might contain. From these experiments, the mere
access of atmospheric air, light, and heat to the infusions has been
deemed to include all the conditions required for the primary form-
ation of animal or of vegetable organisms. The results in favour of
such a view are, however, explicable by supposing that due pre-
cautions had not been adopted at the beginning of the experiment to
exclude every animal or germ capable of development in the infusion,
or to gain satisfactory assurance that the air subsequently admitted
contained nothing of the kind. The only experiment in which these
difficulties appear to have been fully overcome, is that in which the
requisite apparatus was conceived by Professor Schulze of Berlin.
He filled a glass flask half full of distilled water, in which were mixed
various animal and vegetable substances: he then closed it with a
good cork, through which were passed two glass tubes, bent at right
angles, the whole being air-tight : it was next placed in a sand bath,
and heated until the water boiled violently. While the watery vapour
was escaping by the glass tubes, the Professor fastened at each end
an apparatus which chemists employ for collecting carbonic acid :
that at the one end was filled with concentrated sulphuric acid, and
the other with a solution of potash. By means of the boiling heat, it
is to be presumed that every thing living and all germs in the flask
or in the tubes were destroyed ; whilst all access was cut off by the

ROTIFERA. 33

sulphuric acid on the one side, and by the potash on the other. The
apparatus was then exposed to the influence of summer light and
heat ; at the same time there was placed near it an open vessel, with
the same substances that had been introduced into the flask, and also
after having subjected them to a boiling temperature. In order to
renew constantly the air within the flask, the experimentor sucked with
his mouth several times a day the open end of the apparatus, filled
with the solution of potash, by which process the air entered his
mouth from the flask through the caustic liquid, and the atmospheric
air from without entered the flask through the sulphuric acid. The
air was of course not at all altered in its composition by passing
through the sulphuric acid in the flask ; but all the portions of living
matter, or of matter capable of becoming animated, were taken up by
the sulphuric acid and destroyed. From the 28th of May until the
beginning of August, Professor Schulze continued uninterruptedly
the renewal of the air in the flask, without being able, by the aid of
the microscope, to discover any living animal or vegetable substance;
although, during the whole of the time, observations were made
almost daily on the edge of the liquid ; and when, at last, the Pro-
fessor separated the different parts of the apparatus, he could not
find in the whole liquid the slightest trace of Infusoria or ConfervcB^
or of mould ; but all three presented themselves in great abundance
a few days after he had left the flask standing open. The vessel
which he placed near the apparatus contained on the following day
Vibriones and Monads^ to which were soon added larger Polygastric
Infusoria^ and afterwards Rotifera.^ To the organisation of this
higher form of Infusoria, which are always the last to appear in
infusions, I now proceed.

The Hotifera are so called on account of the aggregation of their
cilia into circular or semicircular groups upon lobes or processes of
the head, which resemble rudiments of the ciliated tentacles of the
higher or Ciliobrachiate Polypes.f By the vibration of these cilia, which
occasions the appearance of little wheels in rapid motion, strong cur-
rents are produced in the surrounding water, and they thus serve as
the instruments for locomotion and the prehension of food. The body
in the Hotifera is more or less elongated or vermiform. It is provided,
at its posterior extremity, with a pair of slender and pointed claspers,
pi'otected by a sheath, into which they can be retracted when not in

* This experiment was quoted from the Edinburgh New Philosophical Journal.
Vol. xxiii. p. 165. Pi. 1. fig- 2. gives a representation of the simple and effectual
apparatus devised by Prof Schulze. W.W. C.

f Ehrenberg remarks that the Hotifera are " Bryozoa without the power of pro-
pagating by gemmation." — Die Infiisionsthierchen, fol. 1838, p. 384.

34

LECTURE III.

use. These appendages are longer than the body in some species, as
the Notommata Tigris : their sheath is much elongated and slightly
anniilated in the Brachioni : it is telescopiform in Scaridiiim : both
claspers and sheath are wanting only in the AimrcEus. The integument
of the body is smooth, and never ciliated : although the parasitic jointed
fibres of HygrocrociSi which attach themselves sometimes to the in-
tegument of the larger species, as ISotommata centrura, give it that ap-
pearance. The PolgarthrcB have long jointed filaments, like the rays
of a fish's fin, attached to the sides of the body.

Not any of the species are known to secrete a silicious shell ; but
many of them are provided with a transparent gelatinous case, into
which they can contract their bodies ; thus off'ering another analogy
to the Ciliobrachiate Polypes, and also to the bivalve-sheathed Ento-
mostraca. The loricate genera are Noteus, Anurcea, Brachionus^ and
Pterodina. In all the species the shell is a cylinder or case {testula),
not a mere shield (^scutelluni).

Horn-like processes project from the front margin of the shell in
some species of Brachionus, and from both front and back margins in
other species. In some Notei and Anurcece the shell is ornamented
by large pentagonal or hexagonal groups of granules.

The cephalic cilia are aggregated into from two to five groups, upon
lobes (Jig- 15, «.), which sometimes are developed into short tentacular
processes, with a verticillate arrangement of cilia, as mStephanoceros,
These lobes or processes Ehrenberg regards as muscular. The

movements of the ciliated quasi-
wheels are under the control of
the will. They can be instantly
arrested, the whole apparatus
drawn out of sight, again pro-
truded, and as instantly set in
motion. The muscles which pro-
trude and retract of the ciliated
lobes, which bend and modify the
form of the body, and which
throw out, attach, or heave in the
anal anchors, are developed in
the form of distinct fibrous fas-
ciculi. You perceive in this dia-
gram, for example (fig. 15.), the
Notommata. rctractors of the oral cilia and of

the anal forceps ; the long and narrow longitudinal muscles (Z>, 6),
which shorten the whole body ; and their antagonists the transverse

KOTIFERA. 35

bands (c, c), which diminish the breadth of the body and restore its
length.

With this advanced condition of the muscular system the parts of
the nervous system now likewise become distinctly visible. Ehren-
berg delineates a large cerebral ganglion, which in some species is of
a trilobate form, in close connection with the coloured, generally red,
ocellus or eye-speck (e.). Some of the nervous filaments extend from
this ganglion forwards to the muscular lobes supporting and moving
the wheel-like cilia ; other filaments of greater length stretch back-
wards into the cavity of the body, apparently attached to the ventral
integument, on the outer side of the principal longitudinal retractor
muscles.

In Notommata clavulata, Ehrenberg describes two radiated gan-
glions in the neck (d, d), superadded to the principal cerebral ganglion
connected with the rotatory muscle, and other gangliform bodies on each
side, developed upon the long abdominal nervous filaments. Besides -
these, other small enlargements are figured as ganglions upon the
transverse bands or vascular circles of Ehrenberg, making altogether
eight pairs of ganglions in this little animalcule, which measures one
eighth of a line in length. With regard to the ganglions on the
transverse vessels, both these and the vessels bear a striking analogy
to those transverse muscles, with a middle swelling, which Dr. Arthur
Farre* has described and figured in his Ciliobrachiate Polypes.

The movements of the Rotifera are of a more varied character than
those in the Polygastria ; they sometimes dart swiftly forwards ; at
others glide leisurely along, or, anchoring themselves by their little
terminal claspers, employ their ciliated paddle-wheels to create the
currents which prove so fatal to the minuter race of Infusories.
When the Rotifer has attached itself to some fixed body by its hinder
claspers, the vortices which it occasions in the water are so directed
as to draw the smaller Infusoria and other particles of food towards
the orifice of the mouth.

Having seized their prey, it is exposed in the pharynx (/) to the
destructive action of a complicated dental apparatus (fig. 16,/). This
consists of two jaws, acting horizontally upon a median piece, or anvil.
The hard maxillae are each bent upon themselves at a right, or, rather,
acute angle ; the transverse or dental part, which beats upon the
surface of the anvil, being divided into two or more sharp spines.
The muscles which work these dental hammers are inserted into
the longitudinal portion, which may be regarded as the rudimental

♦ Philos. Transact. 1837.
D 2

36

LECTURE III.

jaw. The efficacy of these instruments in tearing to fragments the
objects swallowed may be easily discerned in the living animal
through its transparent parietes.

The condition of the alimentary canal is very similar in most of the
genera, which are chiefly distinguished thereby from the Polygastric
Infusoria, It is a more or less simple tube {Jig. 15, «7), extending longi-
tudinally through the well-developed abdominal cavity, to terminate by
a cloacal outlet (Ji) at the hinder end of the body, generally above the
base of the sheath of the claspers. It is sometimes wider, sometimes
narrower, sometimes with and sometimes without a constriction indi-
cative of the stomach {Jig. 15, g) : in Rotifer {Jig.16.)
and Ptyura there is a distinct terminal dilation or rec-
tum ; sometimes the intestine is complicated with many
caeca, as in Diglena and Megalotrocha. Most of the
species have, just behind the pharynx, or continued
from the stomach, two large oval glandular sacs, rarely
cjdindrical or bifurcated, to which sometimes fila-
mentary caeca are appended, as in Enteroplea. These
secerning sacs {Jig. 15, i) may discharge the office of
liver or salivary glands.

Ehrenberg recognises a vascular system in the pa-
rallel transverse slender bands which surround the
body ; these are in close connection with the integu-
ment. With more probability we may regard as san-
guiferous organs the free longitudinal vessels, likewise
indicated by Ehrenberg, on the dorsal aspect, which
are connected with a fine vascular network near the
mouth, and which send filamentary tubes to the intestine.

The wheel-like organs, by rapidly changing the oxygenated fluid
which bathes their surface, may be supposed to take the most potent
share in the respiratory function. But Ehrenberg directs our attention
to some peculiar ciliated vibrating oval corpuscules, which are attached
to the free seminal tubes on each side the abdomen ; and to which cor-
puscules he assigns the name of internal gills. The water essential to
the respiratory function discharged by these problematical bodies, and
by the vascular surfaces of the viscera, is admitted into the interior of
the body by an opening in the neck, which, in very many species, is
prolonged upon one or two spear-shaped tubes, which are beset with
vibratile cilia : the water is observed to pass to and fro in streams
through these tubes. It consists of an expanded part and an ap-
pendage ; the expanded part consists of three folds or vesicles ; the
vibrating appendage resembles a crotchet in music.

The Rotifera are androgynous : most of the species are oviparous.

ROTIFERA. 37

the ova being large and few in number : a few are ovo-viviparous.
The fertilising principle is formed in and by two long and slender
tubes (^Jig. 15, A, ^), commencing each by a blind extremity at the ante-
rior part of the abdominal cavity, and extending with a few slight
folds to the neck of a single large spermatic vesicle, which communi-
cates with the oviduct in the cloaca. The essential organ of the male
apparatus is thus manifested under its most simple form, as a single
tuhidus in each testis^ in these small animals. The singleness of the
vesicula, which is characterised by the same remarkable irritability as
the two contractile vesiculae of the Polygastria^ accords with the ab-
rogation of the fissiparous property in the Rotifera.

The egg-forming organ consists of a simple wide sac, single in
Notommata {fig- 15, I), but more commonly divided into two cornua,
the body terminating by a short contracted cervix, which communi-
cates with the cloaca. There can be no doubt about the proper func-
tion of this conspicuous viscus, for the structure of the ovum can be
discerned through its transparent walls ; and, in the Rotifer vulgaris,
the young may be seen to escape from the eggs in the uterus, and leave
the empty shells behind them : they issue from the parent after in-
tervals of from five minutes to an hour.

In the Hydatina senta Ehrenberg carefully traced the development
of the ova and embryons. The ova are first manifested as clear spots
or vesicles filled apparently with albumen. In two or three hours a
dark speck is seen in the middle of the clear vesicle, which he com-
pares with the yolk. In five or six hours the yolk fills the dear space
and pushes it to one side, and in this state the ova are fecundated
and excluded from the cloaca.

The change in the position of the clear spot is important, from its
interesting analogy with the change in the position of the germinal
vesicle in relation to the yolk of the rabbit's ovum, and with the
altered position of the entire ovum in relation to the ovisac, pre-
paratory to impregnation ; both being, to use Ehrenberg's expression,
" pushed to one side ; " to that side, viz. which approximates the im-
portant vesicle or cell whence all subsequent development radiates,
to the aperture which admits the fertilising principle.

Ehrenberg states that in the ovum of the Hydatina, three hours
after its exclusion, the clear spot (germinal vesicle) has disappeared,
and the egg is occupied by the yolk, which is granular at one end
and clear at the other. A dark spot then appeared in the middle of
the ovum, which, six hours after exclusion, could be distinguished as
the head with the rudimental dental aj^paratus of the embryo. At the
eleventh hour the wheel-like ciliated organs began to play, and the

D 3

38 LECTUKE III.

fcjetus to move in the egg. At the twelfth hour the body was com-
pletely formed, and bent somewhat spirally, the bifurcated anal ap-
pendage being doubled backwards towards the head. The re-
volutions of the young Rotifer are now so powerful as to threaten
every instant to burst the egg-shell, but they often continue two
hours.

The average period of development of a young Hydatina under
favourable circumstances is twenty-four hours ; twelve within and
twelve without the parent's body. When it proceeds more slowly,
Ehrenberg recommends the liberal supply of the green monads
(^Chlaynydomonas ptilvisculus, and JEugle?ia viridis).

Ova deposited in the cold early days of winter remain undeveloped
until spring, and are protected by their dense double shell.

Ehrenberg watched during eighteen days successively an individual
Hydatina senta, which was full-grown when singled out, and did not
die of old age, which proves this species to live more than twenty
days. Such an individual is capable of a four-fold propagation every
twenty-four or thirty hours, bringing forth in this time four ova,
which grow from the embryo to maturity, and exclude their fertile
ova in the same period. The same individual, producing in ten days
forty eggs, developed with the rapidity above cited, this rate, raised
to the tenth power, gives one million of individuals from one parent?
on the eleventh day four millions, and on the twelfth day sixteen
millions, and so on.

Although this rate of production from fertile ova is the greatest
hitherto observed, far exceeding that in the class of insects, it is much
inferior to the propagative power in the Polygastria. We saw that
in the Paramceciwn aurelia, which lives several days, a transverse
fissure took place, the individual becoming two every twenty-four
hours. It also propagates by ova, which are excluded not singly,
but in masses ; which ova rapidly develop and repeat the acts of pro-
pagation ; so that the possible increase in forty-eight hours is quite
incalculable. Who can wonder that infusions should, with the brood
of two or three days only, swarm with these animalcules I

All the ordinary Infusoria live through the winter beneath the ice.
After having been once completely frozen, Ehrenberg found them
dead when thawed. They, however, manifest considerable powers of
resistance to this effect of extreme cold. Ehrenberg endeavoured to
freeze some Infusoria in a watch-glass, and examined the clear ice in a
cold room : he observed that those which appeared to be frozen and im-
bedded in the mass were actually inclosed in very minute vesicles in
the ice. He conceives that they may remain torpid in this state

KOTIFERA. 39

through the winter, and revive when their little ice-houses have been
melted away in spring.

Infusoria are destroyed generally by expanding and bursting, after
a few minutes' subjection to the heat of boiling water.

In water subjected to a galvanic current strong enough to cause de-
composition, the contained Infusoria are killed. When subjected to a
weaker current, those only which came into its course were affected :
some Rotifera were observed to be stunned only, and afterwards re-
covered ; others were killed.

Tenacity of life is a very striking physiological character of the
Infusoria,

The famous phenomena of the revival of Rotifera^ after having
been completely dried and apparently killed, certainly when reduced
to the state of the most complete torpidity, \vere first observed by
Leeuwenhoek in the year 1701. The father of microscopical anatomy
had been engaged in examining some specimens of Rotifer vulgaris
with Euglena sangiiinea, and had left the w^ater in which they were
contained, to evaporate. Two days afterwards, having added some
rain-water, which he had previously boiled, within half an hour he
saw a hundred of the Rotifera revived and moving about. A similar
experiment was followed with the same result after a period of five
months, during which period the Rotifera had remained in a state of
complete desiccation and torpidity. These observations were re-
peated by Baker and J. Hill. You will find all the experiments
that were recorded before the time of Haller accurately quoted in his
great '' Physiologia Corporis Humani," vol. viii. p. 111. Fontana kept
Rotifera two years and a half in dry sand, exposed to all the power
of an Italian summer's sun : yet in two hours after the application of
rain-water they recovered life and motion.

Goze, Corti, and Miiller record similar experiments ; but those
performed by the celebrated Abbe Spallanzani are perhaps most
generally known.

He succeeded in reviving his Rotifers after four years' torpidity :
he alternately dried and moistened the same animalcules twelve times
with similar results, except that the number of the revivers was suc-
cessively smaller ; after the sixteenth moistening he failed to restore
any of them to life.*

One of the essential conditions of the revival of the Rotifers
appeared to Spallanzani to be their burial in sand : the access of air
seems prejudicial to their retention of vitality. Miiller, the famous

* Opusc. die Fis, Anim. vol. ii. p. 181.
D 4-

40 LECTURE III.

Danish observer of Infusoria, only succeeded in reviving them when
they were surrounded by foreign particles, and defended from the
air. Both Oken and Rudolphi deny the revival of desiccated
animals ; but later observers have succeeded in producing the won-
derful phenomena described by Spallanzani, especially Professor
Schultze ; and I myself witnessed at Freiburg, in 1838, the revival of
an Arctiscon which had been preserved in dry sand by the Professor
upwards of four years.

I have already, at the close of the previous lecture, alluded to the
important functions, apparently so disproportionate to their size and
powers, which the Polygastria perform in relation to the conservation
of organic matter and of the purity of the atmosphere. They like-
wise take their share in modifying the crust of the earth. It has
been shown that some Polygastria are naked, others loricated or
defended by silicious shells, of definite and easily recognisable forms
and patterns in different species. Prof. Ehrenberg had not long made
these observations before he discovered that a certain kind of sili-
cious stone, called Tripoli or Polierschiefer, was entirely composed
of such cases; was in fact the debris of Polygastric Animalcules,
chiefly of an extinct species, called Gaillonella distans. The sub-
stance alluded to has long been well known in the arts, being used in
the form of powder for polishing stones and metals. At Bilin, in
Bohemia, there is a single stratum of this substance, not less than
fourteen feet thick, forming the upper layer of a Tripoli hill, in every
cubic inch of which layer Ehrenberg estimates that there are forty-
one thousand millions of individuals of the Gaillonella distans. It
likewise contains the shells of NaviculcE, Bacillaria^ ActiJiocyclus,
and other silicious animalcules. The lower part of the stratum con-
sists of the skeletons of these animalcules, united together without
any visible cement ; in the upper and more compact masses the in-
fusory shells are cemented together, and filled by amorphous silicious
matter, formed out of dissolved cases. Corresponding deposits of
the silicious cases of these animalcules have since been discovered in
many other parts of the world, some including fresh water, others
marine species of Infusoria. A quantity of a pulverulent matter is
deposited upon the shores of the lake near Uranea in Sweden, and
which from its extreme fineness resembles flour. This has long been
known to the poorer inhabitants under the name of Berg-mehl, or
mountain meal, and is used by them mixed up with flour as an article
of food : it consists almost entirely of the silicious shells of pulverised
Polygastria. Most of the infusorial formations, as the polishing slates
of Cassel, Planitz, and Bilin, are, in fact, extraordinary monuments,
which have handed down to us the record of the existence of Poly-

ROTIFERA. 41

gastric Infusoria at remote periods of the history of the earth ; and
they are much more extensive, and will be more durable, than the
proudest mausolea by which Egyptian kings have endeavoured to
perpetuate the memory of their existence.

In another point of view the Polygastric Infusoria are highly re-
markable. Their extremely minute size, simplicity of structure,
tenacity of life, and extraordinary powers of reproduction, have
enabled them to survive, as species, those destroying causes which
have exterminated all the higher forms of animals. Several species,
for example, still exist, which were in being at the period of the de-
position of the chalk, and which contributed their silicious remains to
the flinty masses which are always more or less intermixed with cre-
taceous matter. Before this discovery no remains of higher-organised
animals at present in existence had been detected, with the same degree
of certainty, in the cretaceous formation. A few existing zoophytes
andtestacea first make their appearance in the tertiary beds immediately
above the chalk ; hence called, by Mr. Lyell, Eocene, from eog, the
dawn, as indicating the first dawn of the creation of existing species.
The number of existing species of shells increases in the Miocene,
and is still greater in the Pliocene tertiary strata; but the higher
animals, as the Anoplotheria, Palceotheria, Mastodotis, Mammoths^
and other mammalian contemporaries of the Eocene, Miocene, or
Pliocene testacea, have utterly perished. The discovery, therefore,
by Ehrenberg, of several, at least twenty, species of silicious- shelled
Infusoria, fossil, in the chalk and chalk marls, which are perfectly
identical with those from the sands of the Baltic and North Sea, is a
most interesting addition to the obscure history of the introduction of
the successive species of animals on this planet, and must add greatly
to the interest of this Infusorial class in the eyes of the naturalist and
geologist. " For these animalcules/' says Ehrenberg, " constitute a
chain, which, though in the individual it be microscopic, yet in the
mass is a mighty one, connecting the organic life of distant ages of the
earth, and proving that the dawn of the organic nature coexistent
with us reaches farther back in the history of the earth than had
hitherto been suspected."

The still existing species are by no means rare or isolated, but fill
in incalculable numbers the seas of Northern Europe, and are not
wanting on the tropical coasts of the globe. With reference to
the operations of the invisible Polygastria at the present day on
these and other coasts, I have only time to refer you to the translation
of a late paper by the indefatigable Berlin professor, entitled, " Ob-
servations upon the important Part which Microsco])ic Organisms
play in the choking up of the Harbours of Wismar and Pillau ;

42 LECTURE IV.

also, in the Formation of the Mud which is deposited in the Bed
of the Elbe at Cuxhaven, and upon the Agency of similar Phe-
nomena in the Formation of the Bed of the Nile, at Dongolar, in
Nubia, and in the Delta of Egypt." * " Truly, indeed," says Ehren-
berg, "^ the microscopic organisms are very inferior in individual
energy to lions and elephants, but in their united influences they are
far more important than all these animals."

LECTURE IV.

ENTOZOA.

The ancient philosophers styled man the microcosm, fancifully con-
ceiving him to resemble in miniature the macrocosm or great world.

Man's body is unquestionably a little world to many animals of
much smaller size and lower grade of organisation, which are
developed upon and within it, and exist altogether at the expense of
its fluids and solids.

Not fewer than eighteen species of internal parasites, or of those
which infest the internal cavities and tissues of the human body, have
been enumerated ; and of these, at least fourteen are good and well
established species of Entozoa.

Hippocrates and Aristotle had distinguished the human intestinal
worms by the names of " Helminthes stronguloi" and " Helminthes
plateiai ; " but the study of these parasites in general has been re-
served for recent times. Since the time of Linnaeus the stimulus
which that great master gave to every branch of Natural History has
been in no department more potent than in encouraging researches
into the before neglected field of the Internal Animal Parasites.

To the labours of Bloch, Goeze, Zeder, and, above all, to those of
Rudolphi, we are indebted for our knowledge of these animals as an
extensive class^ which Rudolphi has characterised, under the name of
Entozoa, as white-blooded worms without respiratory organs, and
(but less accurately) without nerves.

The number of these Parasites may be conceived when it is stated
that almost every known animal has its peculiar species, and generally
more than one, sometimes as many as, or even more kinds than, infest
the human body.

* Edinb. Philos. Journal, vol. xxxi. p. 386

ENTOZOA. 43

There are few common and positive organic characters which can
be attributed to this very extensive and singular group of animals :
they have generally a soft, mucous and colourless integument, which in
a few species is armed with spines. That the integument should be
uniformly white or whitish might, a priori, have been expected of
animals which are developed and exist in the dark recesses of other
animal bodies. The mature ova are almost the only parts which
naturally acquire a distinct colour ; and the subtransparent body some-
times derives other tints from the accidental colour of the food. Ex-
cluded also by the nature of their abode from the immediate influence
of the atmosphere, no distinct respiratory organ could be expected to
be developed in the Entozoa; but this negative character is common to
the Entozoa with most of the other Radiata of Cuvier. In creatures
surrounded by and having every part of their absorbent surface in con-
tact with the secreted and vitalised juices of higher animals, one might
likewise have anticipated little complexity and less variety of organ-
isation. Yet the workmanship of the Divine Artificer is sufficiently
complicated and marvellous in these outcasts, as they may be termed,
of the Animal Kingdom, to exhaust the utmost skill and patience of
the anatomist in unravelling their structure, and the greatest acumen
and judgment in the physiologist in determining the functions and
analogies of the structures so discovered. What also is very re-
markable, the gradations of organisation that are traceable in these
internal parasites reach extremes as remote, and connect them by
links as diversified, as in any of the other groups of Zoophyta, although
these play their parts in the open and diversified field of Nature.

Beginning with the lowest link we have to commence with a con-
dition of organisation more simple than is presented by the lowest
Infusory or Polype. We end with a grade of organisation, which,
whether it is to be referred to the radiated or articulated types,
zoologists and anatomists are not yet unanimous.

Amongst the vermiform animals with colourless integument, co-
lourless circulating juices and without respiratory organs, two leading
differences of the digestive system have been recognised : in the one
it is a tube with two apertures contained in a distinct abdominal
cavity ; in the other it is excavated or imbedded in the common
parenchyme of the body, and has no anal outlet. The first condition
characterises the Vers Intestiiiaux Cavitaires of Cuvier ; the second
the Vers Intestinaux Parenchymateux of the same naturalist.

I have rendered the Cuvierian definitions of the two leading
classes or groups of the Entozoa by the names "• Coelelmintha," and
" Sterelmintha."

44

LECTURE IV.

The cavitary worms of Cuvier include the cylindrical species or
round worms which form the order Nematoidea of Rudolphi.

This great entozoologist, who devoted the leisure of a long life
to the successful study of the present uninviting class, divided the
parenchymatous Entozoa into four other orders. The Acanthocephala,
in which the head has a retractile proboscis armed with recurved
spines, the body round and elongated, and the sexes in distinct indi-
viduals. The Trematoda, in which the head is unarmed and has a
suctorious foramen, the body rounded or flattened, and generally one
or more suctorious cavities for adhesion, and in which the organs of
both sexes are in the same individual. The Cestoidea, in which the
body is elongated, flattened, and generally articulated. The head,
variously organised, is generally provided with suctorious cavities and
a central mouth, sometimes armed with a coronet of hooks, some-
times with four unarmed or uncinated tentacles. Both kinds of genera-
tive organs are combined in the same individual. Lastly, the order
Cystica, in which the body is rounded or flattened, and terminates
posteriorly in a cyst, which is sometimes common to many indi-
viduals. The head is provided with suctorious cavities; and the
mouth, with a circle of hooklets, or with four unarmed or uncinated
tentacles. No distinct generative organs are developed in the cystic
Entozoa.

The anatomy of the Entozoa is so distinct in each of these orders
that I shall describe it successively in a few typical species, selecting
more especially for demonstration those M'hich infest the human body ;
and which chiefly concern the medical practitioner.

In this category the common pathological product, called ' Acepha-
locyst ' by Laennec, is by many received, and ought not, perhaps, in
this place to be omitted . The acephalocy st (Jig. 1 7> ^) consists of a sub-
globular or oval vesicle filled with
fluid. Sometimes suspended freely in
the fluid of a cyst of the surrounding
condensed cellular tissue (a) ; some-
times attached to such a cyst ; de-
veloping smaller acephalocysts, which
are discharged from the outer or the
inner surface of the parent cyst.
These acephalocysts vary from the
size of a pea to that of a child's head. In the larger ones the wall of
the cyst has a distinctly laminated texture. They are of a pearly
whiteness, without fibrous structure, elastic, spurting out their fluid
when punctured. Their tissue is composed chiefly of a substance
closely analogous to albumen, but differing by its solubility in hydro-

Acephalocj'st.

EXTOZOA. 45

chloric acid ; and also of another peculiar substance analogous to
mucus.* The fluid of the acephalocysts contains, according to
Lobstein, a small quantity of albumen with some salts, including
muriate of soda, and a large proportion of gelatin.

The tunic of the acephalocyst is usually studded with more or less
numerous and minute globules of a clear substance (c), analogous to the
" hyaline," whose remarkable properties in reproductive cells, Dr.Barry
has recently described, and from which the young acephalocysts are de-
veloped. No contractile property, save that of ordinary elasticity, has
been observed in the coats of the acephalocyst ; no other organisation
than that which I have just described ; no other function than that of
assimilation of the surrounding fluid by the general surface, and the de-
velopment of new cells from the nuclei of hyaline. We see with how
little reason such a body can be compared with the Volvox gl abator y as
has been done by Professors Nitzsch and Leiickart.f The discovery of
the composite character of that low organised Infusory and the elucida-
tion of the anatomy of each constituent monad prove the acephalocyst
to stand on a still lower step in the series of organic structures. A
better comparison is that which approximates the acephalocyst to the
Protococci of the vegetable kingdom ; these lowest forms of crypto-
gamic plants consisting of a simple transparent cyst, and developing
embryo cysts from their external surface. The knowledge that we
now possess of the primitive embryonic forms of all animals and of
all animal tissues, places us in the position to take a true view of the
nature of the acephalocyst. It seems to me to be most truly de-
signated as a " gigantic organic cell," not as a species of animal, even
of the simplest kind.

Yet these productions have not escaped the ingenuity and dis-
criminative powers of the classifier. Of the numerous species,
nominal or real, which are to be found in the works of naturalists
and pathologists, I shall notice only two: — 1st, the Acejyhalocystis
Endogena of Kuhn, likewise called Socialis, vel prolifera^ by Cru-
veilhier : the " Pill-box Hydatid " of Hunter. It is the kind most
commonly developed in the human subject, and in which the
fissiparous process takes place usually from the internal surface of
the parent cyst, the progeny being sometimes successively included :
and, 2dly, the Acephalocystis Exogena of Kuhn, Eremita, vel Sterilis,
of Cruveilhier, which developes its progeny generally from the external
surface, and is found in the ox and other domestic animals.

And now I can well imagine that some may be tempted to ask,

* Collard, Diet, de Med. et de Chir. prat. Art. " Acephalocystes."
t Tschudi, Die Blasenwurmer, 4to, 1837, p. 29.

46 LECTURE IV.

having heard this description of a free and independent being, whose
tissues are chemically proved to be of an animal nature, imbibing
nourishment without vascular connection with the cavity containing
it, and reproducing its kind, how is an animal to be defined if this be
not one? The answer that the acephalocyst has no mouth may,
perhaps, not be regarded as satisfactory. Definitions apart, our
business is to discover to what organic thing the acephalocyst is
most analogous.

The primitive forms of all tissues are free cells, which grow by
imbibition, and which develope their like from their nucleus of
hyaline. All the animal tissues result from transformations of these
cells. It is to such cells that the acephalocyst bears the closest
analogies in physical, chemical, and vital properties. When the
Infusorial Monads are compared to such cells, and man's frame is
said, by a figure of speech, to be made up of such monads, the
analogy is overstrained, because no mere organic cell has its mouth,
its stomachs, its testes, and ovaria. So also it appears to me that
the analogy has been equally overstrained, which makes the acepha-
locyst a kind of monad, or analogous species of animal. We may,
with some truth, say that the human body is primarily composed or
built up of acephalocysts ; microscopical, indeed, and which, under
natural and healthy conditions, are metamorphosed into cartilage,
bone, nerve, muscular fibre, &c. When, instead of such change, the
organic cells grow to dimensions which make them recognisable to
the naked eye, such development of acephalocysts, as they are then
called, is commonly connected in the human subject with a lowering
of the controlling vital energies, which, at some of the weaker points
of the frame, seem unable to direct the metamorphosis of the
primitive cells along the right road to the tissues they were destined
to form, but permits them to retain, as it were, their embryo con-
dition, and to grow by the imbibition of the surrounding fluid, and
thus become the means of injuriously aff'ecting or destroying the
tissues which they should have supported and repaired.

I next proceed to consider the internal parasites, which present
the characters assigned by Rudolphi to his Cystic Entozoa.

The name Echinococcus is given to a cyst resembling the acepha-
locyst, when, in addition to the sero-albuminous fluid, it contains a
number of microscopic organised beings, floating, or freely swimming
in it, or adhering by special prehensile organs to the internal surface
of the cyst. They are quite independent of the acephalocyst, which
merely forms their place of abode ; and to them I would limit the
generic name Echinococcus^ which indicates one of their organic
characteristics, namely, a coronet or cylinder of spines, which

ENTOZOA. 47

surrounds their mouth. In the Echinococcus Veterinorttm, the
species which infests the common domestic animals, the oral spines,
when retracted, offer a close resemblance to the cylinder of teeth,
which characterises the Nassula {fig. 11.) and many other Poly-
gastria. The body of this Echinococcus likewise presents a number
of clear globules resembling hyaline, and very similar to the
so-called stomachs of the Polygastria. In an acephalocyst, from
the abdomen of a recently killed hog, I observed these little creatures
moving in the fluid, apparently by the action of superficial vibratile
cilia, thus adding a remarkable feature to their resemblance to the
Polygastria. The Echinococch from a small musk-deer, lately dis-
sected at the College, closely resemble those of the hog, which I
have elsewhere described * ; but, being dead, the ciliated structure is
not indicated, and could not be detected. Each tooth or spine
presents an elongated triangular form, a small process extending from
the middle of its outer margin, probably for the attachment of the
protractor fibres.

The Echinococci of the human subject {Jig. 18.), which have been
accurately described by Professor Miiller in a case where
they were developed in the urinary bladder, and which
have been carefully figured by Mr. Quekett in a case ob-
served by Mr. Curling, where they were developed in the

Echinococcus *' • i i • n

hominis. liver, wcrc in both cases inhabitants of a cyst, rather the
parasites of an acephalocyst than of the human body. These Echi-
nococci differ from those of the hog in having suctorious cavities (b),
external to the circle of teeth («), and thus closely resembling the
head of a Taenia, appended to a small cyst.

The hydatid developed in the substance of the brain of sheep and

rabbits, called CcBnurus cerebralis, consists of a large cyst, with which

many heads, like those of the Taeniae, are in organic connection.

19 These can be retracted within, or protruded without, the

common cyst.

The genus Cysticercus is characterised by having only
a single uncinated and suctorial head, connected by a
neck or body, sometimes annulated, and of greater or less
length, with the terminal cyst. Of this genus one species,
Cysticercus Celluloscc (Jig. 19.), is occasionally developed in
the human subject. It has been met with in the eye, the brain, the
substance of the heart, and the voluntary muscles of the body. The
peculiar inflammation which it excites leads to the formation of a

* Art. " Entozoa," Cyclopcedia of Anatomy and Physiology, p. 1 58.

48

LECTURE IV

condensed bag of cellular tissue around it. The cysts are oval, and
generally about half an inch in length. The most common hydatid
in the ox and other ruminants, is a large species of the present genus,
called Cysticercus tenuicollis. All these Cysticerci manifest their
affinity with the Cestoidea by the organisation of their head. A
species not uncommon in cysts in the liver of the rat and other
rodents, completes the transition to the Cestoidea, by having the
terminal bladder of small relative size, and the body
of great length, and divided into joints or segments.

I proceed next to consider the organisation of the
tapeworms, as the Cestoidean entozoa are commonly
termed ; and for this purpose I shall select the two
species which infest the human intestines, namely, the
Tcenia solium and the Bothriocephcdus latus, and
which may be regarded as the types of the two lead-
ing genera of the order.

The TcEnia solium is the only species which is
likely to fall under the notice of the British medical
practitioner. It appears to be the only species of
tapeworm developed in the intestines of the natives
of Great Britain ; and it is equally peculiar to the
Dutch and Germans, The Swiss and Russians are
as exclusively infested by the Bothriocephalus latus.
In the city of Dantzig, it has been remarked, that
only the TcEnia solium occurs ; while at Konigsberg,
which borders upon Russia, the Bothriocephalus latus
prevails. The inhabitants of the French provinces
adjoining Switzerland are infested with both species.
The Tcenia solium attains the length of ten feet
and upwards : it has been observed to extend from the
pylorus to within seven inches of the anus. Its breadth varies from
one fourth of a line at its anterior part {Jig. 20.), to three or four lines
towards the posterior part of the body, which
then again diminishes. The head is small, and
generally hemispherical, broader than long. The
mouth is situated on a central rostellum, which is
surrounded by a double circle of small recurved
hooks {Jig.^l, a). Behind these are four suc-
torious cavities {Jig.2\i b), by which the head is
firmly attached to the intestinal membrane. The
anterior segments are feebly represented by trans-
verse rugae; the succeeding ones are subquadrate,
and as broad as long. They then become sen-

Head and neck,
Taenia solium.

.w>.

'^]

d,i

Taenia solium.

ENTOZOA. 49

sibly longer, narrower anteriorly, thicker and broader at the pos-
terior margin, which slightly overlaps the succeeding joint. The
last series of segments are sometimes twice or three times as long
as they are broad, proportions which are never ob-
served in the Russian tapeworm. But the chief dis-
tinction between the Bothriocephalus latus and the
Tcenia solium is in the position of the generative orifices;
which, in the Tcenia solium, are placed near the middle
of one of the margins of each joint, and are generally
alternate (Jig> 22, «, a).

The integument of the Taenia is soft, like a mucous
membrane; beneath it is a layer of delicate transverse
muscular fibres, and a more easily recognisable stratum
of longitudinal fibres.

Taenia solium. m i •

The condition of the nervous system is a matter
of analogical conjecture. Its principal part, no doubt, exists in, or
near, the well -organised head ; where, as in the Trematoda, it may
form a ring round the gullet, and send backwards two delicate fila-
ments. The correspondence of the digestive system with that of many
Distomata, may be stated with certainty. The alimentary tube, com-
mencing at the minute central mouth, soon bifurcates ; and each di-
vision is continued as a slender unvarying canal throughout the
whole length of the worm, near the margin of the segments : the
two longitudinal canals are connected together by transverse canals,
one of which is situated at the posterior margin of each segment.
The longitudinal nutrient canals have no communication with the
marginal pores : they equally exist in those Cestoidea which have no
marginal pores.

The tissue of the Taeniae in which the alimentary canals are im-
bedded, is beset with numerous minute nucleated cells. These doubt-
less take an important share by their assimilative and reproductive
powers in the general nutrition of the body.

The Taeniae are androgynous, and each joint contains a compli-
cated male and female apparatus equal to the production of thousands
of impregnated ova. The ova are developed in a large, branched
ovarium {Jig.2% c), occupying almost the whole space included by the
nutrient canals, at least in the posterior segments, where it is very con-
spicuous from the amber colour of the more mature ova. The oviduct
is continued from near the middle of the dendritic ovary to the mar-
ginal papilla, where it terminates by a small orifice posterior to that of
the male organs. The parts of the male apparatus which have at pre -
sent been recognised, consist of a small pyriform vesicle (^fig. 22, b),
situated near the middle of the posterior margin of the segment ; thi.-?,.

E

50 LECTURE lY.

however, is most probably only a seminal vesicle, and not the testis.
The vas deferens is continued from the vesicle with slight undu-
lations, to the middle of the segment, where it bends upon itself at a
right angle, and terminates at the generative pore {fig. 22, a), from
which the lemniscus, or rudimental penis, projects. The ova may be
fecundated by intromission of the lemniscus into the vulva before they
escape.

The segments containing the mature ova are most commonly
detached and separately expelled. The development and metamor-
phoses of the embryo Teeniae have not yet been completely traced
out. In the Tenia serraia and other species in which the embryo
has been observed, the head is first formed and is provided with six
hooks ; it rotates in the ovum, doubtless by means of superficial vi-
bratile cilia.

For a knowledge of the minute anatomy of the Bothriocephalus latus
{figs. 23, and 25), we are indebted to the admirable skill and patience of
Professor Eschricht, of Copenhagen, whose work* on the subject has re-
ceived the prize of the Academy of Sciences, at Berlin. His observa-
tions were made on a specimen of the worm, which, after various re-
medies, was dislodged from one of his patients.

In Denmark, as in Holland, the Tcenia solium is the common tape-
worm; but the case in question occurred in a female aged twenty-three,
born at St. Petersburg, of Russian parents ; who had spent almost all
her childhood and youth at Copenhagen, with, however, occasional so-
journs of three or four months' duration, in Russia. The usual symp-
toms of tapeworm, with occasional ejection of fragments, occurred in
ISS^. She had also distorted spine and other indications of a weakly
constitution. Thrice, in that year, oil of turpentine with castor oil,
and once some strong drastic pills and pomegranate rind, were adminis-
tered ; and, with the exception of the last medicine which produced
no eflTect, each time from twelve to twenty feet of the worm were ex-
pelled, but without the head. In the spring of 1835, she was induced
to try a remedy called '^ Schmidt's cure," which consists of strong
coff'ee, and salt herring ; and it was followed by the expulsion of a
piece of the worm measuring ten yards, still without the head. She
then paid a visit to Petersburg, and there parted with four or five
pieces of the tapeworm measuring from two to four feet in length.
She returned to Copenhagen in the winter of 1835, still suffering from
her pertinacious parasite. Castor oil and turpentine were again ad-
ministered on the 3d of December, and procured the ejection of two
pieces of the tapeworm, measuring together twelve feet in length, but

* Anatomisch. Physiologische Untersuchungen iiber die Bothryocepbalen. 4to.
1840.

ENTOZOA.

51

without the head. Eighteen days afterwards, NoufFer's
remedy, which consists of a preparation of fern seed,
was resorted to, whereupon the remaining part of the
worm, twenty feet in length, with the neck and head,
came away, and ail the symptoms of the malady disap-
peared, and had not returned in 1838, when this instruc-
tive case was recorded.

The head and neck are represented in this diagram
{fig- 24.). You will see that it closely resembles the
figure which Bremser first gave of this important and
characteristic part of the broad tapeworm. Instead of
the coronet of hooks and circle of suckers which cha-
racterise the head of the Tcenia solium, it forms a simple,
elongated, sub-compressed enlargement, with an anterior
obtuse prominence, perforated by the mouth {Jig. 24, a),
and having two lateral sub-transparent parts separated
by a middle opake tract. According to Bremser, the
margins are slightly depressed, forming what are termed
the Bothria or pits {Jig. 24. b, b), whence the generic
name of this tapeworm. There was no trace of joints
within two inches and a half of the head. These are at
first feebly marked ; then the segments expand posteri-
orly, and slightly overlap the succeeding ones : their
Head and neck length nearly equals their breadth. At sixteen inches
Bothr. latus. from the head a slight prominence at the middle line,
and near the anterior part of the ventral surface of the segment,
24 indicates the genital apertures. These become conspic-

uous in the posterior segments, and are two in number,
situated pretty close together on the same prominence
(Jig. 25.).

The tegumentary and muscular systems appear to re-
semble closely those in the Tcenia solium. Dr. 2-5
Eschricht could not discern any trace of nerves*
Of the nutrient system, he obtained evidence
only of the two submarginal longitudinal ca-
nals : by placing the recent segments in dilute
acetic acid, he coagulated the contents of these
canals, which were then manifest by their opa-
city and whiteness. They were doubtless filled
with the chyle of the unfortunate sufferer.
How the chyle is absorbed by the Bothrio-
cephalus Eschricht was unable to discern : he supposes,
Bothr. latus. analogically, by an anterior suctorious mouth, leading to

E 2

Bothr. latus.

52 LECTURE IV.

a gullet, which bifurcates in the neck to form the two longitudinal
canals. Eschricht could not detect the transverse anastomosing
canals. We shall be justified, perhaps, by the analogy of this species
of Bothriocephalus from the Python *, in which I succeeded in
injecting with quicksilver both the longitudinal and transverse canals,
in concluding that the anastomosing channels are present at the
posterior margins of the segments in the Bothriocephalus of the
human species.

Innumerable and very minute nucleated cells are apparently dis-
seminated through the tissue of the Bothriocephalus. Eschricht
points out their analogy to the blood-cells in the lower animals, but
could not perceive any ramified system of blood-vessels.

At the deepest part of each segment there is a stratum of whitish
granules or glands {Jig. 26. «, «), composed of a cluster of minute blind
26 sacculi, filled with opake fluid, each

^ Jk '] J ^^^.^ j_,.^ group or gland being suspended in a

I' ""' ^^^^^^^p^^^^^!^^^^. separate cell, the pedicle of which is,
, without doubt, the duct of the saccu-

r tated gland which Eschricht regards

\_,^^N^ as a testis, and estimates at 400 in

. — ' "^'^"'^^"^ " ^— ^ number at each joint. Their ducts
Bothr. latus. unite to fomi a network, having

the capsules of the gland in the interspaces. The vas deferens
(Jiff' 26, b) is best seen on the dorsal aspect of the joint, along
the middle of which it runs in close transverse folds, progressively
increasing in breadth, until it terminates in a pyriform seminal re-
ceptacle or " bursa penis " (Jff. 26, c). From this bursa a small
lemniscus is protruded through the anterior of the two generative
pores, situated upon the eminence near the middle of the anterior
part of the ventral surface of the segment.

The ovaria (Jig. 26, d) are situated near the posterior margin of the
segment. They consist of two large transversely oblong lobes, and a
smaller median annular portion. They are composed of tubes in which
the small germinal and vitelline rudiments of the ova are arranged in
rows. The oviducts terminate in a long tubular uterus (Jiff. 26, e),
which is considerably wider than the vas deferens, and advances for-
wards, making many transverse convolutions, the two last being wider
than the rest, and extending on each side of the bursa penis. The ducts
of a very complicated series of glands communicate with the uterus
before its final termination at the vulva or pore, which is behind the
male opening. The glands just alluded to form a stratum next

* Prep. No. 846. A.

ENTOZOA. 53

beneath the skin at the sides of the joints. Eschricht calculates that
there are 1200 of these glands in each joint. In the joints furthest from
the head, containing the mature ova, these glands become filled with
a thick yellow matter which they pour into a system of ramified
ducts, which unite to discharge themselves in the dilated part of the
uterus. Their office seems to be to cement together the ova in hard
cylindrical masses by forming a crust around them, in which state
they are found in the detached joints. This is the first example
' which we have yet seen of nidamental glands, which we shall sub-
sequently find a conspicuous part of the generative organs in many
oviparous Invertebrata.

From this description it will be 'seen that the proportions and
almost the forms of the ovarium and testis, are reversed in the
Bothriocephalus and T(Enia : the positions of the sexual outlets
are unquestionably very different in the two genera. Both, how-
ever, agree in presenting the most extensive development and pre-
ponderance of the generative system that is known in the Animal
Kingdom. In fact there is scarcely space left in the hinder joints
of the tapeworms for the organs of any of the other systems.

The natural rate of life of a tapeworm, the consequences to the
remaining adherent part, of the repeated detachment of the ovi-
gerous segments, the extent to which they are detached and subse-
quently renewed, have not yet been, nor are likely ever to be, the
subjects of direct observation in these internal parasites of man.

Some highly interesting facts have, however, been made known by
the same professor to whom we are indebted for a knowledge of the
anatomy of the Bothriocephalus latus, in the economy of another
species of Bothriocephalus which is extremely common in the small
sea-fish called Cottus scorpius.

During midsummer, these tapeworms are fully developed, and
their segments are laden with ova. They adhere by the fore part of
the head to the mucous surfaces of the appendices pyloricse, and cast
off the ovigerous segments, sometimes in their whole length ; so that
headless tapeworms are found in the lower part of the intestine,
whilst a number of heads without bodies may be observed adhering
to the pyloric appendages between other tapeworms of very different
lengths. The heads thus left behind generate a new series of perfect
joints in the following way : the joint next the head is divided by a
transverse fissure into two, each of which repeats the same process
as soon as it is somewhat grown. Whilst the joints multiply in this
way, they continue to increase in size, and so become removed from
the head ; but at a certain distance from the head, this mode of sub-
dividing ceases, and the whole nutritive power is applied to the de-

E 3

54 LECTUKE IV.

velopment of the organs of generation. During winter the Bothrio-
cephalus punctatus, still adhering firmly to the mucous surface of the
pyloric appendages, grows to its full length, and the generative organs
are formed ; but no ova can be seen. These begin to appear at the
commencement of spring in the posterior joints, and by degrees fill
the uteri of all the joints, until they occupy those which are close to
the head, when the separation from the head before described en-
sues, and this last-named member is left to repeat the important
process.

No single joint of a tapeworm can develope a head, and form a
new individual ; the transverse fission relates only to the dissemination
of the fertile ova, from which alone new TcBiiice. are developed.

The hypothesis of equivocal generation has been deemed to apply
more strongly to the appearance of internal parasites in animal bodies
than to the origin of animalcules in infusions. But if a tapeworm
might be organised from a fortuitous concourse of organic particles,
or by the metamorphoses of an organic cell in the animal it infests,
why that immense complication and extent of the organs for the
production of normal fertile ova ?

" The division of the body into joints is intended," as Professor
Eschricht well observes, " to produce a corresponding number of
bunches of ova, just as the repeated ramification of plants is destined
to provide space for the production of new bunches of seeds." The
head of the tapeworm is fixed to the mucous surface, and thence it
derives the nutritive juices required for the whole organism ; in the
same manner as the root procures the nourishment of the plant from
the soil. The ova having reached maturity, the joints rupture to
liberate them ; or the whole joint will be thrown off" in the same way
as the seeds of plants are freed, sometimes one by one, sometimes in
masses, according to the particular manner of life assigned to every
species of plant. " And is there any one," asks Dr. Eschricht, " who,
upon the contemplation of this wonderful apparatus, and the ex-
traordinary results of its agency, can for a moment imagine that it is
without an object or an end?"

The geographical distribution of the human Cestoidea is, likewise,
opposed to the doctrine of their spontaneous origin. The organic
particles, or alimentary mucus of a Swiss and Dutchman, are not so
distinct in their nature as to account for the difi'erence in their tape-
worms. A native of one of these countries may be infested by the
tapeworm peculiar to another region, if he sojourn there, just as
the English sailor may be attacked by the Guinea- worm, if he visits
the tropical regions where that entozoon is common.

The great anatomist Soemmering suffered from a Bothriocephalus

ENTOZOA. b6

latus. Now he was a German ; but it was ascertained that he paid
occasional visits to a friend in Switzerland, There, doubtless, the
germ of the parasitic worm was introduced into his body. The count-
less ova of the taeniae, with their hard crusts or shells, and tenacity
of latent life, are, doubtless, widely dispersed, and need only the
accidental introduction into an appropriate nidus for ulterior develop-
ment.

LECTUEE V,

ENTOZOA.

The essential anatomical character of the third order of Entozoa in
the classification of Rudolphi may be represented by combining the
head of an unarmed Taenia, with one of its joints, containing the fully
developed androgynous organs. The digestive system would then be
represented by a simple bifurcating canal, each fork ending in a cul
de sac.

The Trematoda may be characterised as having a soft, rounded, or
flattened body, with an indistinct head, provided with a suctorious
foramen, and having generally one or more sucking cups for adhesion
in different parts of the body ; the organs of both sexes are in the
same individual.

The great entozoologist Rudolphi, a pupil and ardent admirer of
Linnaeus, adopted external and easily recognisable characters for the
generic subdivisions of the Trematode order, the species of which were
distributed according to the number and positions of the suctorious
orifices and cavities. When there is a single one, it constitutes the
genus Monostoma : when there are two, which are terminal or at
opposite ends of the body, you have the character of the genus
Amphistoma : when the posterior of the two suckers is not terminal,
but on the inferior surface of the body, this constitutes the genus
Distoma : three suctorious cavities characterise the genus Tristoma;
five, the genus Pentastoma ; and a greater number that called Poly-
stoma. Subsequent anatomical investigations have led to the forma-
tion of other genera of Trematoda, and have likewise shown that
those species which were grouped together by the external and arti-
ficial characters of the Rudolphian system, manifest differences of
organisation, indicating, at least, the generic distinction of such
species : nay, most of the Pentastomata of Rudolphi appertain to the
Coelelminthic class of Entozoa.

£ 4)

56

LECTURE V.

Dist. hepaticurn'
nat. size.

1 am compelled to limit ray illustrations of the anatomy of this
order almost to the two species which infest the human subject ;
these are the Distoma hepaticurn {Jig. 27.) and the Distoma lanceo-
latum (Jig. 28.). Both are peculiar to the biliary
ducts and gall bladder, but may pass thence into the
intestine. Both, likewise, are more commonly found
in the ordinary domestic animals, as the sheep and ox?
than in the human subject.

A full-grown Distoma hepaticurn is of a flattened,
ovate, or oblong-ovate form, broader and rounded
anteriorly, attenuated posteriorly ; from ten to sixteen
lines in length, from four to seven in width % the broad
end sends forward a sort of conical neck or head,
convex above, flat below ; one of the suctorial acetabula {a) is at the
extreme apex of this process^ a little turned downwards ; the other (6)
is at the under part of the body, at the base of the neck : the first sucker
is perforated by the mouth ; the posterior and larger one is imperforate,
and serves merely as an organ of adhesion. You will observe, also, a
small depression {d) between the characteristic suckers, in which the
genital pores are placed : not unfrequently the curved or spiral penis
may be observed projecting from the anterior of these orifices.

The body is of a whitish yellow colour, variegated near the margins
by the yellow ova, and on the dorsal aspect by the brown colour
of the double ramified alimentary tube. The integument is soft :
traces of muscular fibres can hardly be discerned, except around the
larger subventral sucker.

Dr. Mehlis, who has given the best anatomical account of the
human Trematoda^ describes and figures the nervous system of the
Distoma hepaticurn as a delicate oesophageal filamentary ring, with a
slight ganglionic enlargement on each side, from which minute fibres
pass into the suctorial sphincter ; and two large filaments pass back-
wards, one on each side, as far as the ventral sucker.

I have tested this description by a dissection of the largest known
species of Distoma, the Dist. clavatum, whose anatomy I have de-
scribed in the Zoological Transactions. You may distinctly perceive
in this dissection the oesophageal nervous circle, the small cephalic
filaments, and the two widely separated nervous chords of the trunk.
In this specimen also, you will see the integument raised as a distinct
membrane from the outer transverse muscular fibres, and a portion
of these is reflected from the inner longitudinal stratum. Feeble
analogues of these parts of the muscular system are doubtless pre-
sent in the smaller Distomata of the human subject.

The sole aperture of the alimentary system is that of the anterior

ENTOZOA.

57

pore, which is surrounded by the fibres of the suctorial organ.
The alimentary canal is continued from this pore for a very short
distance as a single tube, and then bifurcates ; the divisions {fig. 27.
c, c) diverge to enclose the bursa penis and the ventral sucker, again
approximate, and afterwards run parallel with each other, with a nar-
row interspace, along the middle of the body to the caudal extremity.
At their first bend, each tube gives off three or four branches from
its outer, but none from its inner side. The parallel tubes send off a
few short and simple branches from the inner side, and many larger
ramified branches from their outer sides, which terminate in blind
extremities near the margin of the body.

These canals seem, at first sight, to be simply excavated in the
substance of the body ; but, attentively examined, they present a
delicate proper tissue. They are usually filled with a brownish
chyme, which appears to be mucus stained with cholesterine.

A more minute system of ramified tubes, which by some have been
regarded as the nutrient vessels, commences by a small foramen at the
caudal extremity of the body. The trunk of this system runs forwards
with a serpentine course, along the interspace of the forked alimentary
canal, to the middle of the body, where it terminates in many finely
ramified branches. It seems to represent, therefore, an excretory
rather than a nutrient system.

The vascular system of Diplostomum volvens, so beautifully illus-
trated by Nordmann, is surely the equivalent of the excretory system
of capillaries, described by Mehlis in the Distoma hepaticum ; and the
median trunk, which is compared by Nordmann to the dorsal aorta in
the Anellides, must be the principal excretory conduit : it passes
directly backwards to the terminal pore, distinctly recognised by
Nordmann in the Diplostomum as an excretory outlet ; and he does
not positively deny, what his figures indicate, its continuity with the
straight duct terminating at that pore. In the Dist. clavatum I have
shown that the excretory system is complicated by a large terminal
receptacle or bladder, of which the hinder pore is the outlet.*

The male organs of the Distoma hepaticum consist of the se-
cerning seminal tubes, a vesicula seminalis, a penis, and its bursa :
the convoluted tubuli testis equal the smallest branches of the
alimentary canal in size ; they occupy a great extent of the middle
part of the body, are inextricably interwoven, are recognisable by
their opaque white colour, and terminate by two trunks in a common
canal, which ends at the base of the receptaculum penis. This

* Zool. Trans. 1. p. 41. fig. 18. g.

58

LECTURE V.

28

appendage is spirally disposed when flaccid, is tubular, and distinctly-
perforated at the apex.

The ovaria occupy the whole margin of the body for a line in
breadth : they consist of minute, branched tubes, in which the ova
are developed, as in acini. The oviducts are close to the ventral
integument, and terminate in a single large uterine canal, which is
disposed in many convolutions between the subventral acetabulum and
the bursa penis : it terminates by a vulva, or distinct pore, immedi-
ately behind the male bursa. The ovarian ova are colourless and
pellucid, but become opaque as they approach the oviduct : having
entered this tube they acquire a white glistening tunic, and after-
wards a yellow colour, which becomes deeper as they approach the
vulva.

The Distoma lanceolatum {Jrg. 28.) has been regarded as the young
of the Distoma hepaticum ; but it is of a different form,
has a different anatomical structure, particularly as re-
gards the alimentary canal, and its title to rank as a
distinct species is sufficiently vindicated by its power
of developing fertile ova without changing its cha-
racteristic shape or increasing in size. It rarely equals
five lines in length, but is more commonly three lines
long ; flat, lanceolate, more attenuated anteriorly, and
with an obtuse caudal apex.

The suctorial pores are relatively larger than in the
D. hepaticum. The anterior globose sucker {a) looks
downwards, and is perforated in the centre by the
mouth; the genital pores are half way between this
and the hinder sucker (^). The transparency of the
integument allows the internal parts to be readily
discerned. The alimentary canal, commencing by a
kind of pharynx, is continued as a very slender tube (c)
to the bursa penis, where it bifurcates, each division
(fZ) being continued without farther ramification along
the right and left sides of the body to the tail, where
it ends in a blind extremity. The minuter excretory
system of vessels has not been discerned in this small Distoma. The
simplicity of its digestive apparatus makes the analogy very close
between the D. lanceolatum and the TcenicB.

In the interspace of the two digestive tubes four opake whitish
spots are visible, of which the three anterior or larger ones (e) form the
testes. Each transmits from its anterior margin a very minute duct,
which, advancing forwards, unite in a common vas deferens, ter-
minating in a small vesicle at the base of the penis, which is pro-

Dist. lanceolatum,
magnified

ENTOZOA. 69

vided with its proper bursa. The ovaria (f,f) are two in number, of
a milk-white colour, situated at the margins of the middle third of the
body, exterior to the alimentary tube. They present a dendritic
form, small branches being given off chiefly from their outer side.
The oviducts run transversely to the middle line, and form there, by
their convolutions, a fourth white opake body behind the testes.
From this subspherical body the common uterine tube (g) is continued.
This is a simple and ample canal, very long and tortuous, occupy-
ing all the posterior part of the interspace of the alimentary forks,
thence con tinned, forwards with decreasing convolutions, and ter-
minating at the vulva.

The digestive system in the species of Diplostomum, a genus which
has two ventral suckers, is as simple as in the Dist. lanceolatum ; but
the blind extremities of the two divisions of the alimentary cavity
are each lodged in a sac, which, from the milky character of its con-
tents, has been termed the chyle receptacle. It is supposed that the
nutritious contents of the alimentary tubes exude through the parietes
of their coecal extremities into these receptacles. Two delicate
vessels are continued from the anterior and outer angle of each
chyle-receptacle, which extend forwards to the anterior third of the
body, and are there brought into communication by a transverse
vessel, which extends across the dorsal aspect of the body. From the
point of union of the transverse with the external lateral vessels, a
single trunk is continued forwards on each side to the anterior angles
of the body, where they bend inwards and unite in the middle line to
form a median trunk, which is continued to the posterior extremity
of the body, distributing or receiving branches on each side through-
out its entire length, and apparently terminating at the posterior
excretory pore. Through the connections of this system of vessels
with the chyle-receptacles, the terminal pore might be regarded as an
anal outlet to the digestive system, and the capillary vessels, ex-
tending from the chyle-receptacles to that pore, as a ramified form of
intestine, fulfilling at the same time the ofliice of lacteals, lymphatics,
arteries, and veins.

Dr. Nordmann, who has contributed to Comparative Anatomy
many excellent illustrations of the vascular system of the Trematoda.,
was the discoverer of the most extraordinary form in the present
class of animals, represented by the species which he has called
Diplozoon paradoxum. This animal consists, in fact, of two bodies
precisely resembling each other, and united, like the Siamese youths,
by a narrow communicating band, through w^hich, however, the
digestive system of one body freely communicates with that of the
other. This digestive system presents the dendritic type of the

60 LECTURE V.

Distoma hepaticum. Each half of the body has its own organs of
circulation, or secretion, and of generation. But for the anatomical
details of the Diplozoon, I must refer to Dr. Nordmann's elaborate
work. This truly paradoxical species^ which is about two or three
lines in length, may be found attached to the gills of the bream.

The genus Planaria, a fresh-water vermiform animal, and not an
internal parasite, is nevertheless referable, by its organisation, to the
order Trematoda. In the Planaria lactea the mouth is situated
upon a proboscis extending from the middle of the inferior surface of
the body. The alimentary canal almost immediately divides into
three principal branches, each of which is again subdivided into a
number of ramified cceca. The two posterior dendritic divisions are
obviously analogous to those in the Distoma hepaticum ; the anterior
division is azygos, and passes along the middle line to the anterior
extremity of the body. The generative organs of the Planariae are
androgynous, and are essentially the same as in the Distomata. The
ova of some species are attached by short filaments to the stems of
aquatic plants. The Planarice also propagate by spontaneous fission,
and are remarkable for the facility with which detached or mutilated
parts assume the form and functions of the perfect animal.

The young of those species of the parasitic Trematoda, whose
development has been most satisfactorily observed, pass the first
period of their existence, like the PlanaricB, as free denizens of the
watery element. The Distomata tereticollis and cylindraceum are
however viviparous. The D. hepaticum and lanceolatum are ovi-
parous. The egg-covering in these and many other species of Trema-
toda is provided with an operculum or lid. The young of the Dist.
hepaticum are spherical and ciliated like the polygastric infusoria ; and
they are provided at this active stage of their existence with a dark
coloured eye speck, and sometimes with a pair of ocelli. The young
of the Dist. glohiporum are of an ash-grey colour, and without an
ocellus. All Trematoda appear first to present the ciliated infusorial
state before they attain their appointed place of abode, where they
undergo their final metamorphosis and develop their generative
organs. There can be little doubt that the sheep, which become in-
fested by the liver-fluke, swallow the ova or embryos that are ejected
upon the pastures or in the drinking places ; and the young flukes
must instinctively pass from the duodenum up the ductus choledochus
to the gall-bladder. Change of pasture, removal to uninfected
grounds, are, therefore, the first steps in the cure and prevention of
the rot-distemper caused by the Distoma, hepaticum.

Of the order Acanthocephala, which includes the most noxious of
the internal parasites, fortunately no species is known to infest the

ENTOZOA. 61

human body. They resemble the Nematoid Entozoa in outward
form, and in the distinction of the sexes, but in their digestive system
they still manifest the sterelminthic type.

The species of this order constitute but one genus, Echinorhynchus,
characterised by a more or less elongated, round, subelastic body, the
head having a retractile proboscis armed with recurved spines. The
Echinorhynchi abound in the lower animals, and are, some cylindrical,
and others sacciform. The largest known species {EchinorJiynchus
gigas) infests the intestines of the hog. As regards the tegumentary and
muscular system, it resembles the Nematoid worms, as well as in its
dioeceous generation; but its digestive system is very different, and some-
what obscurely developed. The mouth is a minute pore, situated on the
extremity of the uncinated proboscis : it leads to two long cylindrical
canals, which adhere to the muscular tunic, and are continued to the
posterior extremity of the body, where they terminate in blind ends ;
and two shorter cylindrical coeca are continued backwards from near
the mouth, and are freely suspended in the anterior part of the
generative cavity : they are called lemnisci. The male organs
consist of two fusiform testes, two vasa deferentia, which unite
together to terminate in a single vesicula seminalis, and a long
intromittent organ provided with a bursa occupying the posterior
extremity of the body, and having a special muscular apparatus for
the retraction and extrusion of the contained organ. The male echi-
norhyncus is generally half the size of the female. The generative
organs in this sex consist of two ovaries and one oviduct. The ovaries
are long and wide cylindrical canals, which of themselves occupy
almost the whole cavity of the body, extending from the proboscis to
the tail, and the common slender oviduct terminates at that extremity
by a very minute pore. The best details of the anatomy of this order
are given by Dr. Westrum* and by Dr. Cloquet, in his prize Essay on
the Anatomy of the Intestinal Worms, f

LECTURE VL

ENTOZOA.

The four orders of the class Entozoa which have already been
described, are less natural than the order Nematoidea, which will

* De Helminthlbus Acanthocephalis, fol. 1821,
t Anatomie des Vers Intestinaux. 4to. 1824.

62 T.ECTURE VI.

chiefly occup)^ our attention in the present lecture. The Cystica^
Cestoidea, Trematoda, and Acanthocephala are far from being
respectively equivalent to the order Nematoidea, either as regards
grade, difference, or circumscription of organic characters. The
transition from the cystic to the taenioid Entozoa is so gradual and
close^ by the Cysticercus fasciolaris, for example, that they are com-
bined in the same order " TcBnioidea^' in the " Regne Animal " of
Cuvier. On the other hand, Cuvier separates the jointless LigulcB, in
which the head has neither suckers, bothria, nor uncinated proboscis,
from the Taenioids, and limits the order Cestoidea to the LigulcB.
It is hardly possible, however, to separate from the Taenioids of
Cuvier, the intestinal Zz^wfe of birds, in which traces of both bothria
and generative organs begin to manifest themselves. With respect
to the higher organised Cestoidea of RudoljDhi, it has been already
observed that they are essentially a composite form of Trematoda,
The extensive and natural grouj) formed by the three androgynous
orders of " Sterelmintha '' form, therefore, the equivalent of the
Nematoidea. The Acanthocephala constitute a more limited, yet
natural order; and the LinguatulcB {Pentastoma of Rudolphi) are
the type of an analogous circumscribed group with a higher type of
organisation, which entitles them to rank in the class Ccelehimitha.
This class includes all the cavitary intestinal worms of Cuvier, with
the exception of the " Vers ridigules " or Epizoa, which are proved
by their metamorphoses to belong to the siphonostomous Crustaceans.
The order Nematoidea, which forms the chief part of the class
Ccelelminthay must chiefly interest the physician, since it includes the
principal internal parasites of the human subject : viz. Trichina
spiralis, Filaria medinensis, Filaria ocidi, Filaria hronchialis, Tri-
chocephcdus dispar, Spiroptera hominis, Strongylus gigas, Ascaris
lumhricoides, and Ascaris or Oxyurus vermicular is • To the order
Nematoidea, repeated examinations, since my first observation of the
minute Trichiiia spiralis*, 'widwce me to refer that singular micro-
scopic parasite. I have satisfied myself of the accuracy of Dr. Farre's
and Dr. Henle's description of the distinct alimentary canal. In a
specimen of Trichina now under the microscope, a loop of the
intestine may be seen protruding through a rupture of the abdominal
wall. The vermicule is always contained in a cyst. The occurrence
of these cysts in vast numbers in the muscular tissue was made
known in a very interesting case published by Mr. Hilton -|- ; and
many others have since been recorded.

* Transactions of the Zoological Society, vol. i. p. S15.
f Medical Gazette, February, 183S.

ENTOZOA. 63

The cysts are very readily detected, by gently compressing a thin
slice of the infected muscle between two pieces of glass and applying
a magnifying power of an inch focus. They are of an elliptical
figure, with the extremities m.ore or less attenuated, often unequally
elongated, and always more opake than the body or intermediate
part of the cyst, which is, in general, sufficiently transparent to show
that it contains a minute coiled-up worm. The usual size of the
cyst is 3^oth of an inch in the long diameter, and ^^Y^yoth of an inch
across their middle part. The cysts are always arranged with their
long axis parallel to the course of the muscular fibres, which probably
results from their yielding to the pressure of the contained worm, and
becoming elongated at the two points where the separation of the
muscular fasciculi most readily takes place, and offers least resistance.

The innermost layer of the cyst can sometimes be detached entire,
like a distinct cyst, from the outer portion, and its contour is gener-
ally well marked when seen by transmitted light. By cutting off
the extremity of the cyst, which may be done with a cataract needle
or fine knife, and gently pressing on the opposite extremity, the
Trichina and the granular secretion with which it is surrounded, will
escape ; and it frequently starts out as soon as the cyst is opened.

When first extracted, the Trichina is usually disposed in two or
two and a half spiral coils ; when straightened out it measures J^th of
an inch in length and -yo o*^ ^^ ^^ ^^^^ ^^ diameter, and now requires
for its satisfactory examination a magnifying power of at least 200
linear admeasurement.

The worm is cylindrical and filiform, terminating obtusely at both
extremities, which are of unequal sizes ; tapering towards one end
for about one-fourth part of its length, but continuing of uniform
diameter from that point to the opposite extremity.

Until lately it was only at the larger extremity that I have been
able to distinguish an indication of an orifice ; and this is situated in
many specimens in the centre of a transverse, bilabiate, linear mouth.

The anterior third of the alimentary canal is more even than the re-
maining part, which presents a sacculated appearance ; in this respect,
the Trichina resembles the newly excluded young of Ascarides and
Strongyli. A small rounded cluster of granules of a darker or more
opake nature than the rest of the body is situated about one-fifth of
the length of the animal from the larger or anterior extremity, and
extends about half-way across the body.

The worm has no organic connection with the cyst: sometimes
two TrichifKB, rarely three, occur in the same cyst.

The Medina or Guinea-worm {Filaria medinensis Gmel.) is de-
veloped in the subcutaneous cellular texture, generally in the lower

64 LECTURE VI.

extremities, especially the feet, sometimes in the scrotum, and also,
but very rarely, beneath the Tunica conjunctiva of the eye. It ap-
pears to be endemic in the tropical regions of Asia and Africa.

The length of this worm varies from six inches to two, eight, or
twelve feet ; its thickness from half to two-thirds of a line ; it is of a
whitish colour in general, but sometimes of a dark brown hue. The
body is round and sub-equal, a little attenuated towards the anterior
extremity. In a recent specimen of small size, we have observed that
the orbicular mouth was surrounded by three slightly raised swellings,
which were continued a little way along the body and gradually lost ;
the body is traversed by two longitudinal lines corresponding to the
intervals of the two well-marked fasciculi of longitudinal muscular
fibres. The caudal extremity of the male is obtuse, and emits a
single spiculum ; in the female it is acute, and suddenly inflected.

The Filaria medinensis, as has just been observed, is occasionally
located in the close vicinity of the organ of vision ; but another much
smaller species of the same genus of Nematoidea, infests the cavity
of the eye-ball itself.

The Filaria oculi humani was detected by Nordmann in the Liquor
morgagni of the capsule of a crystalline lens of a man who had un-
dergone the operation of extraction for cataract under the hands of
the Baron von Grafe. In this instance the capsule of the lens had
been extracted entire, and upon a careful examination half an hour
after extraction there were observed in the fluid above mentioned two
minute and delicate Filarice coiled up in the form of a ring. One of
these worms, when observed microscopically, presented a rupture in
the middle of its body, probably occasioned by the extracting needle,
from which rupture the intestinal canal was protruding; the other
was entire, and measured three-fourths of a line in length ; it presented
a simple mouth without any apparent papillae, such as are observed
to characterise the large Filaria which infests the eye of the horse,
and through the transparent integument could be seen a straight
intestinal canal, surrounded by convolutions of the oviducts, and
terminating at an incurved anal extremity.

The third species of Filaria enumerated among the Entozoa
ho7ni?iis is the Filaria bronchialis ; it was desciribed by Treutler * in
the enlarged bronchial glands of a man : the length of this worm is
about an inch ; it is slender, subattenuated anteriorly, and emitting
the male spiculum from an incurved obtuse anal extremity.

The next human entozoon of the Nematoid order belongs to the
genus Tricocephalus, which, like Filaria, is characterised by an or-

* Opusc. Pathol. Anat. p. 10.

ENTOZOA. G5

bicular mouth, but differs from it in the capillary tenuity of the anterior
part of the body, and in the form of the sheath or preputial covering
of the male spiculum. The species in question, the
Trichocephalus dispar Rud. (^Jig. 29.) is of small size,
and the male is rather less than the female. It occurs

a

Trichocephalus most commonlv in the caecum and colon, more rarely

dispar. Nat. size. '' . ,, . . p

in the small intestmes. Occasionally it is found loose
in the abdominal cavity, having perforated the coats of the intes-
tine. The capillary portion of this species makes about two-thirds
of its entire length ; it is transversely striated, and contains a
straight intestinal canal ; the head («) is acute, with a small simple
terminal mouth. The thick part of the body is spirally convoluted
on the same plane, and exhibits more plainly the dilated intestine ;
it terminates in an obtuse anal extremity, from the inner side of
which project the intromittent spiculum and its sheath.

The species called Spiroptera Homhiis was founded by Rudolphi
on some small nematoid worms expelled, with many larger elongated
bodies of a solid texture, and with granular corpuscles, from the urinary
bladder of a woman, whose case has been described by Mr. Lawrence
in the Medico-chirurgical Transactions.* The Spiroptera varies
from eight to ten lines in length ; the head truncated, mouth or-
bicular, with one or two papillae, body attenuated at both extremities ;
the tail in the female, thicker, and with a short obtuse apex ; that of
the male more slender, and emitting a small tubulus ; a dermal aliform
production near the same extremity determined the worms in question
to belong to the genus Spiroptera.^

The most formidable, but, happily, the rarest of the Nematoid
parasites of man, also infests the urinary system, but is developed in the
kidney, where it has attained the length of three feet, with a diameter
of half an inch ; occasioning supi3uration and destructive absorption
of that important glandular organ.

The male Strongylus gigas {Jig. 30.) is less than the female, and is
slightly attenuated at both extremities. The head («) is obtuse, the
mouth orbicular, and surrounded by six hemispherical papillae ; the
body is slightly marked with circular striae, and with two longitu-
dinal impressions ; the tail is incurved in the male, and terminated
by a dilated pouch or bursay from the base of which the single intro-
mittent spiculum {g) projects. In the female the caudal extremity is
less attenuated and straighter, with the anus a little below the
apex; the vulva is situated at a short distance from the anterior
extremity.

* Vol. ii. p. SS5. f Rudolphi, Synopsis Entozooriim, p, 251.

66

LECTURE VI.

The Strongylus gigas is not confined to the human
subject, but more frequently infests the kidney of the
dog, wolf, otter, racoon, glutton, horse, and ox. It
is generally of a dark blood-colour, which seems to be
owing to the nature of its food, which is derived from
the vessels of the kidney, as, where suppuration has
hi W\] taken place, the worm has been found of a whitish hue.
The round-worm (^Ascaris lumhricoides Linn.)
{Jig. 31.) is perhaps the most anciently known * and
common of the human Entozoa, and is that which has
been subjected to the most repeated, minute, and suc-
cessful anatomical examinations. It is found in the
intestines of man, the hog, and the ox. In the human
subject the round worms are much more common in
children than in adults, and are extremely rare in aged
persons. They are most obnoxious to individuals of
the lymphatic temperament, and such as use gross and
indigestible food, or who inhabit low and damp loca-
lities. They generally occur in the small intestines.

The body is round, elastic, with a smooth shining
surface, of a whitish or yellowish colour ; attenuated
towards both extremities, but chiefly towards the an-
terior one {fig- 31, «), which commences abruptly by
three tubercles, which surround the mouth, and cha-
racterise the genus. The posterior extremity {d)
terminates in an obtuse end, at the apex of which a
small black point may frequently be observed. In the
female this extremity is straighter and thicker than in
the male, in which it is terminated more acutely and
abruptly and is curved towards the ventral side of the
body. The anus is situated in both sexes close to the
extremity of the tail, in form like a transverse fissure.
In the female the body generally presents a constriction
at the junction of the anterior with the middle third,
in which the vulva (e) is situated.

The body of the Ascaris lumhricoides is transversely
^*'^*Naf "ize!^^^" furrowcd with numerous very fine striae, and is marked
v/ith four longitudinal equidistant lines extending from
the head to the tail. These lines are independent of the exterior
envelope, which simply covers them ; two are lateral, and are larger
than the others, which are dorsal and ventral. The lateral lines

* It is the eAfiivs arpoyyvAoi of Hippocrates.

ENTOZOA. 67

commence on eacli side of the mouth, but, from their extreme
fineness, can with difficulty be perceived ; they slightly enlarge as
they pass downwards to about one-third of a line in diameter in
large specimens, and then gradually diminish to the sides of the caudal
extremity. They are occasionally of a red colour, and denote the
situation of the principal vessels of the body. The dorsal and ab-
dominal longitudinal lines are less marked than the preceding,
and by no means widen in the same proportion at the middle of
the body. They correspond to the two nervous chords, hereafter
to be described.

The last species of human Entozoon which remains to be noticed
is the Ascaris vermicularis (Jig. 32.), a small worm, also noticed by
Hippocrates under the name of acncaptg, and claiming the attention of
all physicians since his time, as one of the most troublesome parasites
of children, and occasionally of adults ; in both of whom it infests
the larger intestines, especially the rectum. The size of the male
Ascaris vermicularis is two or three lines, that of the female is five
lines.

The integument in the Nematoid parasites of the human subject, and
in almost all the order, is smooth ; it consists of a thin compact epidermis,
and a cellular corium firmly attached to the outer transverse mus-
cular fibres. The epiderm is developed in the Strongylus horridus
of the water hen, into four longitudinal rows of reflected hooklets ;
and similar spines are arranged in circular groups upon the anterior
part of the Gnathostoma spinigerum.

M. Cloquet, in his elaborate monograph on the Ascaris lumhri-
coides, correctly states that the exterior layers of muscular fibres are
transverse, and the internal longitudinal. In this large specimen of
the Strongylus gigas, which I have dissected for the muscular sys-
tem, you will perceive that a very thin layer of transverse fibres ad-
heres strongly to the integument, the fibres being imbedded in
delicate furrows on the internal surface of the skin ; within this
layer, and adhering to it, but less firmly than the transverse fibres do
to the integument, there is a thick layer of longitudinal fasciculi,
which are a little separated from one another, and distributed not in
eight distinct series, but pretty equally over the whole internal cir-
cumference of the body. Each fasciculus is seen under a high
magnifying power to be composed of many very fine fibres ; but these
do not present the transverse striae which are visible by the same
power in the voluntary muscular fibres of the higher animals. The
inner surface of the stratum of longitudinal fibres is covered with a
soft tissue composed of small obtuse processes, filled with a pulpy
substance, and containing innumerable pellucid globules.

F 2

68 LECTURE VI.

Coincident with this higher development of the muscular sj'stem in
the coelelminthic Entozoa is the more obvious elimination of the nervous
filaments, which in the Linguatula radiate from a distinct suboeso-
phageal ganglion. Amongst the Nematoidea the great Strongylus is
a favourable subject for the demonstration of the nervous system.

In the Strongylus gigas, a slender nervous ring surrounds the
beginning of the gullet^, and a single chord is continued from its
inferior part, and extends in a straight line along the middle of the
ventral aspect to the opposite extremity of the body, where a slight
swelling is formed immediately anterior to the anus, which is sur-
rounded by a loop analogous to that with which the nervous chord
commenced. The abdominal nerve is situated internal to the longi-
tudinal muscular fibres, and is easily distinguishable from them with
the naked eye by its whiter colour^ and the slender branches M'hich it
sends off on each side. These transverse twigs are given off at
pretty regular intervals of about half a line, and may be traced round
to nearly the opposite side of the body. The entire nervous chord
in the female of this species passes to the left side of the vulva, and
does not divide to give passage to the termination of the vagina, as
Cloquet describes the corresponding ventral chord to do in the
Ascaris hmibricoides. In the latter species, and most other Nema-
toidea, a dorsal nervous chord is continued from the oesophageal
ring down the middle line of that aspect of the body corresponding
to the ventral chord on the opposite aspect.

In the Linguatula tcenioides a proportionally large ganglion is
situated immediately behind the mouth, and below the oesophagus :
small nerves radiate from this centre to supply the muscular apparatus
of the mouth and contiguous prehensile booklets ; and two large
chords pass backwards and extend along the sides of the abdominal
aspect of the body to near the posterior extremity, where they ex-
pand and are lost in the muscular tissue. I have already alluded to
the evidences of the nervous system afforded by the ocelli in the
young of some species of Trematoda, in the full-grown Polystoma of
the urinary bladder of the toad and frog, and in the PlanaricB, We
have as yet no evidence that any species of Ccelelmintha possesses
rudimental organs of vision, at any stage of existence.

The digestive organs are very simple, and are subject to little
variety in the Nematoid worms ; an ample alimentary canal, sus-
pended to the parieties of an abdominal cavity, extends in nearly a
straight line from the mouth to the anus, which are at opposite ex-
tremities of the body.

In the Filaria the mouth is a simple circular pore, sometimes
surrounded by a circle of radiated papillae ; a short and slender

ENTOZOA.

69

^ft

oesophagus suddenly dilates into the stomach, which is fusiform, and
indicates the beginning of the intestine by its posterior contraction.

The mouth of the Trichocephalus dispar is small and orbicular ;
the oesophagus is narrow and short ; the intestinal tube is narrow
and sacculated, where it occupies the filiform division of the body,
dilated and simple in the thicker division of the body, at the pos-
terior extremity of which it terminates in a contracted straight tube,
which may be called the rectum : the anus is transverse and bi-labiate.
In the Strongylus gigas the mouth is surrounded by six papillae.
The oesophagus {b,Jig. 30.) is round and slightly contorted, and sud-
denly dilates at the distance of about an inch from the mouth into
the intestinal canal (c) ; there is no gastric portion marked off in
this canal by an inferior constriction, but it is continued of uniform
structure, slightly enlarging in diameter to the anus (d). The chief
31 peculiarity of the intestine in this species is that it is a

four-sided and not a cylindrical tube, and the mesenteric
processes pass from the four longitudinal and nearly equi-
distant angles of the intestine to the abdominal parietes.
These processes, when viewed by a high magnifying
power, are partly composed of fibres, and partly of strings
of clear globules, which appear like moniliform vessels
turning around the fibres. The whole inner surface of
the abdominal cavity is beset with soft, short, obtuse,
pulpy processes, which probably imbibe the nutriment
exuded from the intestine into the general cavity of the
body and carry it to the four longitudinal vessels, which
traverse at equal distances the muscular parietes. The
analogous processes are more highly developed in the
Ascaris lumbricoides, in which species I shall describe the
digestive and nutritive apparatus more in detail.

The mouth {fig. 31, «) is surrounded by three tubercles,
of which one is superior, the others inferior ; they are
rounded externally, triangular within, and slightly granu-
lated on the opposed surfaces, which form the boundaries
of the oral aperture. The longitudinal muscles of the
body are attached to these tubercles ; the dorsal fasciculus
converges to a point to be inserted into the superior one ;
the ventral fasciculus contracts, and then divides, to be
inserted into the two which are situated below. By
Ascaris himbri- meaus of thcsc attachments the longitudinal muscles serve

coidcs.

Half nat. size, to producc the divarication of the tubercles and the open-
ing of the mouth : the tubercles are approximated by the action of a
sphincter muscle.

F 3

70 LECTURE VI.

The oesophagus {fig' 31, ^) is muscular, and four or five lines in
length, narrow, slightly tlilated posteriorly, and attached to the mus-
cular parietes by radiated filaments. Its cavity is occupied by three
longitudinal ridges, which meet in the centre of the canal. It is
separated by a well-marked constriction from the second part of the
alimentary tube (c, c), which extends to the terminal outlet (d), without
presenting any natural division into stomach and intestine. The lower
third of the tube is the widest. Numerous long pyriform villi project
from the mucous lining of the alimentary canal. Many minute filaments
pass from the intestine to the soft obtuse papillae which project from the
walls of the abdomen into that cavity, and which are called " the nutri-
tious appendages" by Cloquet. The nutriment which these processes
or appendages are presumed to imbibe, is collected, according to the
same author, into two canals, situated each in a narrow tract of
opaque substance, which extends along the sides of the body, and
has sometimes been mistaken for a nerve, and which Vallisnieri
believed to be a trachea. Morren has lately described and figured
the nutritive appendages as hollow vesicles : he calls them " Vesicules
aeriennes" because, he says, " they evidently subserve respiration by
furnishing air to the blood." Few physiologists are likely to acquiesce
in this view, which makes the respiratory apparatus of an animal
having no other atmosphere than the mephitic gases of the intestinal
tube, the largest and most extensively developed organ in the whole
body.

With reference to the organisation of the Nematoid Entozoa, not
parasites of the human subject, I shall limit my remarks to those
structures which offer interesting approximations and analogies to the
organisation of higher vermiform animals, and of the existence of
which we must have remained ignorant if our attention had been
wholly confined to the human Entozoa. I may first refer to a
secreting apparatus, consisting of four slender blind tubes, each about
two lines in length, which are placed at equal distances around the
commencement of the alimentary canal in the Gnailiostoma spinigerurHy
a small nematoid worm closely allied to Strongylus, which I dis-
covered in the tunics of the stomach of a tiger.* The mouth of this
Entozoon is a vertical fissure, bounded on each side by a jaw-like lip,
the anterior margin of which is produced in the form of three straight
horny points. The secerning tubes terminate at the mouth by their
smaller extremities, and there pour out a semi-pellucid secretion.
They are analogous to the similarly simple salivary caeca in the
Holoihuria ; and their coexistence with a structure of the mouth,

* Proceedings of the Zoological Society, November, 1836.

ENTOZOA. 71

better adapted tor trituration than any that seems hitherto to have
been detected in the Entozoa, is conformable with the laws which
regulate the coexistence of the salivary apparatus in higher animals.
Cloquet supposes that the thickened glandular parietes of the oeso-
phagus in the Ascaris lumhricoides may provide a secretion analogous
to that of salivary organs. Diesing * has described secerning caecal
tubes analogous to those in Gnatliostoma in species of his genus
Cheir acanthus i in M'hich he, likewise, considers them to be salivary
organs. Mehlis has also described, in the Strongylus hypostomus,
two white organs with blind extremities, which are extended into the
abdominal cavity on each side the intestine, and which appeared to
him to terminate in the animal's mouth. These glands Mehlis sup-
posed to pour out an irritating liquor, which excited an increase
of the secretion of the mucous membrane, to which the parasite
was attached. Dr. Bagge f has more recently described and figured
a pair of blind secerning tubes in the Strongylus auricularis and
in the Ascaris acuminata.^ which unite and terminate by a common
transverse fissure on the exterior of the animal, at a short distance
behind the mouth, and to which he assigns the same irritating office
as that attributed by Mehlis to the glands in the Strongylus hy-
postomus.

The alimentary tube in a species of Ascaris infesting the stomach
of the Dugong is complicated by a single elongated caecum, arising
at a distance of half an inch from the mouth, and continued upward,
so that its blind extremity is close to the mouth. From the position
where the secretion of this caecum enters the alimentary canal, it may
be regarded as a primitive rudiment of the liver.

The generative organs of the Ccelelmintha are more simple than in
androgynous Sterelmintha, or even than in the dicecious Echino-
rhynchi ; yet they are adapted for the production of a surprising
number of fertile ova. In the Linguatula the organs of both sexes,
and especially of the female, are more complex than in the Nema-
toidea : I shall, however, briefly notice them before proceeding to
demonstrate the parts of generation in the human parasites.

The male Linguatula, as in other dicecious Entozoa, is much
smaller than the female : the generative apparatus consists of two
winding seminal tubes or testes, and a single vas deferens, which
carries the semen from the testes by a very narrow tube, and after-
wards grows wider. It communicates anteriorly with two capillary
processes, or peiies, which are connected together at their origin by a

* Annalen des Wiener Museums, Bd. ii. 1839.

f De Evolutione Strongyli auricularis, &e. 4to. 1841, p. 13.

F 4<

72 LECTURE VI.

cordiform glandular body, representing a prostate or vesieula seminalis.
The external orifices of the male apparatus, according to Miram^
are two in number, and are situated on the dorsal aspect of the body
just behind the head. Diesing, however, describes the male Pentas-
toma as having only a single penis, which protrudes just behind or
below the oral aperture.

The female generative organs of the Linguatula tcenioides present
a structure in some respects analogous to that of the Distoma
perlatum : the ovary is a part distinct from the tubular oviduct, and
is attached to the integument or parietes of the body, extending
down the middle of the dorsal aspect. It consists of a thin stratum
of minute granules, clustered in a ramified form to minute white
tubes, which converge and ultimately unite to form two oviducts.
These tubes proceed from the anterior extremity of the ovary, diverge,
pass on each side of the alimentary canal, and unite beneath the
origins of the nerves of the body, so as to surround the oesophagus
and these nerves as in a loop. The single tube formed by the union
of the two oviducts above described, descends, winding round the
alimentary canal in numerous coils, and terminates at the anal
extremity of the body. The single oviduct, besides receiving the
ova from the two tubes, communicates at its commencement with two
elongated pyriform sacs, which prepare and pour into the oviduct an
opaque w^hite secretion.

The male organs in the Nematoidea consist of a single and simple,
slender, elongated tube {Jig. 30, e, e, f) or testis, under its most ele-
mentary form, a seminal reservoir, and an intromittent organ, con-
sisting of a single or double spiculum and its prepuce, or bursa.

The spiculum is simple in the genus Filaria. According to the
observations of Dr. Leblond, the male-duct in the Filaria papulosa
terminates at the anterior extremity of the body, close to the mouth.
From this aperture the slender duct, after a slight contortion, is
continued straight down the body to a dilated elongated sac, which
represents the testis.

In the Trichocephalus dispar the testis, a single tortuous tubule,
commences by a blind extremity near the rectum, passes forwards to
a dilated seminal receptacle at the anterior part of the thick portion
of the body, from which it bends backwards nearly the whole length
of the thick part, constricted at irregular intervals, and terminating
in a narrow straight canal, which is continued into the inverted
pyramidal appendage, or bursa, attached to the hinder extremity of
the bod)^, from which the single spiculum projects.

In the Stro7igylus gigas, the bursa or sheath of the penis, terminates
the posterior extremity of the body, and is a cutaneous production of

EXTOZOA. 73

a round, enlarged, truncated form, with the spiculum projecting from
its centre, as at jig. 30. In other species of Strongylus, as in the
Strong, inflexiis, the bursa penis is bifid, and the intromittent organ
is double. In the Strongylus armatus the bursa is quadrifid. The
SpiroptercE are distinguished by the aliform membranous caudal
appendage in the male.

In the Ascaris lumbricoides the penis projects from the anterior
part of the anus in the form of a slender, conical, slightly curved
process, at the extremity of which a minute pore may be observed
with the aid of the microscope. The base of the penis communicates
with a seminal reservoir, and is attached to several muscular fibres,
destined for its retraction and protrusion : the reservoir is about an
inch in lengthy and gradually enlarges as it advances forwards : the
testis or seminal tube extends to the anterior third of the body,
forming numerous convolutions or loops about the intestine : its
attenuated csecal extremity adheres closely to the dorsal wall of the
abdomen. The total length of the seminal tube is about three feet.
The essential part of the fluid consists of nucleated cells, which, in
the Ascaris lumbricoides, present an irregular, triangular, sub-com-
pressed form. In the Strongylus they are subspherical, with a clear
nucleus ; but undergo, according to Dr. Bagge *, a marked change of
form when introduced into water ; they then become elongated, and
assume a wedge-shape.

From the examples which have been adduced of different genera
of the Nematoidea, we may perceive that although there are many
varieties of structure in the copulative part of the male generative
apparatus, the essential or secerning portion uniformly consists of a
single tube. A like uniformity of structure does not obtain in the
essential parts of the female organs : in a few instances the ovary
is single, corresponding to the testis in the male, but in the greater
number of the nematoid worms it consists of two filamentary tubes.

The Strongylus gigcis is an example of the more simple structure
above alluded to. The single ovary commences by an obtuse blind
extremity close to the anal extremity of the body, and is firmly
attached to the termination of the intestine; it passes first in a
straight line towards the anterior extremity of the body, and, when
arrived to within a short distance from the vulva, is again attached
to the parietes of the body, and makes a sudden turn backwards ; it
then forms two long loops about the middle of the body, and returns
again forwards, suddenly dilating into an uterus, which is three inches,
in length, and from the anterior extremity of which a slender cylin-

* Loc. cit. p. 12,

74 LECTURE VI.

drical tube or vagina, about an inch in length, is continued, which,
after forming a small convolution, terminates in the vulva, at the dis-
tance of two inches from the anterior extremity of the body. In
the Trichocephalus dispar the ovarium and uterus are continuations of
one and the same single tube, which by its folds more or less conceals
the intestines ; the vulva is situated nearly at the junction of the
filamentous with the thick part of the body.

The theory which had suggested itself to Rudolphi of the correla-
tion of a simple oviduct in the female with the spiculum simplex of
the male, and of the double oviduct with a spiculum duplex, is dis-
proved by the circumstance of the uteri and oviducts being double in
the Strongylus armatus and in the Ascaris lumhricoides. In the
Strongylus injiexus, which infests the bronchial tubes and pulmonary
vessels of the porpesse, each of the two female tubular organs may be
divided into ovary, oviduct, and uterus ; the ovary is one inch in
length, commences by a point opposite the middle of the body, and,
after slightly enlarging, abruptly contracts into a capillary duct about
two lines in length, which may be termed the oviduct or Fallopian tube,
and this opens into a dilated moniliform uterus three inches in length.
Both tubes are remarkably short, presenting none of the convolutions
characteristic of the oviducts of Ascaris and Filarial but extend in a
straight line (with the exception of the short-twisted capillary com-
munication between the ovaria and uteri) to the vulva, which
forms a slight projection below the curved anal extremity of the
body.

The reason of this situation of the vulva, seems to be the fixed
condition of the head of this species of Strongylus* In both sexes it
is commonly imbedded so tightly in a condensed portion of the
periphery of the lung, as to be with difficulty extracted ; the anal ex-
tremity, on the contrary, hangs freely in the larger branches of the
bronchi, where the coitus, in consequence of the above disposition of
the female organs, may readily take place.

In the Strongylus armatus the two oviducts terminate in a single
dilated uterus, and the vulva is situated at the anterior extremity of
the body, close to the mouth.

I find a similar situation of the vulva in a species of Filaria, about
thirty inches in length, which infests the abdominal cavity of the Rheat
or American ostrich. The single portion of the genital tube con-
tinued from the vulva, is one inch and a quarter in length ; it then
divides, and the two oviducts, after forming several interlaced con-
volutions in the middle third of the body, separate ; one extends to
the anal, the other to the oral extremities of the body, where the
capillary portions of the oviducts respectively commence.

ENTOZOA.

75

In tlie Ascaris vertnicularis, the vulva {fy' 32, e) is situated aljout
one fourth of the length of the body from the head.

In the Ascaris lumhricoides the female organs
{fig. 31.) consist of a vulva, a vagina, and a
uterus, which divides into two long tortuous
oviducts, gradually diminishing to capillary
^^\.0\ tubes, which may be regarded as the ovaria. All

these parts are remarkable in the recent animal
for their extreme whiteness. The vulva is situ-
ated on the ventral surface of the body, at the
junction of the anterior and middle thirds of the
body, which is generally marked at that part by
a slight constriction. The vagina is a slightly
wavy canal five or six lines in length, which
passes beneath the intestine and dilates into
the uterus. The division of this part soon takes
place, and the cornua extend with an irregularly
wavy course to near the posterior extremity of
the body, gradually diminishing in size; they
are then reflected forwards, and form numerous,
and apparently inextricable, coils about the two
posterior thirds of the intestine.

In the Nematoidea the male individual is al-
ways smaller, and sometimes disproportionately
so, than the female. At the season of reproduc-
tion the anal extremity of the male is attached
to the vulva of the female, by the intromission
of the single or double spiculum, and the ad-
hesion of the surrounding tumid labia ; and, as
the vulva of the female is generally situated at a
distance from either extremity of her body, the
male has the appearance of a branch or young
individual sent off by gemmation, but attached
at an acute angle to the body of the female.*

The evidence of the fertility of the compound
cestoid Entozoa, was sufficiently marvellous :

Ascaris vermicuiaris. that which I havc now to adduce, from a calcu-
lation made by Dr. Eschricht, in reference to the
Ascaris lumhricoides, the commonest intestinal parasite of the human

* See Figures of such Nematoid Entozoa in Bremser, Icones Helminthum,
tab. iii. fig. 8. 15. ; and Gurh, Lehrbuch der Patholog., Anatomie der Haus-
Saiigethiere, tab. vi. fig. 35.

76 LECTURE VI.

species, is scarcely less surprising. The ova are arranged in the
ovarian and uterine tubes like the flowers of the plantago, around a
central stem or rachis. There are fifty in each circle, that is to say,
you might count fifty ova in every transverse section of the tube.
Now the thickness of each ovum is 3^^^ of a line, so that in the length
of one line there are 500 wreaths of 50 eggs each, or 25,000 eggs !
The length of each division or horn of the uterus is 16 feet or 2304
lines, which for the two horns gives a length of 4608 lines. The
eggs, however, gradually increase in size so as to attain the thickness
of -^Q of a line : we, therefore, have at the lower end of the horn 60
wreaths of ova, or 3000 ova in the extent of one line. The average
number through the whole of the extraordinary extent of the tube
may be taken at 14,000 ova in each line, which gives sixty-four
7nillions of ova in the mature female Ascaris lumbricoides !

The embryo is not developed within the body in this species ; the
ova may be discharged by millions, and most of them must, in large
cities, be carried into streams of water. An extremely small pro-
portion is ever likely to be again introduced into the alimentary
canal of that species of animal which can afford it an appropriate
habitat. The remainder of the germs doubtless serve as food to nu-
merous minute inhabitants of the water ; and the prolific Entozoa may
thus serve these little creatures in the same relation, as the fruitful
Cerealia in the vegetable kingdom stand to higher animals, and
minister less to the perpetuation of their own species than to the
sustenance of man.

The oviparous Entozoa present, perhaps, the most favourable
subjects for studying with the requisite attention the successive steps
of that process by which the germinal vesicle and yolk become finally
transmuted into the young and active worm.

I described and showed diagrams of some of these changes in the
ova of the Strongylus inflexus in my Lectures on Generation in 1 840.
Mr. Quekett* has since added other observations on the develop-
ment of the same species of Entozoon ; but the most accurate and
complete illustrations of the process had previously been published
by Professor Siebold f and Dr. Bagge:j:, from observations made
upon the ova of the Strongylus auricularis and the Ascaris acuminata,
both of them viviparous species of Nematoidea» Dr. Bagge finds at
the delicate blind extremities of the ovaria the germinal vesicles, which
are at first few and scattered, but become more closely aggregated as
they descend along the tube ; whilst the ovum is progressively

* Trans, of the INIicroscop. Society, vol. i. p. 44.
f Burdach. Physiologie, vol. ii. p. 208.
X De Evolutione Strongyli, &c. 4to. 1841

ENTOZOA.

77

enlarged, b}^ the multiplication of the opake granules of the yolk
around the essential vesicle : then the delicate, smooth, and polished
membrana vitelli is acquired. Towards the fundus. Dr. Bagge
describes the germinal vesicle as being obscured by the aggregation
of the vitelline granules around it; and he thinks it probable that the
vesicle bursts and pours its contents over those granules. At all
events it ceases to be visible as a clear central cell.* The ovum is
now apparently occupied by the opake and minute vitelline granules,
which become aggregated or condensed, so as to leave a clear narrow
interspace between the vitelline mass and the smooth outer membrane
{^jig. 34.). In the centre of this mass, however. Dr. Bagge detects

a clear cell (33), but much more minute than the primitive ger-
minal vesicle. This clear cell becomes lengthened, and its rounded
extremities mutually recede ; while the middle part becomes at-
tenuated (yfig- 35.), and finally breaks ; whereby two pellucid cells are
developed, which recede towards the opposite poles of the ^^^
{fig> 36.) ; and this process immediately precedes the first division of
the yolk into two parts {^fig. 37-), each of which has the pellucid cell
for its centre. This preliminary division of the clear central cell to the
spontaneous fission of the yolk is closely analogous to that division of
the central cell in the polygastrian animalcule, preparatory to the
spontaneous division of its body into two individuals, which Ehrenberg
has described. Dr. Bagge next traces the changes of the pellucid
central cell of each primary division of the yolk, and describes it as
undergoing the same change of form and division {fig. 38.) which he
had observed in the primitive cell : and these changes are followed
by the spontaneous fission of each primary division of the yolk,
whereby the quadripartite character of the ovum is produced {Jig.^9.)y

* Dr. M. Barry's description of the true processes which, at this stage, obscure
the germinal vesicle will be found in the Philos. Transactions, 1839, p. 307.

78 LECTURE VI.

analogous to that stage in the generation of the Chlamydomonas^
which is represented at page 24. Jig, 14.

There is a close and interesting analogy between the above phe-
nomena, which were published in 1841, and some of those communi-
cated by Dr. M. Barry, to the Royal Society, in January 1841, and
published in the Philosophical Transactions of the same year. The
clear central nucleus of the blood corpuscle is there shown to form
two discs *, which give origin to two cells. We may, likewise, discern
in the pellucid nucleus of the yolk, dividing and giving origin to two
yolk-cells, according to the German author, the hyaline nucleus of
Dr. M. Barry, w^hose important properties and changes have been
so ably elucidated and generalised by that accomplished and patient
observer.

Dr. Bagge traces and illustrates the subsequent divisions of the yolk
in the ova of the Entozoa, through the four, eight (^y. 40.), and
sixteen fold divisions, until the number of yolklets {fig. 41.), like
those of the young of the Paramecium in Ehrenberg's experiment,
becomes incalculable. A division of the hyaline nucleus has doubt-
less preceded the formation of each of these divisions ; and the sub-
divided yolk granules have clustered themselves around their respective
centres like the working bees around their royal parent. Thus the
subdivisions of the yolk decreasing in size as they augment in number
the vitelline matter is at length, by the reiterated processes of de-
velopment, liquefaction and assimilation of nucleated cells, sufficiently
subdivided and refined, and each subdivision or cell, by the con-
comitant partition of the hyaline, has become adequately vitalised,
to be capable of its further metamorphosis into the appropriate tissue
of the embryo worm.

The minutely subdivided mass is now observed to present a
lateral indentation ; and, as this deepens, it assumes the form of
a short thick cylinder, bent upon itself {fig. 42.). By the length-
ening and attenuation of the cylindrical mass, the bend assumes
the character of a coil {fig. 43.) ; and now something like an in-
tegument, containing a fine granular tissue, may be discerned.
Further elongation, attenuation, more complicated coiling, and a
greater clearness of the tissues of the embryo worm make its
character plainly manifest, and the alimentary canal can be dis-
tinguished from the integument, both having been formed, by the
subdivision and metamorphosis of the primitive cells {fig. 44.). The
young animal thus built up, now begins to move briskly within the

* See Philos. Trans. 1841. PI. xviii. fig. 37.

ENTOZOA. 79

egg-membrane^ assimilates the remaining vitelline mass, and is soon
strong enough to burst its prison, and commence its independent
career of existence.

The Entozoa are hardly less remarkable for their tenacity of life
and revival from a state of apparent death than the Infusoria, and
the knowledge of this property is indispensable to a fair estima-
tion of the chances of the re-introduction of the ova of Entozoa
into the bodies of living animals. In no class of animals has the
origin from equivocal generation been more strenuously contended
for than in regard to the Entozoa. The great entozoologists
Rudolphi and Bremser were advocates of this doctrine; and Bremser
did not scruple to charge the Berlin professor with a physiological
heresy, when he ventured to account for the high organisation of
certain Ligulse infesting piscivorous birds, by the hypothesis that they
had been developed from the lower grade which they previously
exhibited in the cold-blooded fishes swallowed by the birds, through
the stimulus of the heat and nutritious secretions of the more com-
fortable intestinal domicile to which they had thus been accidentally
introduced.

The advocates for the equivocal generation of the Entozoa adduce
the fact that herbivorous mammals are not less subject to Entozoa
than carnivorous ones : and how, they enquire, could the ova of
Entozoa be preserved in the water that serves as the drink of such
animals ? Or how, having become dried in the air, could such ova
afterwards resume the requisite vitality for embryonic development ?
We may admit that the ova of Entozoa could not, like the much
more minute ova of Pologastria, remain suspended in the atmosphere,
since they are specifically heavier than water ; but, with respect to
their powers of retaining dormant life, we have sufficient analogical
evidence to reject the assumption that they soon fall into decompo-
sition.

Mr. Bauer * has recorded many experiments on the Vibrio tritici^
or parasite of wheat, a minute worm possessing the essential organis-
ation of the Nematoidea, not less remarkable in their results than
those of Spalanzani on the Rotifer : the Vibriones were dried, and
when re-moistened, after the lapse of four to seven years, they re-
sumed their living and active state. Dr. Biainville states that the
Filaria papillosa revives from a similar state of torpidity produced
by desiccation.

It has been proved that the mature Entozoa will resist the effects
of destructive agents, as extremes of heat and cold, to a degree

* Philos. Trans. 1823, p. 1.

80 LECTURE VI.

beyond the }3owers of endurance of the Rotifera, and which woidd be
truly surprising were not the simplicity of the organisation of the
Entozoa taken into account. A Nematoid worm has been seen to
exhibit strong contortions — evident vital motions — after having been
subjected above an hour to the temperature of boiling water, with a
cod-fish which it infested ; and, on the other hand, Rudolphi relates
that the Entozoa of the genus Capsularia, which infest the herrings
that are annually sent to Berlin, hard frozen and packed in ice, do,
when thawed, manifest unequivocal signs of restored vitality. If,
then, the fully developed and mature Entozoa can resist such
powerful extraneous causes of destruction, how much more must the
ova possess the power of enduring such without losing their latent
life.

Burdach, who has summed up the evidence at great length in
favour of the equivocal generation of the Entozoa, adduces the
example of the ovoviparous species as involving the limitation of the
offspring to the lifetime of the individual which they themselves
infest ; but on this point Dr. Eschricht * has well observed that the
transmission of the living young of the Strongylus inflexus from one
porpoise to another is readily explicable. This species of Strongylus
lives in the bronchial tubes, with its head immersed in the substance
of the lungs, and its tail extended into the larger branches of the
trachea. The living young must naturally escape into the mouth,
and, as porpoises are gregarious, the young worms would, by a short
passage through the water, readily be introduced into the mouth of
another porpoise, and so reach the trachea.

The young of most Entozoa are subject to metamorphoses. I
have already alluded to those of the Cestoidea in which the head
in all the species seems first to be provided with six hooks, f
Those of the Trematoda are the most astonishing, and the loco-
motive condition of the young Distoniata evidently relate to the
securing their entry into the animal's body which they are destined
to infest. Dr. Siebold has noticed the difference of form between
the young of the Echinorhynchi and their viviparous parents ; and
this difference was so great in regard to the viviparous Filaria
medinensis, that Dr. Jacobson was led to suppose its multitudinous
progeny to be parasites of the parasite. Dr. Eschricht has observed
that the flesh of fishes in summer is often studded with small worms,
which, in one instance, he ascertained to be Echinorhynchi ; and he
suggests whether it may not be the breeding place of such species,

* Essay on Spontaneous Generation, Edinb. Philos. Journal, vol. xxxi. p. 345.
\ Dujardin, in Annales de Science Nat. 1838.

POLYPI. 81

and whether the Trichina spiralis may not belong to the same
category. But how these embryos (if they be embryos) are diffused
through the intermuscular cellular tissue, can only be known after
long and laborious investigations : and nothing is more true than
that a particular enquiry will be required for each particular species.

LECTURE YII.

POLYPI.

The two great divisions of the sub-kingdom Zoophyta, — viz. the
Infusoria and Entozoa, which have hitherto engaged our attention,
approximate to the vermiform type ; and each ascends by rapid steps
to the confines of the articulate sub-kingdom. The remaining classes
of the Zoophyta are constructed on the radiated type, and some
of them, as the Bryozoa and Acalephce^ conduct to the molluscous
series.

To-day I have to request your patient attention to the history of a
race of animalcules as widely diffused, almost as numerous, and some
of them hardly less minute than the Infusoria^ with which we com-
menced the survey of the vermiform zoophytes. Our present subjects
form at least three classes of radiated zoophytes, which have been
grouped together under the common name of Polypi, on account of
their external resemblance to the many-armed cuttle-fishes, which
were so denominated by the ancient Greek naturalists. But the
knowledge of the organised beings now called Polypi, as members
of the Animal Kingdom, is of comparatively recent introduction :
it cannot be dated further back than the time of Imperato* and
Peyssonel.f Amongst those naturalists who have subsequently con-
tributed to improve and extend the history of the Polypes, our
countryman Ellis will always take a high rank.

A polype generally presents a cylindrical or ov 1 body, with an
aperture at one of its extremities, which is surrounded by a coronet
of long tentacula. In most of the class this aperture leads to a simple
digestive cavity, consisting of a stomach without intestine : in the
higher organised species, the digestive sac is prolonged into an intes-

* Historia Naturale, fol. 1599.

t Traite du Corail, Phil. Trans. 1756; communicated to the French Academy,
1727.

82

LECTUEE VII.

tinal canal, which is bent upon itself, and terminates by a distinct
anus opening upon the external surface. The organisation of the
polypes is in general very simple, and their faculties or vital phe-
nomena seem feeble and inconspicuous. Nevertheless, the influence
of their combined powers in modifying the crust of the earth, i&
neither slight nor of limited extent.

This great division of the radiated animals is divided into three
groups or classes, according to the modifications of the alimentary
canal. In the first and lowest organised class, which I have called
Hydrozoa *, digestion is performed by the secretion of a simple sac,
excavated in the gelatinous and granular parenchyme of the body. In
the second class, called Anthozoa, the digestive sac, which, like the
first, throws out the rejectamenta by the same aperture as that which

receives the nutriment, is
suspended by a series of
vertical folds of mem-
brane in a distinct abdo-
minal cavity, to the outer
parietes of the body. In
the third and highest
class, QdiWed. Bryozoa, the
alimentary canal, which i&
likewise suspended loosely
in an abdominal cavity,
is provided, as has been
already stated, with a dis-
tinct mouth and anus.

It is remarkable that
the most locomotive of
the Polype tribe, is at the
same time the type of the
lowest organised group.
The Hydra, or common
freshwater Polype {fig.
45.), consists, when mag-
nified even with a mode-
rately high power, appa-
rently of a granular sub-
stance of a greenish or
reddish hue, the granules
or cells being loosely connected by a semifluid matter. The external

C\^

Hydra fusca.

* Dunorphcea of Ehrenberg
of Farrc.

Sertulariens of Mihie Edwards ; Nudibrachiota

roLYPi. 83

cells are condensed^ and elongated in the axis of the body, so as to
form two tegunientary layers : the internal cells are elongated trans-
versely to the axis of the body, and form a stratum of villi, projecting
into the abdominal cavity : the thick intermediate mass of nucleated
cells seems to fulfil the ordinary functions of muscular or contractile
tissue.

The hydra commonly adheres by a small prehensile disc or rudi-
mentary foot (^fig. 45. (T)-, situated at tiie extremity of the stem or
body opposite to the mouth. When the little animal would change
its position it slowly bends its body, and, fixing one or more of its
tentacula to the supporting surface, detaches the posterior sucker
approximates it to the head, and advances by a succession of these
leech-like motions. The hydra can make progress in water, as well as
on a solid plane ; when it would sv/im it suspends itself to the surface
of the water by its foot or terminal sucker, which it expands, and ex-
poses to the air : the disc soon dries, and in this state, repelling
the surrounding water, it serves as a float, from which the hydra
hangs with its mouth downwards, and can row itself along by means
of its tentacula. Its ordinary position is one of rest, adhering to
an aquatic plant by its terminal sucker, with the dependent oral
tentacula spread abroad in quest of prey.

Should a small Nais or Entomostracan, or any of the larger
Infusories, come within the reach of the little carnivorous polype, they
are immediately seized, pulled towards the mouth (^fig> 45. ^), and
swallowed. The rapidity of the digestive process is manifested by the
diffusion of any characteristic colour of the animalcules swallowed,
through the gelatinous parenchyma of the devourer ; and when this
process is completed, the indigestible debris of the prey are rejected
by the same aperture which had just gorged it. Although the in-
digestible parts of the food are palpably rejected by the mouth, yet
a careful investigator, Corda*, affirms the existence of an anal outlet
i^fig- 45. c), and figures it of small size, close to the hind sucker or foot.
It may give passage to certain excretions of the villous lining membrane
of the alimentary cavity.

Each tentaculum in the Hydra grisea, acording to this observer,
is a slender membranaceous tube, filled with a fluid albuminous
substance mixed with oil-like particles. This substance swells out
at certain definite places into denser nodules, which are arranged
in a spiral line {Jig. 45. «, a). Each nodule is furnished with
an organ of touch, and another singularly constructed one for
catching the prey. The organ of touch consists of a fine sac,

* Nova Acta Physico Medlca, &c. Bonn, vol. xviii, 1836, tab. xvi.
G 2

84 LECTURE VII.

inclosing another with thicker parietes, and within this there is a
small cavity. From the point where the two sacs coalesce above,
there projects a long spine, which is non-retractile. The seizing
organ consists of an obovate transparent sac, immersed in the
nodule with a small aperture. At the bottom of the sac, and within
it, there is a solid corpuscule, which gives origin to a calcareous
sharp sagitta or spine, that can be pushed out at pleasure, or with-
drawn until its point is brought within the sac. When the hydra
wishes to seize an animal, the sagittse are protruded, by which means
the surface of the tentacula are roughened, and the prey more
easily retained : Corda believes that a poison is at the same time
ejected. The nodules of the tentacula are connected together by
means of four muscular bands, which run up, forming lozenge-shaped
spaces by their intersections : these are joined together by transverse
bands. There is no communication between the tube of the tenta-
culum and the cavity of the body. The lip of the mouth is armed
with spines, similar to those of the tentacula ; but the rest of the body
is destitute of them.

That the tentacula have the power of communicating some be-
numbing shocks to the living animals which constitute the food of the
Hydra, is evident from the effect produced, for example, upon an En-
tomostracan, which may have been touched, but not seized, by one
of these organs. The little active crustacean is arrested in the midst
of its rapid, darting motion, and sinks, apparently lifeless, for some
distance ; then slowly recovers itself, and resumes its ordinary move-
ments. These and other active inhabitants of fresh waters, whose
powers should be equivalent to rend asunder the delicate gelatinous
arms of their low-organised captor, do, nevertheless, perish almost
immediately after they have been seized, and so countenance the
opinion of Corda of the secretion of a poison ; unless, indeed, the
little polype may have the power of communicating an electric shock.

The most extraordinary properties of the Hydra are, however,
those which best accord, and might be expected to be associated,
Mdth its low and simple grade of organisation ; although they excited
the greatest astonishment in the physiological world when first
announced by their discoverer, Trembley, and are often still called
wonderful.

If a polype be transversely bisected, both halves survive ; the
cephalic one developing a terminal sucker, the caudal one shooting
forth a crown of tentacula ; each moiety thus acquiring the characters
of the perfect individual. But in a healthy and well-fed Hydra, the
same phenomena will take place if it be divided into ten pieces. The
Hydra, notwithstanding the want of a nervous centre thus indicated,

POLYPI. 85

and the absence of any hitherto recognised nervous filaments, mani-
fests an obvious predilection for light, and, when confined to a glass,
always moves itself to the brightest side. Trembley succeeded in in-
verting one of these delicate animalcules, and the creature soon ac-
commodated itself to this singular change in its condition : digestion
being effected as actively by the surface which before was external,
as by that which had been the digestive surface ; whilst this as readily
assumed the ordinary gemmiparous function of the skin.

The Hydras are not less remarkable for their power of gene-
ration than for that of regenerating mutilated parts. They have
been observed to multiply by spontaneous fission, dividing them-
selves transversely : but the most ordinary process of generation
is by the development of young polypi, like buds, from the ex-
ternal surface of the old one. It is, however, most probable that
in these cases the gemmation is preceded by the development
and fecundation of the true ovum, beneath the integument. The
Hydra unquestionably presents a periodical development of sexual
organs of two kinds : one, at the anterior or oral extremity of
the body consists of small nodules or sacs, which Ehrenberg dis-
covered to contain moving filaments, or seminal animalcules : another
series of cells, developed in the posterior part of the stem, contain
ova, which, after impregnation, are discharged, but sometimes are
retained, and then grow out like buds. Sometimes one individual
Hydra developes only the male cysts, or sperm-vesicles ; sometimes
only the female ones, or ovisacs ; but the rule is generally to have
both kinds.

The seas which wash our own shores are tenanted by numerous
forms of minute Polypi^ having essentially the same simple organis-
ation as the Hydra ; but which are protected from the dense briny
element surrounding them by an external horny integument. Now
these likewise develope new polypes by gemmation ; but, as the ex-
ternal crust grows with the growth of the soft digestive sac, the
young polype adheres to the body of the parent, and, by successive
gemmations, a compound animal is produced. Yet the pattern
according to which the new polypes and branches of polypes are
developed is fixed and determinate in each species ; and there conse-
quently results a particular form of the whole compound animal or
individual by which the species can be readily recognised. This
hydriform polype-animal, or association of polypes, resembles a
miniature tree ; but consists essentially of a ramified tube of irritable
animal matter, defended by an external, flexible, and frequently
jointed, horny skeleton ; fed by the activity of the tentacula and by
the digestive powers of the alimentary sacs of a hundred polypi, the

G 3

86 LECTURE YII.

common produce of M'liich circulates through the tubular cavities for
the benefit of the whole animal. These currents of the nutrient fluid
have been observed and described by Cavolini, and more recently by
Mr. Josej^h Lister. The genera Sertularia, Campanularia^ Tiibu-
laria, &c., which form the principal subjects of Ellis's beautiful and
classical work on Corallines, compose the present division of the
compound Hydrozoa, or hydriform polypes.

The peculiar external horny defence prevents, as I have just ob-
served, the exercise of the gemmiparous faculty from effecting any other
change than that of adding to the general size, and to the number of
prehensile mouths and digestive sacs, of the individual coralline. It is
equally a bar to propagation by spontaneous fission ; so that the ordinary
phenomena of generation by ova are more conspicuous in the composite
than in the simple Hydrozoa, At certain points of these ramified po-
lypes, which points are constant in, and characteristic of, each species,
there are developed little elegant vase-shaped sacs, which are filled
with ova, and are called the " ovigerous vesicles." These are some-
times appended to the branches, sometimes to the axillae^ of the
ramified coralline : they are at first soft, and have a still softer lining
membrane, which is thicker and more condensed at the bottom of the
vesicle : it is at this part that the ova are developed, and for some
time they are maintained in connection with the vital tissue of the
polype by a kind of umbilical cord. The ova undergo a certain
amount of development in this situation, and acquire a ciliated
surface. By virtue of those primitive and universal organs of motion,
the vibratile cilia, they detach themselves from the umbilical stem, and
eff'ect their escape from the cell. Having rowed to a convenient dis-
tance from the parent, the ciliated bulb subsides into an amorphous de-
pressed mass, which shoots out its tissue in irregular rays upon the sup-
porting body, to form the roots of attachment, and sends ujDwards a
pyramidal process or stem, which, at a little distance, expands into
a hydriform polype. The supporting stem continues to ascend,
divides, and proceeds to develope other polype mouths, according to
the prescribed pattern, and finally the ova and ovigerous sacs. In
some species the ovigerous cell is provided with a distinct lid or
operculum, which defends the ova from the sea-water in their tender
stages of development ; then drops off", and, allowing ingress to the
water, occasions an increased activity in the ciliated gemmules.
Sometimes a small polypus is developed from the mouth of the
ovigerous cell, in which state they have been described by Lowen as
the female polypes, the smaller and ordinary food-catching and
digesting polypes being regarded as the males. In all the compound
Hydrozoa, the ovigerous sacs are deciduous, and, having performed

POLYPI. 87

their functions in relation to the development of the new progeny,
drop off like the seed-capsules of plants. This phenomenon afforded
to the early botanists an additional argument in favour of the relation
of these ramified and rooted animals to the Vegetable Kingdom.
The Anthozoa {Jig. 46.), or polypes of the second great class, cha-
racterised by a distinct abdominal cavity in which their
simple digestive sac is suspended, constitute the most nu-
merous and important part of the whole race, and in-
clude the largest individuals. They are principally the
inhabitants of the warm&r or tropical seas.

They are subdivided according to the number of their
oral tentacula. Most of the species have only eight of
these radiated prehensile organs : the rest have a greater
number. To this latter group belong the soft-bodied
and solitary species called Sea-Anemonies or Actinice,
which are common upon our own coasts.

In the species here dissected, you will see that the skin is thick
and opake : in the living Actinia, it is lubricated by a mucous
secretion : the disposition of the muscular fibres by which it is
acted upon, is indicated by the superficial strise. In the middle
of the circle of the tentacles is situated the mouth, from which a
short oesophagus leads to a large gastric cavity, the parietes of which
are connected by a great number of membranous vertical folds with
the external wall of the body. The tentacula are tubular ; they are
perforated at their free extremity, and communicate with the inter-
spaces of the mesogastric lamellae. They absorb the sea-water into
these spaces, and are elongated by the injection of that water into
their interior. The extended surface of the abdominal cavity is
beset with innumerable minute cilia, through the action of which
it is bathed by a constant current of the admitted medium of re-
spiration, the sea-water.

The ova are formed within the mesogastric folds : beneath the
folds is situated an equal number of sacs or bodies composed
of convoluted tubes which contain granules and spermatozoa, de-
monstrating the androgynous nature of the Actinia. The impreg-
nated ova are developed into ciliated gemmules in the abdominal
reservoir of sea-water : then make their way by the small inferior
aperture of the stomach into that cavity, and escape by the mouth of
the parent.

Many of the large actiniform polypes of the tropical seas com-
bine with a structure which is essentially similar to our own sea-
anemonies, an internal calcareous axis or skeleton, which, pene-
trating the interior of the mesogastric folds, presents the lamel-

G 4

88

LECTURE VII.

lated and radiated structure ^^llicll we recognise in the enduring
support of the large FungicB and in the polype cells of the skeletons
of the Caryophillece, MadreiJorce^ &c.

The species of polypes which take the most important share in the
fabrication of the coral islands and reefs, belong to the present group,
and have esentially the organisation of the sea-anemony, which has
just been described.

To the eight-armed division of the Anthozoic Polypes belong those
species which have an internal ramified calcareous or jointed axis, as
the red coral polype {fg. 46. c), the gorgonia, and the isis. To this
division likewise belongs our common Alcijonium, or dead-man's-
toes, in which the hard axis is wanting ; and the phosphorescent Sea-
pens^ the Veretillum, and other PennatulidcB, in which it is in de-
tached pieces.

These are all examples of compound AntJwzoa, differing from the
compound hydriform polypes in having an internal instead of an
external skeleton. The body of each polype {Jig. 47.) is relatively

longer than in the ActinicB ; the pre-
hensile tentacles (a, a) are broad and
pectinated : at the centre of their base
is situated the mouth (h), which leads
to a straight membranous alimentary
cavity, fixed by vertical septa {d, d)
to the external integument ; which
septa are continued down the general
visceral cavity. The digestive canal
communicates with this cavity by a
small orifice (e) at its inferior part.
Ovaria and tortuous filamentary se-
creting organs {/) analogous to the
testes in the Actinia, are developed
in the common visceral cavity. A
delicate network of vessels conveys
the nutrient fluid to the common con-
necting parenchyma of the entire
compound animal.
This parenchyma is strengthened in our common Alcyonium by
numerous minute calcareous spiculae. Analogous spiculae, but of
varying and characteristic forms, strengthen likewise the animal
crust of the red corals, jointed corals, and Gorgoniae ; but to these is
superadded the internal branched axis, w^hich, according to its com-
position and structure, characterises the difi'erent genera of this group.
In one genus, the external position of the skeleton which characterises
the hydriform compound polypes is repeated, viz. in the Tuhipora

Polype of the red coral.

POLYPI. 89

musica; but the organisation of the polypes, protected by the crim'*on
pipes of this beautiful coral, is essentially the same as in the Alcyonium,
Gorgo7iia, and Pennatula.

The most important productions of the apparently insignificant
race of Polypi are the accumulations of the calcareous skeletons of the
Anthozoci, which form the coral islands and reefs; — the dread of the
navigator, — the admiration of the lover of the picturesque, — the
subjects of the closest and most interesting speculation to the na-
turalist and geologist.

That masses of rock many leagues in extent should be founded in
the depths of the ocean, anv built up to the height of hund^'eds of
feet by minute, frail, gelatinous animalcules, is indeed a phenomenon
calculated to stagger the unversed in zoological science, and M^hich
has demanded the repeated observation of the most accomplished and
enlightened voyagers to render intelligible.

These zoophytic productions have been recently classified by
Mr. Darwin * under three heads : ' atolls,' ' barrier reefs,' and
' fringing reefs.' The term Atoll is the name given to the coral-
islands, or lagoon-islands by their inhabitants in the Indian Ocean.
An atoll consists of a wall or mound of coral rock {^fig. 50. r'\ r^^),
rising in the ocean from a considerable depth, and returning into
itself so as to form a ring, with a lagoon, or sheet of still water
(Jig. 50. 7i) in the interior. The wall is generally breached in
one or more places, and when the breach is deep enough to admit
a ship, the atoll affords it a convenient and safe harbour. The outer
side of the reef usually sinks to a depth of from two to three hundred
fathoms, at an angle of forty-five degrees or more : the internal side
shelves gradually towards the centre of the lagoon, forming a saucer-
shaped cavity, the depth of which varies from one fathom to fifty.
The summit of the exterior margin of the reef or wall is usually
composed of living species of Porites and 3Iillepora. The Porites
form irregularly rounded masses of from four to eight feet broad,
and of nearly equal thickness ; other parts of the reef are composed
of thick vertical plates of the Millepora complanata intersecting each
other at various angles, and forming an exceedingly strong honey-
combed mass. The dead parts of these calcareous skeletons are
often cemented over with a layer of the marine vegetable xalled Nut-
lipora, which can better bear exposure to the air.

This strong barrier is well fitted to receive the first shock of the
heavy waves of the fathomless ocean without; and >vhat at first
appears surprising, instead of wearing away at its outer edge, it is
here only that the solid reef increases. The coral animals thrive

* Structure and Distribution of Coral Reefs, 8vo. 1842.

90 LECTURE VII.

best in the surf occasioned by the breakers. Through this agitation
an ever-changing and aerated body of sea water washes over their
surface, and their imperfect respiration is maintained at the high-
est state of activity. Abundant animalcules, and the like objects
of food, are thus constantly brought within the sphere of the ten-
tacula of the hungry polypes. Their reproductive gemmules are
rapidly and extensively dispersed amongst the crevices of the cal-
careous mass.

By the force of unusual storms this outer reef is occasionally
breached, and huge masses are torn off and driven towards the
lagoon, where they form an inner barrier or reef. The broken
surface becomes the seat of attachment of the young of the neigh-
bouring corals, the successive generations of which, by the rapid
growth and develoj^ment of their calcareous skeleton, soon repair
the damage of the storm. The masses of broken coral thus driven
inward towards the lagoon, accumulate in time to the height of some
feet above high water. These fragments are mixed with sand and
shells, and form a favourable soil for the development and growth
of vegetables, as cocoa palms, the large nuts of which may be
borne hither by currents of the ocean, from Sumatra or Java, 600
miles distant. Turtles likewise float to the nascent island, browse on
the sea weeds which grow in the lagoon^ and breed there. Numerous
species of fish and shell-fish flourish in the same still water, which
abounds with animal life. Man comes at length and takes possession
of the island; and the cocoa-nut, the turtle, and the fish afford
him abundant and wholesome food. But you will ask how he sup-
plies himself with that necessary of life fresh water ? This is ob-
tained in a very simple and unexpected manner from shallow wells,
dug in the calcareous sand, which ebb and flow with the tides, yet
are almost wholly free from the saline particles of the ocean. Some
have supposed that the sea water lost its peculiar salts by infiltration
through the calcareous mass. Mr. Darwin thinks that it is derived
from the rain water, which, being specifically lighter than the salt,
keeps floating on its surface, and is subject to the same movements :
howsoever this may be, the fact is certain. A fit and convenient
abode for the human species is fabricated by the action of the feeble,
gelatinous polypes, and a wild and almost boundless waste of waters
is enlivened by oases which navigators have described as earthly pa-
radises.

A Barrier Reef {fig. 49. r% r) is essentially similar to the Atoll or
Coral-island. It runs parallel with the shores of some larger island
or continent ; separated, however, from the land;, by a broad and
deep lagoon channel (ii, ?i), and having the outer side as deep and

POLYPI. 91

steep as in the Lagoon Islands. Here likewise the skeletons of the
Zoophytes, of which the reef is composed, are found on the outer
precipitous wall as deep as sounding line can reach.

The third class of coral productions which Mr. Darwin terms
'' Fringing Reefs " {fg. 48. r, r), differ from the Barrier Reefs in
having a comparatively small depth of water on the outer side, and
a narrower and shallower lagoon channel between them and the
main land.

These differences in the characters of the wonderful fabrications of
the coral animalcules are explicable by the following facts in their phy-
siology. The animals of the Porites and Milleporce cannot exist at a
greater depth than twenty or thirty fathoms ; beyond this the stimuli
of light and heat derived from the solar beams become too feeble
to excite and maintain their vital powers. On the other hand, their
tissues are so delicate, that a brief direct exposure to the sun's rays
kills them ; and unless they are constantly immersed in water or beaten
by the surf, they cannot live. Thus, in whatever position the calca-
reous skeleton of a Madrepore or Millepore, may be found it is certain
that it must have been developed Avithin thirty fathoms of the sur-
face of the ocean. If it coats the summit of the lofty mountains of
Tahiti*, it must have been lifted above the sea by the elevation of the
rock on which it was originally deposited. If it is brought up from
the depth of 200 or 300 fathoms, as at Cardoo Atoll or Keeling Atoll,
it must have been dragged down to that depth by a gradual sub-
sidence of the foundation on which the living madrepore once
flourished. It is by these movements of upheaval and subsidence
of the earth's crust, that Mr. Darwin explains the different forms
which characterise the extraordinary productions of the coral animal.
The Atolls or Lagoon Islands, according to this author, rest on land
which has subsided, and part of which was once dry. Barrier' reefs
indicate the islands or continents, which they encircle, to be the
remains of land now partly submerged, and perhaps in progress
towards final disappearance. Fringing reefs^ on the contrary, indicate
either that the shores are stationary, or that they are now rising, as
in most of the Sandwich Islands, where former reefs have been raised
many yards above the sea.

Elizabeth Island, which is eighty feet in height, is entirely com-
posed of coral-rock. The coral animals, thus progressively lifted
above their element, are compelled to carry on their operations
more and more remote from the former theatres of their constructive
energies, but cannot extend deeper than their allotted thirty fa-
thoms : the direction of their submarine masonry is centrifugal

* Mr. Stutchbury here found a regular stratum of semifossil coral at 5000 ^and
7000 feet above the level of the sea.

92

LECTURE VII.

and descending. Where the land that supports them is, on the con-
trary, in progress of submergence, they are compelled to build their
edifices progressively higher and in a narrower circuit ; in other words
the direction of their growth is centripetal and ascending. The
terms ascending and descending of course only here apply to the re-
lation of the coral-builders to the land, not to the level of the un-
changing sea.

The formation of an atoll by the upward growth of the corals during
a gradual sinking of the land forming their supporting base is illus-
trated by these diagrams

48 from Mr. Darwin's work.

r .Sil

Figure 48. represents the
section of an island («, 5),
surrounded by a fringing
reef, r, rising to the surface of the sea, s. ]. As the land sinks
down, the living coral, bathed by the surf on the margin of the reef,
builds upwards to regain the surface. But the island becomes lower
and smaller, and the space between the edge of the reef, r, and the
beach proportionately broader. A section of the reef and island, after

a subsidence of several
hundred feet, is given in
figure 49. The former
living margin of the reef,
r, is now dead coral,
dragged down to depths at which the polypes cease to exist ; but their
progeny continue in active life at r\ now the margin of a barrier- reef,
separated by the lagoon channel n^ from the remnant of the land 6.
Let the island go on subsiding, and the coral reef will continue
growing up on its own foundation, whilst the water gains on the land,

until the highest point is
covered, and there re-
mains a perfect atoll, of
which figure 50. repre-
sents a vertical section.
In this diagram r'' is the
living and growing outer margin of the encircling reef, and the la-
goon channel is now converted into the calm central lake w, of the
atoll. Thus by the process of subsidence the fringing reef {fig. 48.)
is converted into the barrier reef {fig. 49.), and this into the atoll

{fig- 50.).

If the movement of the land should now be reversed, and the
level of the sea be again brought back by elevation of the island, to
the line (s. 1, fig. 50.), an island apparently composed exclusively
of coral rock, like Elizabeth Island, would be the res\dt.

BRYOZOA. 93

The prodigious extent of the combined and uninterniitting labours
of these little world-architects must be witnessed in order to be ade-
quately conceived or realised. They have built up a barrier-reef
along the shores of New Caledonia for a length of 400 miles, and
another which runs along the north-east coast of Australia 1000
miles in length. To take a small example, a single atoll may be
50 miles in length by 20 in breadth ; so that if the ledge of coral rock
forming the ring were extended in one line it would be 120 miles in
length. Assuming it to be a quarter of a mile in breadth, and 150
feet deep, here is a mound, compared with which the walls of Babylon,
the great wall of China, or the pyramids of Egypt, are but children's
toys ; and built too amidst the waves of the ocean and in defiance of
its storms, which sweep away the most solid works of man. The
geologist, in contemplating these stupendous operations, appreciates
the conditions and powers by which were deposited in ancient times,
and under other atmospheric influences than now characterise our
climate, those downs of chalk which give fertility to the south coast
and many other parts of our native island. The remains of the
corals in these masses, though similar in their general nature, are spe-
cifically distinct from the living Polypes which are now actively en-
gaged in forming similar fertile deposits on the undulating and half sub-
merged crust of the earth, washed by the Indian and Pacific Oceans.
Again, those masses of limestone rocks which form a large part of the
older secondary formations, give evidence, by their organic remains,
that they are likewise due to the secretions of gelatinous polypes, the
species of which perished before those that formed the cretaceous
strata were created. As the polypes of the secondary epochs have
been superseded by the Porites, Milleporce, Madreporce, and other
genera of calcareous Anthozoa of the present day, so these, in all
probability, are destined to give way in their turn to new forms of
essentially analogous Zoophytes, to which, in time to come, the same
great oflfice will be assigned, to clothe with fertile lime-stone future
rising continents.

LECTURE VIII.

BRYOZOA.*

If a deeper and truer insight into the structure and vital properties
of the low-organised, ramified, composite, hydriform polypes, which,

Ciliohrachiata, Farre.

94 LECTURE VIII.

like little trees adorned with polypetalous flowers and supporting
their annual crop of deciduous fruit or seed-capsules, deceived such
clear-sighted observers as Tournefort and Ray as to their real nature,
and were classed by them with vegetables ; if organised beings, so
obviously like plants in external form and in some of their most con-
spicuous changes, can be proved by the anatomist to belong un-
equivocably to the Animal Kingdom, without the determination
being vitiated or obscured by any real or essential vegetable charac-
ter:— if the calcareous masses of Madrepores and Millepores, classed
by Boccone and Guison as species of minerals, and which once were
the subjects of curious speculations on the growth of stones, have
been proved by the recognition of the more complicated organisation
of the polypes which they support, to be the products of the
vital actions of such polypes, and as essentially a part of those
animals as the skeleton of a man is a part of his body — still more
does the anatomical structure of the third division of polypes prove
how inadequate is a superficial survey of an organised being to lead
to true notions of its nature and affinities. The Bryozoa, which
coat, as with a delicate moss, fuci, shells, or other marine productions,
or which rise in dendritic forms, like the hydrozoic corallines,
with which they have been confounded by Ellis, with which they
would equally have passed for plants with Ray, are, perhaps, the
most striking examples of how comjDlicated an animal structure may
be masked by mere outward form.

An animal differs from a plant in having a stomach and a mouth,
it is thereby qualified to exert its most conspicuous animal property,
that of locomotion.

A locomotive organised being must possess an internal digestive
store-room ; but the converse of the proposition does not hold good,
— a digestive cavity does not imply the powers of locomotion.

The Bryozoon has not merely the characteristic digestive cavity,
like the Hydra and the Actinia : it has not merely a mouth and pre-
hensile organs for the capture of living prey ; but it has also an
oesophagus for deglutition, an intestine for the separation of the nu-
trient chyle, and a distinct external outlet for the indigestible refuse
of the food : it may possess a stomach w ith strong muscular walls and
a dentated lining for trituration, and a second stomach wdth glandular
walls for digestive solution or chymification, and thus present an ali-
mentary canal as complicated and as highly elaborated as in the bird.
Yet the microscopic polypes which manifest this high condition of the
digestive apparatus are fettered to the spot, w^here, as ciliated gem-
mules, they finally rested after their brief early locomotive stage : the

BRYOZOA.

95

complex digestive apparatus is developed for the service of an organ-
ised being as immovable as the plant which is rooted in the soil.

But we shall, hereafter, meet with animals of higher grade of
organisation than the Bryozoic polypes, as the Barnacle^ the Oyster,
and the Spondylus, which are equally fettered to the spot on which
they grow, and which more strikingly demonstrate how secondary
a character of animal life is mere locomotion.

The complicated and characteristic condition of the alimentary
canal in the Bryozoa was discovered independently, and nearly about
the same time, by Ehrenberg, Milne Edwards, and Dr. V. Thompson.
The ciliated structure of the arms was observed by Steinbuch and
Dr. Fleming. The ciliated gemmules, and their development, have
been well described in the Flustra carbesia by Dr. Grant. All these
observations have received a welcome confirmation, and many highly
interesting facts in the organisation and properties of the Bryozoa^
have been added, by Dr. A. Farre ; a careful perusal of whose ad-
mirable Memoir in the Philosophical
Transactions for 1837*, will amply
repay the reader.

Most of the Bryozoa are micros-
copic ; but, being composite or aggre-
gated animals, they sometimes form
sufficiently conspicuous masses. The
most familiar and common species con-
stitute the substance called sea-mat
(^Flustra), which incrusts, by its little
hexagonal cells, as by a delicate mo-
saic pavement, sea-weed, shells, and
other marine bodies. The calcareous
sea-mat is called Eschara. Some spe-
cies rise from their surface of attach-
ment and form amorphous masses, like
sponge ; or are regularly and delicately
ramified, like the little hydriform co-
rallines.

Each polype presents an oblong de-
pressed, or elongated and cylindrical
figure, and is protected by a dense in-
tegument in the form of a cell or case
{Jig. 51. «, ci), to the mouth of which
is attached a sac (6, h') composed of

Bowerbankia.

* P. 387. plates xx. to xxvii.

96 LECTURE VIII.

very delicate and flexible membrane. This constitutes the upper or
anterior integument of the polype when it is protruded, and is re-
flected, like the inverted finger of a glove, into the firmer portion
of the cell when the polype is retracted, as at B. In general the in-
tegument forming the firm cell is of a horny texture; but in the
Escharce it is hardened by the deposition of particles of carbonate of
lime in the organised animal basis; so that the external skeletons of
the Bryozoa offer analogous conditions to the cartilaginous and bony
states of the internal skeletons of fishes.

In the cylindrical Bryozoa^ as the Bowerhankia, the flexible part of
the integument consists of two portions ; the lower half being a simple
continuation of the cell ; the upper one consisting of a cylindrical
series of setae {b), connected together by an extremely delicate and
elastic membrane, permitting a certain extension of the cylinder,
which, at the same time, supports and allows free motion to the
upper part of the body in its expanded state. The mouth of the
polype is situated at this extremity of the body, and is surrounded by
a radiated series of slender, ciliated, tentacula (c), eight, ten, twelve,
or more in number, according to the genus.

The muscular system is developed in the present highly organised
class of polypes, in the form of distinct groups of fibres. Their ar-
rangement, and the actions by which they eff'ect the protrusion and
retraction of the polype, are minutely and clearly described by Dr.
Farre. The retractor muscles form two series, one acting upon the
alimentary canal, and the other upon the flexible part of the cell.
One series rises from the bottom of the cell, and is inserted about the
base of the stomach (c?) ; the other (e) arises from the opposite side of
the bottom of the cell, and passes upwards to be inserted near the base
of the tentacula. The muscles which retract the flexible integument,
arise near the upper margin of the cell, and are disposed in six
fasciculi, three of which act upon the membrane, and the other three
upon the bundle of setse by which it is crowned. When the animal
is retracted, the setae, which are drawn in after the tentacula, converge
and form a kind of defensive operculum. The oesophagus and intestine
are bent into folds.

The protrusion of the animal is eff'ected, partly by the action of
short transverse muscular filaments (e), which tend to compress the in-
closed viscera, and partly by the action of the alimentary canal itself.
The bundle of setae first rises out of the apex of the cell, and is
followed by the rest of the flexible integument : the tentacula next
pass up between the setae, and separate them ; the folds of the
oesophagus and intestine are straightened, and when the act of

BRYOZOA. 97

protrusion is completed, the crown of tentacles expands and their
cilia commence vibrating.

The advantage to Physiology of the researches of the comparative
anatomist in the minute forms of animal life, is often very great, in
consequence of the favourable conditions which the transparency of
the integument, and the distinctness of the contained parts of such
animalcules, afford for the direct observation of some of the most
recondite and important vital actions. As regards the Bryozoa, the
muscles are, as it were, naturally dissected or separated into their
component filaments. Each filament generally presents a small knot
upon its middle part : this is most apparent when the filament con-
tracts, at which time the whole filament is obviously thicker. When
the action ceases and the filament is relaxed, the distance between its
fixed points being diminished, as happens to the longitudinal fibres
when the polype is retracted into its cell, such fibre falls into undula-
tions. The thickening of the muscular fibre in the act of contraction,
and its folded state when it relaxes, before the antagonising muscles
have restored the extremities of the contracted fibre to their ordinary
distance, has been observed in other low organised animals, as small
Filarice. The higher organised subjects selected by MM. Prevost
and Dumas, were less favourable for this delicate experiment, and
they consequently mistook the zig-zag relaxation of the muscular fibre
for its act of contraction.

No trace of a nervous system has yet been detected in the Bryozoa;
but the reaction of stimuli upon the contractile fibre is a striking
phenomenon. The animal retires into its cell on the slightest alarm,
and refuses to expose itself to water which has become in the least
degree deteriorated. Dr. Farre has observed the creeping of a very
small animalcule over the top of one of the closed cells to be fol-
lowed instantly by the shrinking of the soft parts beneath. But the
nervous system is indicated in these little polypes by something more
than reflex phenomena : they seem to exercise a certain caution before
emerging from their cells. One or more of the tentacles have been
seen to be protruded and turned over the side of the cell, as if to
ascertain the presence or absence of an enemy.

I must now proceed to describe these tentacula (c, c), which are the
means by which the Bryozoa obtain their food. They differ con-
siderably from the corresponding tentacula in the Hydrozoa and An-
thozoa, in being stiff'er and provided with vibratile cilia. These cilia
are arranged on opposite sides of the tentacle, along which sides they
occasion, by their active vibration, opposite currents of the surrounding
water. In some species a few fine hair-like processes, which are mo-
tionless, project from the back of the tentacula. The action of the

H

98 LECTUKE VIII.

tentacular cilia appears under the control of the animal, and they are
sometimes seen completely at rest. The arms are tubular throughout,
and have an aperture at each extremity. The ring upon which they
are set forms a projecting edge around the mouth. The particles of
food are carried down the inner surface of each arm, and the mouth
and pharynx expands to receive such as are appropriate, as if by an
act of selection. The rejected particles pass out between the bases
of the tentacula, or are driven off by the centrifugal currents.

The pharynx {fig. 51, /) is less dilatable than the mouth of the
Hydra or Actinia, The constriction of the pharynx, by which the
food is driven into the oesophagus, is a very well-marked action.
The cardiac orifice {g) seems to project into the oesophagus upon a val-
vular prominence ; it opens into a small globular cavity (/;), which has
the construction of a gizzard : the interior of this cavity is lined
by a strong epithelium, the cells of which project into the cavity like
pointed teeth, and the food is subject to comminution in this cavity.
With the gizzard is associated, as in birds, a distinct glandular com-
partment of the stomach {i) ; but this is situated between the gizzard
and intestine, not between the gizzard and oesophagus : its walls are
studded with follicles filled with a rich brown secretion, which may
be regarded as hepatic follicles. The intestine is continued from a
distinct pyloric orifice (^), which is situated at the upper part of the
glandular stomach near the gizzard. This orifice is surrounded by
vibratile cilia. The food is frequently regurgitated into the giz-
zard, and, after having undergone additional comminution, is returned
to the stomach. Here it is kept in constant agitation, and the par-
ticles pass by a rotatory action from the pylorus into the intestine.
The indigestible particles are there formed into little pellets, which
are carried rapidly upwards to the anal orifice (Z), and, after being
expelled, are immediately whirled away in the current produced by
the ciliated tentacula.

A small filament, conjectured to be tubular, which passed from the
base of the glandular stomach to the common stem (iii) supporting the
cell of the polype, is the only trace of the nutrient or vascular system
which Dr. Farre could detect. When the common stem of a
ramified Bryozoon is cut across, it seems to be nearly homogeneous, and
does not present that obvious distinction between hard and soft parts,
nor the canal with circulating particles, which are observed in the
stems of the compound Hydrozoa. Yet it can scarcely be doubted
but that nutrient currents must traverse the common connecting
organic medium or stem of the Bryozoa, both for its own support and
growth, and for the supply of the means of growth to the young
animals (C) which are developed from it by the process of gemmation.

BRYOZOA. 99

The function of respiration must be referred to that part of the
body which is provided with the means of effecting a constant re-
newal of the surrounding oxygenized medium upon its surface. In
the ciliated tentacula, whose currents. Dr. Farre observes, seem much
beyond what is necessary to afford a sufficient supply of food, we,
therefore, recognise the principal respiratory as well as prehensile or-
gans. The currents of the nutrient fluids which may traverse their
interior canal would thus be more effectually exposed to the influence
of the surrounding medium.

The individuals of the Bryozoa are multiplied by two processes of
generation ; the one by gemmae or buds from the common stem, which
appears to be uninfluenced by season, and which increases the size of
the aggregate mass of the Bryozoon ; the other by the liberation of
the young in the form of locomotive ciliated gemmules, which takes
place at certain seasons, generally in spring.

In the Flustra the gemmee are developed from the cells of the
pre-formed individuals ; but in those Bryozoa which have connecting
stems the buds arise from the stem. They are at first homogeneous ;
then a distinction may be observed between the cell (^Jig- 51. C, a)
and the visceral contents (b) ; afterwards the tentacles may be dis-
cerned, which are at first short and stumpy ; finally, the cavity, walls,
and divisions of the alimentary canal become distinguishable.

In regard to the generation by locomotive gemmules, these are
doubtless originally developed from fertile ova.

Certain phenomena have been observed in the Bryozoa which
justify the belief that the individual polypes are male and female.
Dr. Farre has figured a specimen of the Valkeria cuscuta, in which he
observed a very remarkable agitation of particles in the visceral
cavity, caused by a multitude of minute cercarias swimming about
with the greatest activity in the fluid with which that cavity is filled :
they consisted simply of a long slender filament with a rounded ex-
tremity, by which they occasionally fixed themselves. Similar moving
filaments were not un frequently observed in other species. On one
occasion Dr. Farre observed them in a specimen of HalodactyluSy
drifting rapidly to the upper part of the visceral cavity, and issuing
from the centre of the tentacula, indicating an external communication
with the cavity of the body. The analogy of these cercariee with the
spermatozoa discovered by Wagner in the tortuous generative tubes
of the Actinia, indicates their real nature and importance in the
generative economy of the Bryozoa.

The development and vital phenomena of the reproductive gem-
mules have been studied with most completeness in the Halodactylus.
They appear in spring as minute whitish points just below the surface,

H 2

100 LECTURE VTII.

If one of these points be carefully turned out with a needle, it is found
to consist of a transparent sac, containing generally from four to six
of the gemmules. These are of a semi-oval form, with the margin of
their plain surface developed into tubercles supporting groups of
vibratile cilia. The body presents a simple granular structure ; the
gemmule swims about actively by the vibration of its cilia, the motion
of which seems to be under its control. They generally swim with
the convex part forwards ; sometimes they simply rotate upon their
axis, or execute a series of summersets ; or, selecting a fixed point,
they whirl round it in rapid circles, carrying every loose particle after
them ; or they creep along the bottom of the vvatch glass upon one
end with a waddling gait : but at the expiration of forty-eight hours
they attach themselves to the surface of the glass, and the rudiments
of a cell may be observed.

In the Flustra, the gemmules are developed between the cell and
the body of the polype, which yields to, and is destroyed by, them
as they are developed. These likewise escape, and, after a short term
of locomotive life, settle and subside, the outline of the cell being first
formed, and the polype with its tentacula, muscles, and alimentary
canal being afterwards developed in a distinct small closed sac.

There are a few genera of fresh-water polypes, as the Plumatella
and Cristatellay which have the ciliated tentacula in the form of cres-
centic or horse-shoe lobes. The Cristatella has been observed to
produce ova of a flattened discoid form, with their outer surface sin-
gularly beset with long bifurcated hooks like the infusorial Xarithidia.
The young Cristatella undergoes its metamorphosis from the ciliated
gemmule-state to the mature form of the polype in the ovum, from
which it escapes by splitting it into two parts.

In thus tracing upwards the organisation of the animals which
present the common external character of a circle of radiated oral
tentacula, we have met with modifications of anatomical structure
which clearly indicate three classes, and conduct us from a grade of
organisation as low, at least, as that of the monad, to one as high as
the wheel-animalcule. We have already seen that certain forms cf
the Rotifera, as the Stephanoceros, combine the external character-
istic of the Bryozoa, as the cell and ciliated tentacula, with an equally
complicated type of internal organisation ; but no rotiferous animal
developes buds. The Bryozoa still retain this common characteristic
of the whole race of polypi.

The Bryozoa make a still closer approximation to the compound
Ascidians, which form the lowest step of the molluscous series ;
but in the compound Mollusca we find the ciliated tentacles re-
reduced to mere rudiments at the entrance of the alimentary canal ;

ACALEPH^. 101

whilst the pharynx, or first division, is disproportionately enlarged
and, being highly vascular, and beset with vibratile cilia, performs
the chief part of the respiratory function.

But before proceeding to the great primary group of hetero-
gangliate animals, to which we are thus conducted, it will be
necessary first to consider the larger forms of Radiata, which seem
to diverge from the Anthozoic division of the Polypi of Cuvier.

LECTURE IX.

ACALEPH^.

CuviER, after having allocated a certain proportion of the Vermes of
Linnaeus in his two great primary groups, Mollusca and Articulata,
left the remainder to form a fourth sub-kingdom of animals under
the name of Radiata^ of which we have now to consider the highest
organised species.

It is true that the animals which last occupied our attention have
a radiated arrangement of the prehensile organs about the mouth ;
but the only classes containing species with a radiated form of the
entire body, are those to which the term Radiaria has been applied
by Lamarck. These are animals of more complicated organisation
than the Anthozoic polypes, the large, soft, gelatinous species of
which lead to the still larger, softer, and more gelatinous forms of the
present class.

The true radiated Invertebrata have been divided into two groups,
according to the nature of their integuments, which, in the one, is
soft and gelatinous, in the other coriaceous, or calcareous, and ge-
nerally armed with spines. The species of both classes are aquatic
and marine, and both are extensively diffused through all the climates
of the globe. The soft-bodied Radiaria float in the free and open
sea : to the shores and fathomable depths are limited the better
defended groups, as being better able to bear the brunt of the cease-
less conflict between land and water.

The gelatinous oceanic Radiaries are remarkable for the singularity
and beauty of their forms and colours : they give variety and animation
to the otherwise monotonous waste of waters which are most remote
from land. They there surprise and delight the weary navigator by
their mimic fleets, glistening with all the brilliant hues of the rain-
bow. They tantalise the naturalist-collector both by their bright

H 3

102 LECTURE IX.

colours and the pure, glassy, transparency of their tissues, which
baffle all his arts of preservation, and can never be displayed in the
cabinet. They often leave upon the unwary hand of the captor pun-
gent evidence of their singular power of inflaming the skin. It is this
stinging or urticating property which has procured for the " Radi-
ares Mollasses" of Lamarck the name of AcalephcE amongst the
ancient Greek naturalists, and " Sea nettles " from our own fisher-
men and sailors.

The Acalephce are represented on the British coasts by numerous
discoid and spheroid gelatinous animals, varying in size from an
almost invisible speck to a yard in diameter, known by the name of
" Sea blubber," " Jelly fish," or by the Linnaean generic term
" Medusar

Occasionally some of the singular forms of Acalephce of the tropical
seas are stranded on the south-western shores of England. I have
picked up on the coast of Cornwall the little Velella, which had
been wafted thither, unable to strike its characteristic lateen-sail.
There also I have seen wrecked a fleet of the Portuguese men-of-war
(JPhysalia), which had been buoyed by their air-bladders to that
iron-bound coast.

The most characteristic features in the organisation of the Aca-
lephae, may be exemplified by the anatomy of the larger Medusce of
our own seas.

The first thing which astonishes us in commencing the dissection
of these creatures is the apparent homogeneity of their frail gelatinous
tissue; secondly, the very large proportion of the body, which seems to
consist of sea water, or a fluid very analogous to it : for let this fluid
part of a large Medusa, which may weigh two pounds when recently
removed from the sea, drain from the solid parts of the body, and
these, when dried, will be represented by a thin film of membrane,
not exceeding thirty grains in weight. The art of the anatomist would
seem to be baffled by the very simplicity of his subject, instead of, as
in other cases, by the inability to pursue and unravel all the intricate
combinations of the created mechanism. Peron and Lesueur, two
experienced French naturalists, who, during the circumnavigatory
voyage to which they were attached, paid great attention to the
floating Acalephce^ have thus summed up the results of their ex-
perience in regard to their organisation. " The substance of a
Medusa is wholly resolved, by a kind of instantaneous fusion, into a
fluid analogous to sea water ; and yet the most important functions
of life are efi'ected in bodies that seem to be nothing more than, as it
were, coagulated water. The multiplication of these animals is pro-
digious; and we know nothing certain respecting their mode of

ACALEPH^.

103

generation. They may acquire dimensions of many feet diameter,

and weigh occasionally from fifty to sixty pounds ; and their system

of nutrition escapes us. They execute the most rapid and continued

motions ; and the details of their muscular system are unknown.

Their secretions seem to be extremely abundant; but we perceive

nothing satisfactory as to their origin. They have a kind of very

active respiration ; its real seat is a mystery. They seem extremely

feeble, but fishes of large size are daily their prey. One would

imagine their stomachs incapable of any kind of action on these

latter animals : in a few moments they are digested. Many of them

contain internally considerable quantities of air; but whether they

imbibe it from the atmosphere, extract it from the ocean, or secrete

it from within their bodies, we are equally ignorant. A great number

of these Medusae are phosphorescent, and glare amidst the gloom of

night like globes of fire ; yet the nature, the principle, and the agents

of this wonderful property remain to be discovered. Some sting and

inflame the hand that touches them; but the cause of this power is

equally unknown."*

In this series of lively paradoxes, the general and obvious charac-
ters of the AcalephcB are strikingly exemplified, and the observers^
labouring under the disabilities and inconveniences of shipboard life,
may be excused if they failed to solve problems of such unusual
difficulty.

With respect to the organs of nutrition of the Medusae, let us see

what Hunter was able to de-
monstrate, and leave for our
instruction. In these speci-
mens f, which belong to the
genus Rhizostoma, he has in-
serted his skilful injecting ap-
paratus into the stomach {Jig.
52, «), plunged, so to speak, " in
medias res," and made conspi-
cuous by his coloured injection,
both the extraordinary route by
which the nutriment reaches the
digestive cavity, and also the
channels by which the digested
aliment is distributed for the
support of the general system.

52

Rhizostoma.

* Annales du Museum, torn. xiv. p. 219.
t Nos. 847. 982, 983.

H 4

104 LECTURE IX.

The oesophagus (b) divides into four canals (c), which enter the
base of four processes (p, p), which are continued from the centre
of the under part of the animal's body. These peduncles divide
and subdivide like the roots of a plant ; the oesophageal canals
follow these ramifications, and ultimately terminate in numerous pores
(d, d), upon the margins of the branches and clavate ends of the
ramified peduncles. These pores are, in truth, the commencement
of the nutritive system ; they are, in this respect, analogous to the
numerous polype-mouths of the compound coral zoophyte ; but in the
Rhizostome a common central sac is interposed between the ingestive
conduits and the vascular system of the body. Minute animalcules, or
the juices of a decomposing and dissolving larger animal, are absorbed
by these pores, and are conveyed by the successively uniting oeso-
phageal canals to the stomach. Digestion being completed, the chyle
passes at once into the vascular system, which is in fact a continua-
tion and ramification of the gastric cavity. The nutrient fluid passes
by vessels (e), which radiate from that cavity, to a beautiful net-
work (/, /) of large capillaries, which is spread upon the under
surface of the margin of the disc. The elegance and precision with
which the injections of Hunter have demonstrated this network in
his preparations cannot be surpassed ; but it is to Cuvier that we owe
the first description of the very remarkable and interesting system of
nutrition in the Rhizostome.*

The rich development and reticular disposition of this part of
the vascular system, in which the circulating fluids are exposed
to the surrounding medium in a state of minute subdivision, upon
that surface of the body which rests upon the water, prove that
the respiratory interchange of the gases, and the absorption of the
oxygen from the air contained in the sea water, take place prin-
cipally at this vascular surface of the gelatinous disc; and that
Hunter is correct in placing it amongst the series of respiratory
organs. It stands, indeed, at the lowest step of that series, since the
organ is not specially eliminated, but only indicated or sketched out,
as it were, by a modification of part of the common integuments.

In the CyancBa aurita, another species of our coasts, another
modification of the digestive system has been detected. The digestive
sac {fig- 53, a) opens immediately upon the under surface of the body
by a single four-lipped mouth ; sixteen canals radiate from the central
cavity, eight of which (b, b) form, by their ramifications, the systems of
nutrient and respiratory capillaries ; whilst the alternate eight terminate
without dividing, each by a minute orifice or anus (c) at the margin
of the disc.

* Journal dc Thysiquc, torn, xlix, 1799, p. 436.

ACALEPHuffi.

105

We must suppose the mouths of these excretory vessels to be
endowed with an irritability of a different kind from that of the
nutrient canals, like the mouths of the different cavities of a ruminat
ing stomach. For, as the orifices of the third and fourth stomachs

contract upon the coarse
unmasticated food, whilst
those of the first and se-
cond open to receive it,
and close when it is pre-
sented to them in its re-
masticated state, so the
nutrient diverticula of the
stomach of the Cyansea re-
ceive the digested and ex-
clude the excrementitious
part of the food, which
passes along the anal ca-
nals, and is thus rejected
from the system. But, it
cyansea. may asked, why the Cy-

ansea should have intestines and vents, whilst the Rhizostoma has
neither ? The difference, doubtless, relates to the different organis-
ation of their mouths. In the Rhizostoma, only finely comminuted
matter, as animalcules and fluids, can obtain access to the digestive
sac ; no solid excrements are formed, or require to be expelled ; but
the Cyanaea with its single and larger mouth can swallow Crustacea
and small fishes.

The discovery of the precise condition of the nutrient apparatus
in the CyaricBa aurita is due to the ingenuity and perseverance of
Prof. Ehrenberg, who induced the living animals to swallow indigo
with their food. He has represented the canals so injected, in the
elaborate plates of his memoir on the anatomy of this species.*
Prof. Wagner f saw the currents of the nutrient fluid in the vascular
system of the Oceania : they were produced, not by contraction of
the canals, but by the vibration of the cilia lining them.

The Medusae swim by the contractions of the margin of their
gelatinous disc ; and Mr. Hunter has put up a corrugated portion of
the disc J, which he seems to have considered as indicative of the ar-
rangement of muscular fibres of the part. Prof. Wagner states that
the muscular fibres which he detected in Oceania and Pelagia, had

* Abhandl. der Konigl. Akad. der Wissen zu Berlin, 1 835.
f Ueber den Bau der Pelagia noctiluca, fol. 1841
\ No. 55.

106

LECTURE IX.

the transverse striae which characterise the ultimate fibres of the
voluntary muscles in the Vertebrata.* In the integument of the Pelagia
he distinguishes an outer epithelium, and beneath this pigmental cells,
with small colourless vesicles in their interspaces : each of these vesi-
cles contains a spiral filament, the fine extremity of which projects from
the surface, and is probably the duct of the gland, which Ur. Wagner
conceives to be the organ of the urticating property. He does not
find these spiral glands in the Cassiopeia, which does not sting.

Ehrenberg has detected and figured certain coloured specks (c?)
placed at definite distances round the margin of the disc of the
Cyanaea, which he regards, with much probability, as organs for the
special reception of the stimulus of light. He finds each ocellus con-
nected with a small ganglion or mass of nervous matter, from which
delicate filaments may be observed to radiate, which probably form
a nervous circle around the margin of the disc. Nothing more au-
thentic has been observed relative to the muscular or nervous systems
of the Medusae. These Acalephae, which swim by the contraction of
this muscular and vascular margin of their body-disc, have been
termed " Pulmogrades."

With respect to the Acalephae which enjoy other modes of loco-
motion, and especially those that swim by the action of superficial
vibratile cilia, very conflicting evidence has been adduced of their
nervous system.

Dr. Grant-]- has described and figured a double filamentous chord
connecting a chain of eight ganglions around that extremity of the
Beroe {Cydippe) pileus {fig.5^yb)i from which the two long cirri-

gerous tentacula (c? d) are pro-
truded. Whatever analogy such
nervous system may bear to that
of the Echinoderms in the cir-
cular disposition of the central
filaments, and the radiation of
nerves from that centre, it has
none in regard to its situation,
for the mouth of the Beroe (a)
is at the opposite end of the
^^"^PP" body.t

Dr. Milne Edwards § describes and figures part of the nervous
system in a larger species of Beroe {Lesueura vitrea) as radiating

* Loc. cit.

t Zool. Trans, vol. i. p. 10. PI. 2. fig. 1.

i Forbes, in Annals of Natural History, vol. iii. p. 149.

§ Annales des Sciences Nat. n. s. torn, xvi. p. 206. PI. 4.

ACALEPH^.

107

Cydippe.

from a single small ganglion, which is closely connected with a
coloured eye- speck, situated at the middle of the superior extremity
of the body.

The principal locomotive organs in the Beroe consist of unusually
large cilia, aggregated in lamelliform groups (^Jigs. 54 and 55, c c),

which seeming plates are arranged, like
the paddles of a propelling wheel, along
eight equidistant bands, extending along
^he surface from near one end of the
body to near the other.

The organs by which the Beroe can
attach itself to, or poise its body on, a
solid surface, are the two long tentacles
which are fringed with spiral cirri.
These tentacles can be entirely with-
drawn into the two cavities g, g, which
extend along each side of the slender intestine /. This is continued
from the simple elongated vertical digestive sac (e), the form of
which, in transverse section, is shown in Jig. 55. The Acalephse,
which, like the Beroe, swim by the action of vibratile cilia, are termed
" Ciliogrades."

The Physalia or Portuguese man-of-war has a large air-bag to aid
its swimming ; the Physophora floats by many smaller air vesicles :
the species so provided are called " Hydrostatic Acalephae."

Two genera of Acalephse have an oval or circular gelatinous body
supported by an internal solid, cartilaginous, or albuminous plate :
numerous extensile tentacles or cirri depend from the under surface
of the body, in the centre of which is the mouth. These form the
order " Cirrigrades." There is no evidence, however, that they swim
by any action of their prehensile cirri. One of the genera, Velella,
has a process of the firm internal skeleton, rising from the upper sur-
face of the body- disc or deck, to which it is set at the same angle as
the lateen-sail of the Malay boat : it is wafted along by the action
of the wind upon this process, and may have been mistaken for the
fabled Cephalopodic paper-sailor (^Argonautd).

The generative system and the development of the ovum in the
Medusae have received very satisfactory elucidation by the observa-
tions of Gaede, Cuvier, Ehrenberg, Sars, Siebold, and Wagner.

Propagation by gemmation has been observed in the pulmograde
genus Cytaeis. An incomplete gemmation takes place in Stephanonia
and others ; but this simple vegetative mode of propagation, which
is so common in the lowest Infusories and Polypes, is here the ex-
ception.

The Medusae are highly prolific, and propagate in the ordinary

108 LECTURE IX.

manner of animals from impregnated ova, the germs of which are
developed in organs or ovaria peculiar to one set of individuals, while
the fertilising filaments are prepared by testes peculiar to other indi-
viduals ; the Acalephae being male and female or dicBcious. The
generative organs in Rhizostoma, Cyanmay and many other Medusae,
are situated in both sexes in four cavities (^fig^ 53. e, e), which open
on the under part of the disc, near the mouth. The testes and
ovaria have the same form and colour, but are different in structure.
The females of Cyanma aitrita are distinguished by having numerous
small flask-shaped sacs developed from the under surface of the oral
peduncles or arms. The sexes do not differ in size.

Each testis consists of a plicated band of membrane, bent in the
form of a bow, with the convexity attached to the concave wall
which divides the generative cavity from the stomach. If a probe
be inserted in the generative cavity, it immediately touches the
under surface of the testis ; if it be inserted in the digestive cavity,
it touches the upper surface of the testis, but not immediately, be-
cause the epithelium of the digestive cavity covers that surface.
The testis is much longer than the cavity containing it, but is adapted
thereto by its numerous convolutions. Its concave side gives off a
numerous series of highly irritable coloured tentacles, having the
same structure as those on the arms. They are richly ciliated,
and contain many peculiar hyaline rounded corpuscules immediately
beneath the surface. The spermatic tentacles are capable of only
moderate extension, and, at the breeding season, they project from
the mouth of the generative cavity, leaving only a small passage at
their centre. By their powerful ciliary apparatus they keep up a
strong current of sea water, and thus aid in the expulsion of the
semen.

The parenchyma of the testis consists of a transparent granular
substance, in which are imbedded innumerable pyriform sacs, having
their bases turned towards the upper surface of the testis, and their
apical orifices opening upon their under surface, which they render
uneven by their tumid margins. The spermatozoa are developed in
these sacculi, which permanently represent the earliest rudiments of
the extremely elongated seminal tubes in the higher animals. The
parietes of the seminal sacs are pretty thick, and perhaps contractile.
A terminal enlargement, or body, and a ciliated appendage may be
distinguished in the spermatozoa : the latter part manifests an undu-
latory movement. The fasciculus of spermatozoa does not exhibit
these parts, in the same degree of development, in each sperm sac.
Those nearest the cervix of the sac are the most perfect. The ciliary
appendages of the spermatozoa are always directed towards the
opening of the sperm-sac. The bundles of these filaments follow each

ACALEPH^. 109

Other, and frequently the apical tails of one are infixed in the' cen-
tral interspace of the bodies of the preceding bundles ; and a chain or
string of bundles of spermatozoa are thus formed, which are easily-
detected by a moderate microscopic power.

In Cyanaeae of an inch and a half in length, the males may be dis-
tinguished by the sperm sac in the plicated testis ; and the females by
the germinal vesicle and spot in the corresponding ovarium. But
the band-like genital organ in both is small, and the folds are indi-
cated by slight risings and depressions.

The ovarium, like the testis, consists of a band with many folds
attached to the septum dividing the generative from the digestive
cavity. Its concave border is beset with similar tentacles ; but the
thin epithelium, on the under surface of the ovarium, is here and
there slightly ciliated, which has not been observed in the testis.
The tissue of the ovarium is looser, and it has more the aspect of a
cavity, than the testis. The minutest germs of the ova are nearest
that surface of the ovarium which is attached to the membranous
septum ; the most mature ova are on the opposite or free surface,
from which they project, covered only by a very thin membrane, and
giving it a coarse granular character.

The ova at first consist of a germinal vescicle with its spot or
nucleus. They increase in size by the addition of a violet-coloured
yolk. In this state they are transferred from the ovarium to the
marsupial vesicles on the under surface of the arms ; but how they
get there is not known : they are doubtless impregnated " in transitu."
In the ova of the marsupial sacs, Siebold could no longer discern
the germinal vesicle, and he conceived, in conformity with the pre-
valent notion, that that important body had been destroyed as the
first effect of fecundation. No doubt its primitive character had been
altered and obscured by the cell-building processes which had ra-
diated from its nucleus, like those observed by Dr. M. Barry in the
ovum of the rabbit.

The marsupial ova next assume an increase of size, and the yolk

begins to divide, by a spontaneous fission, which Dr. Siebold* describes

as commencing by a lateral indentation, as mfig. 56., which proceeds

56 57

Medusa.

across until the bipartition is complete, as in Jig. 57. At all events,

the vitelline mass is divided into two parts. Subsequent subdivisions,

analogous to those of the ova of the Strongylus (p. 77.), are de-

* Beitrage zur Naturgesch. der Wirbellosen Thiere, 4to. 1839.

no

LECTURE IX.

scribed and figured by Dr. Siebold, from whose Memoir I have selected
the four-fold {fig. 58.) and the eight-fold {fig. 59.) generation of
yolklets represented in the diagrams. These are progressively multi-
plied by fissures, which are represented as proceeding by a diverging or
radiating course from the centre, until the whole surface of the vitelline
mass presents a granulated character. And now the ovum loses its
violet colour and transparency, and becomes a dark yellow. The mem-
brana vitelli acquires an epithelium {fig. 60, a) of the same colour, on
which traces of cilia are perceptible. These at length cover the whole
ovum, which may then be said to have taken on its embryonic
state. A cavity (6) is next observed to be developed in the centre
of this yellow-coloured ciliated gemmule. It rapidly changes the
round for the oval form, and then becomes elongated like the infu-
sorial Leucophrys {fig. 61.). In this state it quits the maternal pouch,
and swims with the great end foremost. The liberated and locomotive
young Medusse sometimes re-enter the generative cavity, and get en-
tangled between the folds and tentacles of the ovarium, which led
Ehrenberg to describe them as ovarian ova ; but Dr. Siebold observes,
that if they were produced there as gemmules with the power of
swimming, the marsupial sacs, in which they actually acquire that de-
velopment, might have been dispensed with.

The young Medusa, having swam through its polygastric stage,
attaches itself to some firm body, preparatory to its next metamor-
phosis. The great or cephalic end is shortened and thickened, and a
depression is observed in its centre, which is the commencement of a
digestive cavity ; then the margin of this cavity expands, and is deve-
loped into four processes, richly furnished with vibratile cilia {fig. 62.).
A small cavity or disc for adhesion is formed at the opposite extremity
of the body, and thus the metamorphosis from the polygastric to the
rotiferous form of infusory is effected in the embryo Medusa. During
these changes the yellow colour is lost, and the body becomes

colourless and transparent ; it
also manifests a more general
irritability, sometimes elon-
gating, sometimes contracting
itself.

Four other ciliated cephalic
processes or arms next ap-
pear in the interspaces of the
first four, and all increase in
length ; these eight arms have
the power of remarkably short-
cyanaea. cuing and elongating them-

ACALEPHiE. 1 1 1

selves, as at a and h.jig. 63.; their superficial cilia create vortices in
the surrounding water, v.hich carry the nutritive molecules to the
mouth of the young Medusa, which is now metamorphosed into an
eight-armed ciliobrachiate polype. The arms or tentacula are very
like those of the ovaria and testis in the adult. Their cilia are not
placed in two regular rows as in the true Bryozoa. They contain
clear corpuscules, arranged in regular bracelets, as in the tentacles
on the margin of the disc of the fully developed Medusae. The
whole tissue is highly contractile ; the change from the extended
state («, a) to the contracted one (6, 6) is instantaneous when the
polype is irritated. The mouth of the polype-shaped young is very
contractile and expansible ; they feed on Infusoria and on their in-
fusory-like younger brethren, one half of whose body may often be
seen hanging out of the mouth of the little devourer.

The young Medusae remain in the polype state five months, from
September to the following February, and probably attach them-
selves to rocks in the more tranquil depths of the ocean during the
stormy months of winter. M. Sars, who confirms the preceding ob-
servations of Dr. Siebold, has traced the remainder of the meta-
morphoses of the Medusa.* The number of tentacula is augmented
by the development, in October, of additional ones in the interspaces
of the eight primitive series : the body increases, but more in thick-
ness than in length ; it even developes buds, which grow into young
polypes, with the power of completing their change into the Medusa
state, — that change being essentially a subdivision of the thickened
body of the many-armed pseudo-polype by spontaneous transverse
fission, at several equidistant points, into from ten to fifteen young
Medusae, which present the form described and figured by M. Sars in
1829 as a new genus of Acalephan, under the name of Strobila,
This most extraordinary process takes place in February. It was
observed by Sir J. G. Dalyell in 1835-|-, and described as one of the
generative phenomena of the Hydra tuba, under which name that
acute observer had designated the polype-like larva of the Medusa.
The Hydra tuba is not, however, the masked form of one, but the
potential aggregate of numerous Medusae. We thus see that a Me-
dusa may actually be generated three successive times, and by as
many distinct modes of generation, — by fertile ova, by gemmation,
and by spontaneous fission, — before attaining its mature condition.
When finally liberated by the third and last process they rise to
the surface, and swim about as small Medusae, rapidly increasing

* Archiv. fur Naturgesch. 1841, p. 9-

f Edinb. New Philos. Journal, vol. xxi. I8;36, p. 92.

112 LECTURE X.

in size under the influence of the light and warmth, and the abundant
food, which result from the stimulus of the rays of the summer sun
upon the surface of the ocean.

In comparing the several stages in the very interesting development
of the Cyancea aurita to the Infusoria and Polypes, it must be under-
stood that such comparisons are warranted only by a similarity of
outward form, and of it\^ instruments of locomotion and prehension.
The essential internal organisation of the persistent lower forms of
the Zoophyta is entirely wanting in the transitory states of the higher
ones. A progress through the inferior groups: is sketched out, but
no actual transmutation of species is effected. The young Medusa,
before it attains its destined condition of maturity, successively
resembles, but never becomes, a Polygastrian, a Rotifer, and a Bryo-
zoon.

LECTURE X.

ECHINODERMA.

The soft and gelatinous Radiaries have often baffled the anatomist
by the seeming simplicity and uniformity of their texture; the
harder, spine-clad, or Echinodermal species, perplex the most patient
and persevering dissector by the extreme complexity and diversity of
their constituent parts.

This class of animals, the organisation of which I shall endeavour
to explain in the limits of the present Lecture, includes species in
which the form is most strictly or typically radiate : in it, also, the
Zoophyta of Cuvier attain their highest conditions of organisation.
With a radiated filamentary system of nerves, we find not only a
distinct abdominal cavity with an alimentary canal suspended therein
by a vascular mesentery, and having a distinct anal outlet, but like-
wise a large and well-defined respiratory organ. This organ, how-
ever, may be regarded as the exceptional condition of the radiated
type of structure, and is found only in the highest and aberrant forms
of the present class, which indicate the transition from the Echino-
derms to the Annelides. At the opposite extreme of the Echinoderma,
the digestive sac (^^.,64. a), though suspended freely in an abdominal
cavity, has yet but one aperture common to the reception of food
and the ejection of excrement. These anenterous Echinoderms belong
to the family (^S teller idee) ^ in which the radiated form is most complete

ECHINODERMA.

113

and general, whence the sjDecies have received the common appellation
of star-fish.

Asterias.

In certain Stelleridm we trace a shortening, flattening, and expan-
sion of the rays, until the body assumes a pentangular discoid form. In
the next family {Echiriidce), the angles disappear, and the disc expands
until a spheroid or globular form is obtained, which characterises the
Echinoderms commonly called " Sea-urchins," and Echinoi by the
Greeks.

The third tribe of Echinoderms {Holothuriidce) may be described as
being constituted by a softening of the calcareous skin of the sphe-
roidal species, the globe being then drawn out by the two opposite
poles into an elongated cylindrical form. These vermiform Echino-
derms conduct to the true worms, which stand on the lowest step of
the Articulate division of the Animal Kingdom.

The name Eckinoderma has been applied to these diversified forms
of the higher organised Zoophytes of Cuvier, because in many of the
species the integument is defended by spines : they, however, possess,
and are associated together by, another and more general tegumentary
character ; the skin is perforated in most of the species by minute

114 LECTURE X.

foramina, throngli which a multitiule of small tubes or hollow ten-
tacula can be jDrotruded and retracted, and these constitute the
common organs of adhesion and locomotion in the Echinoderms.

Before conmiencing the demonstration of the principal characters
of the StelleridcB, or Star-fishes^ I may observe that in one existing
species of an allied family (^Crinoidem), the radiated disc is fixed by
a long jointed stem to some foreign body, as you perceive in this
Pentacrinus Caput Medusa, the type of a very numerous assemblage
of analogous pedunculated star-iishes, which existed in countless my-
riads during some of the ancient periods of geology : their remains
sometimes constitute extensive tracts of marble-limestone, and are
known by the names of Stone-lilies, or Encrinites.

The stem is composed of numerous joints or segments having a
central aperture, which, when insulated, are called wheel-stones, or
"Entrochi;" casts of their cavity remaining after the calcareous
walls have been dissolved away constitute the " screw-stones " of the
Derbyshire chert, and other transition limestones. The jointed column
supports at its summit a series of plates forming a cup-like body,
containing the viscera, and from whose upper rim proceed five jointed
arms, which radiate and divide into delicate tentacula. The upper
side of the arms support numerous short jointed cirri. Groups of five
long and slender cirri radiate at nearly equidistant points from the
stem of the recent species.

The form of star-fish to which the radiated capital of the crinoideal
column bears most resemblance is that which is presented by the
species of Comatula, the ova of which have been discovered by
Dr. V. Thompson to pass through a pedunculated pentacrinite state,
before their final metamorphosis into a free star-fish.

In the condition of their digestive system, the Pentacrinites and
Comatulae correspond with the Bryozoa among the polypes. The
Pentacrinus may be regarded as a gigantic form of pedunculated
Bryozoon. The free Comatula is a step in advance, and manifests
its affinity to the gelatinous Radiaria by its mode of swimming :
the movements of its pinnate arms exactly resemble the alternating
stroke given by the Medusa to the liquid element, and with the same
effect of raising the animal from the bottom, and propelling it back
foremost.

The rays of the ordinary star-fishes are not cirrigerous or bifur-
cated : their soft external integument is supported by a tough co-
riaceous membrane, strengthened by calcareous matter disposed in
a coarsely reticulate form upon the dorsal and lateral aspects of the
radiated body, and arranged in series of more compact and regu-
larly-formed transverse pieces, which bound each side of a lon-
gitudinal furrow, extending along the under surface of each ray

ECHINODERMA. 115

from its attached to its free extremity. The sides of this groove are
perforated by alternating rows of minute foramina, and external to
these are situated the largest and most numerous spines.

The tubular feet or tentacles are protruded through the marginal
pores of the furrows, which are termed Ambulacra. These feet have
muscular parietes, and they communicate with internal vesicles, full of
fluid, which form, in fact, the bases of the feet. By the contraction of
the parietes of the vesicle the fluid is injected into the tentacle, and
protrudes and extends it : when the muscular parietes of the tentacle
contract, the fluid is returned into the sac, and the tentacle is
shortened and retracted. The basal vesicles are in communication
with, and are supplied by, a system of tubes and larger pendent
pyriform sacculi, which are lodged in the central disc or body of the
star-fish, and surround the oral aperture.

There are other kinds of soft contractile appendages to the integu-
ment, some tufted, others of simple form ; but the tentacula just
described are the most important organs for prehension and locomotion.
The tegumentary processes called " pedicellarise," which resemble
miniature pincers, will be more particularly described in connection
with the skeleton of the Echinus.

There are certain species of star-fish called OphiurcB, in which the
rays are extremely attenuated and elongated, and have neither am-
bulacral grooves nor tentacula. Nor is this complicated mechanism
here needed, for the flexile and spinous rays can twine around and seize
other objects so as to perform directly the offices of prehension and
locomotion. The facility with which the Ophiura casts off a ray
which may be touched and even all the rays, leaving only its central
disc, when it is seized, is very surprising ; it is consequently very
difliicult to preserve specimens of this genus entire. To do this it is
recommended to plunge them suddenly into fresh water when they
instantly die in a state of the most rigid extension. I may state that
the Ophiura is one of the most ancient forms of animal life that
has yet been met with in the fossiliferous strata of our climate.
Professor Sedgwick has lately discovered it in one of the oldest
members of the Silurian system of rocks.

The mouth of the star-fish (Asferias) is situated at the middle of
the under surface of its body ; it is edentulous, and leads by a short
gullet into a large stomach, (Jig. 64. a), which sends off" a pair
of sacculated caecal appendages (b b) into each of the rays. The small
terminal pouches of these appendages appear to secrete a substance
subservient to chylification ; two or more small glandular sacs (c c) of a
yellowish colour open into the bottom of the stomach, and have been
regarded as a rudimental form of liver.

I 2

116 LECTURE X.

Caecal appendages are not continued from the central stomach
into the rays of the Ophiura or Comatula. In the latter genus the
alimentary canal presents a higher type of structure : there is a
slightly convoluted intestinal canal which terminates by a distinct
tubular anus.

Professor Tiedemann, in his celebrated monograph on the Echino-
derma, has successfully demonstrated the vascular system in all the
leading forms of that class. In the Asterias ruhens the vessels which
absorb the chyle from the digestive sac terminate, after a series of
reticulate anastomoses, in a circular trunk, which likewise receives
branches from the radiated caeca. The venous circle communicates
by means of a dilated tube, regarded as a rudimental form of
heart, with an arterial circle surrounding the mouth, from which
branches diverge to the rays and other parts of the body. I have
not been able to trace any direct communication between the true
vascular system of the Asterias and the system of canals, which, by
their connection with contractile divreticula, govern the supply of
fluid to the vesicles at the base of the hollow tentacles protruded
through the ambulacral pores. Tiedemann and Dr. Sharpey also
agree in rejecting the continuation of the erectile system of the feet
from the intestinal vascular system.

There is a small tube, called by Tiedemann the sand-canal ; its
position is indicated by the circular prominence or nucleus on the
dorsal aspect of the disc of the Asterias, near the angle between two
of the rays, which prominence resembles a miniature brain-stone
madrepore. The problematical calcareous column in question is con-
tinued from the nucleus into the interior of the body, and consists of
minute hexagonal plates, which are united into larger joints. From its
analogy with the jointed column of the crinoid star-fishes, it has been
suggested by Dr. Coldstream that it may be the analogue or rem-
nant of that column ; but, according to the observations of M. Sars,
the Asterias are not fixed animals in the young state. Dr. Sharpey has
conjectured that it may serve as a filter in the admission of sea water
to the tubular system of the ambulacral feet. Such a mechanism is
not, however, present in the Echini or Holothurice, which equallj'-
possess the systems of tubular feet.

As the sea water is freely admitted into the general cavity of the
body, and bathes all the viscera, their vascular surfaces thus stand
in the relation of a respiratory organ to the aerated medium, and
they are every where provided with vibratile cilia, which maintain the
currents of oxygenated fluid.*

The nervous system of the Asterias (p. \^, Jig. 4.) consists of a

* Sharpey, in Cyclopeedia of Anatomy and Physiology, art. Cilia.

ECHINODERMA. 117

slender chord surrounding the mouth (^), from which three delicate
filaments are sent off opposite the base of each ray : the middle one
is continued along the middle of the ambulacral groove, and swells,
according to Ehrenberg, into a small terminal ganglion, immediately
behind that bright coloured speck at the extremity of the ray which
the same acute observer regards as a rudimental organ of vision.

The organs of generation consist of groups of ramified tubes
(^fi9' 64'. d), arranged in pairs in each ray, and opening upon the
calcareous circle which surrounds the mouth. In the males these
sacculi are distended with a white fluid abounding in spermatozoa :
in the females they are laden with ova of a bright yellow or orange
colour, which distend the rays during the breeding season.

The five pairs of generative organs are restricted to the central
disc in the Ophiurce, which part in the breeding season is distended
with the milky fluid of the testis in the male, and with the round
yellow eggs in the female. They are discharged by orifices on the
ventral surface. In the Comatula the ovarian receptacles are much
more numerous, and are of smaller size : they occupy the inner side
of each of the pinnae or articulate processes sent ofi" from the rays.

Echinidce. The calcareous pieces entering into the composition of
the complex skeleton of the Echinus are those of the shell, of the
buccal apparatus called the " lantern," of the ambulacral tubes, and
of the pedicellariae.

All the Echini are admirable for the regular and beautiful pattern
in which, as in a tesselated pavement, the numerous calcareous pieces
composing their globular crust are arranged ; many of the species are
formidable from the size and form of the sjDines with which the shell
is beset. The component plates of the shell are divided into several
series, called oral, anal, genital, ocular, ambulacral, and interambulacral
plates. The proper shell, one half of which is exposed by removal
of the spines in figure 65, is built up of the two latter kinds, which
constitute a hollow spheroid, having a large aperture at each pole,

where the first four kinds of plates
are situated. The ambulacral
plates {a, fig, 65.) are perforated
for the passage of the tubular
feet, the parallel rows of which
^ intercept and overshadow spaces
compared by Linnaeus to avenues
or ambulacra; these plates like-
wise support spines. The inter-
ambulacral plates (z, fig. 65.'),
which support a greater number
I 3

118 LECTURE X.

of the spines, are characterised by more numerous tubercles, and
are not perforated. Both kinds of plates are of a pentagonal form,
and are arranged each kind in five alternate pairs of vertical
rows. The plates of each pair are united together by a zigzag suture,
and increase in size as they approach the equator of their living globe.
These twenty series of ambulacral and interambulacral plates con-
stitute the chief part of the spheroidal skeleton of the Echinus. The
large oral aperture is partly occupied by the small irregular oral
plates, which have no tubercles or spines, and are suspended in the
oral integument, from the middle of which project the points of the
five teeth. At the opposite aperture, immediately surrounding the
vent, are the small anal plates ; external to these are the five genital
or oviducal plates, so called because each is perforated by the duct of
an ovarium or testis ; the ocular plates are wedged into the external
interspaces of the genital plates, and are pierced near the apex by a
very minute pore, which lodges the ocellus and its little nerve.

One of the genital plates is larger than the rest, and bears a tubercle
corresponding with the nucleus or madreporiform tubercle on the
back of the star-fish. M. Agassiz, assuming this plate to be at the
back part of the Echinus, shewed that the other four genital plates
were in symmetrical pairs, and thus discovered the right and left sides
of the animal.

The calcareous constituent of the shell of the Echinus lividus, has
the following chemical composition, according to the analysis of
Professor Brunner, quoted by Professor Valentin.*

Carbonate of lime - 96*27
Sulphate of lime - 1*53
Carbonate of magnesia 0-93

100-00

The small anal plates are united together like the oral ones by an
extensile and contractile membrane. Both the internal and external
surface of the rest of the complicated shell is covered by a similar
organised membrane, which likewise extends through all the numerous
sutures of the shell. With this explanation of the general structure
of the crust of the Echinus we are in a condition to understand the
manner of its growth, which otherwise would be a difficult physiolo-
gical problem.

The Echinus maintains nearly the same spheroidal figure from its
earliest formation to full maturity ; and, notwithstanding that its soft

* Mur.ographies D'Echinodcrmes, d' Agassiz. No. I. 1841.

ECHINODERMA. 119

parts are almost entirely confined by a fragile and inflexible globular
crust, this is never shed and reproduced, like the shells of the crab
and lobster. At the same time the calcareous plates possess not more
power of inherent growth than the crusts of the Crustacea, which
they resemble in both physical and chemical properties. By the sub-
division of the hollow globe into many pieces, and the apposition of a
formative membrane to all their margins, addition is gradually made
to the circumference of each component plate, and by the plan of
their arrangement the spheroidal shell gradually expands, with little
change in its figure and relative proportions.

The amount of change in the form of the shell, which differs in
different species, depends upon the addition of new plates to the
ambulacral and interambulacral series. These are developed near
the oral and anal poles, but chiefly near the latter, where, in the
young CidariSi for example, the plates are more loosely connected
together, and support incomplete spines. In the membrane con-
necting such plates may be seen small irregular pieces, without tu-
bercles or spines, which grow by accretion to their margins, and then
have the tubercles developed upon their outer surface. The spines
are at first immoveable, and stand out like processes from the tuber-
cle ; the joint is not developed until after they have acquired a certain
size. The growth of the globe in the direction of its poles is chiefly
by the development of the new plates ; its expansion at the equator is
by the addition to the sutural margins of the old plates.

The spines of the Echini vary in form and relative size in different
genera ; their proximal extremity is adapted, by an excavation, to the
tubercles on the outer surface of the plate, to which it is attached by
a capsular ligament, and upon which it can be rotated by muscular
fibres external to the capsule. In the species of Cidaris, where the
spines are unusually large, an internal ligament extends from a little
pit upon the centre of the tubercle to the centre of the articular
cavity of the spine, analogous to the round ligament in the hip joint.
The spines grow by successive additions, through calcification of that
part of the common organised membranous covering of the shell of
the Echinus, which is attached to their base. The varied cellular
organisation of the spines, affords beautiful microscopical objects,
when viewed in thin transverse slices.

The tubes that issue from the ambulacral pores can be extended
beyond the longest spines in the Echinus Sphcera of our own coasts ;
they terminate in suckers, which appear to be highly sensitive, and by
which the Sea-urchin attaches itself to foreign bodies, and moves
along them with a rotatory course, in which the spines serve to
balance and direct the progress of the animal. The bases of the

I 4

120 LECTURE X.

tubes comnmnicate with the cavities of the internal vesicles or
branchiae. The terminal sucker of the tube is supported by a circle
of five or, sometimes, four reticulate calcareous plates, which intercept
a central foramen, and by a single delicate reticulated perforate
plate on the proximal side of the preceding group. The centre
of the suctorial disc is perforated by an aperture conducting to the
interior of the ambulacral tube.

I have reserved the notice of another class of appendages to the in-
tegument, not only of the Echini^ but of the Asterise, for this part of my
discourse, because they are most developed, most varied in structure,
and have been most minutely investigated in the species of the
globular family of Echinoderms. The appendages to which I allude
are called " Pedicellariae," and consist of a dilated end or head,
usually prehensile, supported by a slender stem or pedicel. They
present different forms, which hold constant and determinate positions
in the crust of the Echinus : they seem at no season to be absent, and
must therefore form part of the integral organisation of the Echino-
derm. They have however been conjectured by some naturalists to be
parasitic animals ; by others to be the young of the Echini, to which
they are attached.

In the Ech. lividus, Professor Valentin, to whom we owe the
most minute descriptions of these bodies, divides them into gemmi-
form, tridactyle, and snake-headed pedicellarise. They are all com-
posed of an internal calcareous axis, and a soft external tissue.

The gemmiform pedicellarise * are placed around the tubercles,
especially the largest ones ; their pedicel is long and slender ; their
capital resembles the bud of a flower, defended by three sepals, the
apex of each of which is produced inwards in the form of two pairs
of long and slender teeth. The quadridentate sepaloid plates can be
divaricated and approximated, and constitute a very effective pre-
hensile instrument : they are highly irritable; a needle introduced
into their grasp is instantly seized. The ciliated gemmule of any
parasitic coralline, which might settle about the base of a spine, and
there commence its growth, would be liable to be seized and uprooted
by the prehensile gemmiform pedicellariae, which are of microscopic
minuteness.

The tridactyle pedicellarise are of larger size, are visible to the naked
eye, and fit to grapple with and dislodge young sedentary parasites of
larger species, as Cirripeds and Conchifers. They are found more
particularly around the large tubercles of the interambulacral plates
which support the largest spines. Their capital is longer, narrower,

* Pedkellaria glohifera Muller.

ECHINODERMA.

121

and more pointed than in the gemmiform kind ; and the three pieces
are dentated and close upon each other, like the blades of pincers.

The " pedicellariae ophicephalae " are aggregated principally upon
the buccal membrane.

The pedicellarise of the star-fishes are diffused generally over the
surface, and form dense groups round the spines : they consist of a
slender contractile stem ; but the head resembles a forceps with two
blades : they are continually in motion, opening and shutting their
blades. They would wage as effective and serviceable a war in defence
of the integument of the Asterias against the attacks of the host of
parasites which the sea engenders, as their tridactyle analogues in the
Echini may do. In some species of Goniaster the pedicellariae resemble
the vane of an arrow, and are so numerous as to give a villous ap-
pearance to the integuments.

The muscular system of the Echinus, into the details of which the
limits of the present lecture forbid me to enter, includes the muscles
of the spines, those of the jaws or lantern, of the buccal membrane,
of the anus, of the ambulacral tubes, of the internal branchiae, and of
the pedicellariae. The muscles of the lantern and spines have their
ultimate filaments collected into primitive fibres or fascicles, which
are marked by transverse striae at regular distances as in the muscles
of insects. *

The digestive apparatus of the Echinus {Jig. 66.) consists of a

mouth armed with teeth, surrounded
by a muscular labial membrane, and
five pairs of pinnate tubular ten-
tacula, of an oesophagus and sto-
mach, and of an intestine suspended
by a mesentery to the interior of
the shell, and which, after perform-
ing a few circumgyrations, termi-
nates by a distinct outlet opposite
to the mouth. The outer margin
of the lip is fringed by a circle of
the ophicephalous pedicellariae, vi-
sible to the naked eye.

The teeth («) are five in number ;
they are calcareous, three sided
prisms, dense at the working apex,
softer at the base, with the inner
edge sharp and fit for cutting ; they are each implanted in a larger

o\l\',,u

Echinus.

Valentin, 1.

p. 101.

122 LECTURE X.

triangular pyramid (h), two sides of which are in close apposition
with opposite sides of the adjoining pyramids, and are transversely
grooved like a file, so as to operate upon the alimentary matters which
have been divided by the incisor plates, and which are thus minutely
comminuted before they pass into the membranous oesophagus.

The secretion of some simple salivary follicles assists in completing
the mastication of the food. These singular representatives of molar
and incisor teeth are moved upon each other ; and the entire pyra-
midal mass, which has been called Aristotle's lantern^ can be pro-
truded and retracted by certain muscles, w^hich have their fixed points
of attachment in five calcareous ridges and arches which project from
the inner surface of the plates near the margin of the oral vacancy of
the shell. For the particular description of these masticatory muscles,
which are classed under the following heads, 1. Musculi interarcuales,
s. comminutores ciborum, 2. Musculi arcuales, s. dilatores orificii den-
tium, 3. Musculi interpyramidales (sphincter oris), 4. Musculi trans-
versi, — I must refer to the Lemons d! Anatomie Comparee of Cuvier,
and the monograph of Professor Valentin, already cited.

The pharynx occupies the cavity of the lantern, and is divided by five
longitudinal folds, most prominent at their commencement ; the small
salivary caeca are placed close to its continuation with the oesophagus,
from which it is separated by a marked constriction. A slender oesopha-
gus (c) conducts to the gastric or caecal portion of the intestine (^); and
that canal twice performs the circuit of the abdominal cavity before
its final termination. The vent, its membrane, and the anal plates have
appropriate muscles for constriction and dilatation. The intestine is
generally found more or less loaded with fine sand ; its surface and
that of its mesentery is covered with a rich vascular network, which
conveys the nutrient fluid eliminated from the organic particles swal-
lowed with the sand, to a large vessel or vein, which accompanies the
intestine from the anus to the mouth, where it terminates in the vas-
cular circle around the oesophagus, from which the arteries are given
off for the supply of the whole body.

The sea water is admitted into the peritoneal cavity ; and its con-
stant renovation over the surface of the vascular membranes of the
Echinus, is provided for by the same mechanism of vibratile cilia as
in the Asterias.

There are external as w^ell as internal organs of respiration : the
former are the short, pyramidal, branched or pinnate hollow pro-
cesses, attached by pairs to the oral extremities of the interambulacral
areae, and consequently ten in number. Their outer surface is highly
vibratile.

The internal branchiae arc the transversely extended hollow bases of

ECHINODERMA, 123

the tubular feet ; which are covered with so rich a network of vessels
that Valentin compares them with the lungs of the Salamander.
The chief office of these sacs, according to Tiedemann, is to pro-
trude, by contracting upon their fluid contents, the tubular feet, con-
tinued from them through the ambulacral pores ; but as the ter-
minal sucker of these feet is unquestionably perforated, Valentin *
rejects this explanation; he thinks the tubular feet imbibe the sea
water by their terminal pore, and convey it to the internal basal sac,
for the oxygenation of the blood, circulating over its parietes.

The external branchiae are a more complicated form of respiratory
sac everted and extended ; they float in the external respiratory me-
dium, while the internal sacs receive it into their interior.

The sea water can be admitted into the interior of the visceral
cavity through the interspaces of the teeth ; if it be actually intro-
duced by the tubular feet it must pass by exosmose through the
pores of the basal sacculi, which is contrary to analogy.

Cuvier, Tiedemann, and Delia Chiaje have given more or less ac-
curate descriptions, but conflicting explanations, of the vascular system
of the Echinus.

There is no doubt that the fusiform dilated contractile vesicle,
situated near the oesophagus, and surrounded by a double fold of
the mesentery, is the central organ or heart. Its cavity is subdivided
by muscular walls. From its oral end a trunk proceeds, which forms
a circle around the CESophagus at the base of the lantern, from which
the vessels of that part proceed. A second trunk is continued from
the opposite end of the heart, in the opposite direction, and forms
a corresponding circle around the anus. A vessel called the intes-
tinal artery runs along the concave margin of the intestine ; another
trunk called the intestinal vein accompanies the outer or convex
contour of the intestine, and receives many branches from the
membrane of the shell. The vascular circle round the anus (e),
receiving the veins of the ovaria, sends off" five trunks which run
in the interspaces of the internal branchiae ; the capillaries of these
branchiae return into five other trunks, accompanying the preceding
five along the median interspace. One set must fulfil the office of
branchial arteries, the other that of branchial veins. The blood is of
a deep yellow colour; the blood-cells are granular and irregular,
but generally manifest a nucleus.

Prof. Valentin, after a minute and searching scrutiny into the
anatomy of the vascular system of the Echinus, is unable to deduce
from that alone the course of the circulation. The ascertained facts

* Valentin, p. 85.

124 LECTURE X.

will permit of two explanations. In the first and most probable mode
the heart transmits arterial blood to the artery proceeding to the
lantern and from its arterial ring to its soft parts, to the pharynx and
to the buccal membrane. From these parts the blood will return
into the venous ring of the lantern, and thence into the intestinal
vein, where, mingling with the venous blood from the intestine, it is
conveyed to the annular vessel of the rectum, which also receives the
venous blood of the ovaria. The blood thence passes into therfive
trunks which represent the branchial arteries. These distribute the
blood over the internal gills, or bases of the tubular feet, where it
acquires the arterial character. Thus changed the blood returns by
the branchial vein into the arterial ring of the anus, whence it is dis-
tributed in part to the ovaria, and the remainder by the intestinal
artery to regain the heart. In this view the vessel called by Tiede-
mann the intestinal artery performs the, office of a vein.

According to the second explanation, the heart transmits the
arterial blood by the intestinal artery to the oesophagus, intestine,
and rectum, and then supplies the ovaria, and perhaps also the
membrane of the shell. The venous blood collected into the in-
testinal vein is poured into the anal venous ring, which receives the
ovarian veins, and distributes the blood through the five branchial
veins : these will disperse it over the branchial sacs, where it will be
oxidized. Thus changed the blood returns by the branchial vessels
towards the auricles, and would be continued by their apertures
into the vessel of the internal oblique ligament, would then pass
along the pharynx, gain the arterial circle of the lantern, and re-enter
the heart by the vessel which passes from the lantern to it.

The nervous system consists in the EchinidcB^ as in the Asterias,
chiefly of a chord surrounding the pharynx, and of five trunks ex-
tending along the ambulacral interspaces. The pharyngeal ring is
an equilateral pentagon in the Echinus, and an oblong pentagon in
the Spatangus. In the Echinus it is situated close upon the inner
side of the apices of the calcareous pyramids which support the teeth ;
the ambulacral trunks are flattened, and may be distinguished from
the overlying branchial vessels by the connection of the latter with
the internal branchiae. Smaller nervous branches are sent ofi" from
each arch of the pentagon to the inter-pyramidal muscles and the
oesophagus. The ambulacral or branchial nerves diminish in size as
they proceed, supplying the internal branchiae and the ambulacral
tubes ; they finaUy terminate by penetrating the pore of the ocular
plate to gain the base of the red ocellus.

The generative apparatus of the Echinus consists of five mem-
branous sacs, the eff'erent ducts of which perforate five plates, sur-

ECHINODERMA. 125

rounding the anal plates, and thence called genital or ovarian plates.
This structure is common to both sexes, which are in distinct indi-
viduals in the Echini, as in the Star-fishes. The ovaria, when dis-
tended with the mature ova, which generally present a bright orange
colour, fill a great part of the cavity of the shell, and resemble the
ovaria or roe of fishes. They have at all periods constituted a
favourite article of food with the inhabitants of the Mediterranean
shores.

The ova consist of a vitelline membrane, vitellus, the transparent
germinal vesicle, and its simple nucleus.

The spermatic corpuscles are elongated, oval, rounded anteriorly,
pointed behind. They abound in the opake milky fluid, distending
the five secerning sacculi at the breeding season.

In the multiplicity of the pieces of which the shell of the Echinus
is formed, we may discern, by^the contrast which it presents with the
bivalve and univalve characters of the shells of the Mollusca, the same
low vegetative condition of an external skeleton which is exemplified
by the frequent repetition of similar parts in the multiplied mouths of
the Polypi, the multiplied stomachs of the Polygastria, and the mul-
tiplied ovaria in the Taeniae. If we view the articulated moveable
spines and the extensile and prehensile tubes in the light of primitive
forms of locomotive extremities, we shall see in their great numbers
and irrelative repetition, an illustration of the same law.

HolothuriidcB. The HolotJmria, the highest of the EcMnodermay
may be compared, as has been already observed, to an Echinus de-
prived of its spines, with its shell softened and elongated by diva-
rication of its poles. The coriaceous integument continues to be
perforated by innumerable apertures^ which give passage to tubular
i^iiX, of precisely the same structure as those in the sea-urchins and
star-fishes. These tentacles are likewise in some species of Holothurice
disposed in five longitudinal ambulacral series ; in a few species
(Psolus Oken) they are confined to a sort of ventral disc : in other
species the suckers are generally diffused over the integument. The
only calcareous substances in this coriaceous integument consist of
a circle of osseous pieces, which partly defend the nervous ring, and
which afford a firm attachment to the branched retractile tentacles
which surround the mouth. These tentacula may be likened to a
more complicated form of the ordinary tubuli of the body, each
being connected at its base with a long hollow sacculus, and being
distended and protruded by the injection of the fluid contained in that
sacculus.

The alimentary canal is closely analogous to that of the Echinus ;
but its disposition is accommodated to the vermiform character of

126 LECTURE X.

the Holothuria : its anal termination dilates into a cloaca, from which
two long ramified caeca are continued ; but these admit only sea
w^ater from the cloaca. The alimentary canal in the Sipmiculus*
differs from that in the Holothuria in being reflected from the pos-
terior extremity of the body to terminate near the anterior end,
without dilating into a cloaca, and without the development of any
anal caeca. The intestine is longer and more convoluted in its course.

The Sipiincuhts is a marine vermiform animal w^hich burrows in sand,
and, although it has no tegumentary tubular feet nor organs of re-
spiration, is most closely allied to the Holothuria^ and is therefore
retained in the class Echinoderma, in w^hich it makes the nearest
approach to the true Vermes. The anterior position of the vent in the
Sipunculus precludes the necessity of the worm quitting the retreat,
which its safety demands on account of its integument being less
thick and coriaceous than in the Holothuria.

The rich vascular system of the Holothuria is most conspicuous
upon the intestine and mesentery, and has been beautifully illustrated
by the injections and drawings of Hunter.f Here, however, we
find the intestinal vessels carrying the nutrient fluid to those cloacal
caeca which are transformed into a distinct respiratory organ, and
which presents the form of two long and beautifully arborescent
tubes.

The complex circulating system in the Holothuria is in great part
represented in this diagram in connection with the equally extensive
system of sinuses and canals which regulate the protrusion and re-
traction of the numerous tubular feet.

The ampulla Poliana {Jig. 67. a), w^hich is double in some species,
is the analogue of the blind sacculi, which supply the canal of the
bases of the feet in the Asterias, but is called the heart by Delia
Chiaje. It transmits its fluid principally to an annular reservoir
round the pharynx (6), whence proceed the canals of the oral ten-
tacula (c) and those supplying the tubes which perforate the coriaceous
integument. The latter canals (c?, d) run down in the interspaces of
the pairs of muscles, and distribute transverse branches to the bases
of the tubes as they proceed. The most important part of the un-
equivocal circulating system is the trunk (e), which runs along the
free border of the intestine, and which is characterised by the short
and wide anastomotic trunk (/, /) analogous to the heart in the
Echinus, and which connects the corresponding vessels of the two
principal folds of the intestine. The intestinal capillaries reunite^

* Prep. No. 438. A.

f See Preps. Nos. 437, 438. 984.

ECHINODERMA.

127

performing at the
same time the of-
fice of absorbents
and conveying the
chyle to the great
intestinal vein (^),
from which pro-
ceed the singular
and beautiful re-
spiratory plexuses
(h, h), which are
submitted to the
influence of the sea
water by contact
with the branchial
trees.

The aerated blood
is conveyed to a
great mesenteric
trunk (i, i), or
branchial vein,
from which it is
transmitted to the
parietes of the
body, and returns
by the cloaca to
form the intestinal
artery.

Hunter has fi-
gured certain glan-
dular sacs opening
into the stem of
the hollow branch-
iae, which may be
regarded as a ru-
dimental form of
an excretory or
renal system.
The chief divisions of the nervous system consist of the pharyngeal
ring, which is closely applied against the inner side of the calcareous
circle, and of the flattened chords which proceed along the groove
or middle interspace in each of the pairs of longitudinal muscles, which
traverse the interior of the integument of the animal through its entire

128 LECTURE X.

length. The integument is also acted upon by transverse fibres
which run external to the longitudinal bands ; and such is the irrita-
bility of this muscular system, that when the Holothuria is disturbed
or captured it will sometimes eject its sand-laden intestine and most
of the other viscera by the cloacal aperture, and very effectually unfit
itself for anatomical investigations.

The generative organs constitute, as in other Echinoderms, a very
considerable part of the abdominal viscera in the breeding season ; but
they present a more complicated form : they consist of a branched sys-
tem of long and slender caecal tubes {Jig. 67. r), opening externally by
a single common canal, whose orifice is near the mouth. The gene-
rative organ of the male Holothuria resembles that of the female in
structure ; but the sexes may be readily recognised at the breeding
season by the different character of the contents of the tubes^ which
are white or colourless in the male, whilst the ova present a reddish
or yellowish hue.

The generative organs of the Sipunculus are two straight, slender,
unbranched, blind tubes, symmetrically disposed, and terminating each
by a distinct orifice at the anterior third of the body.

Among the few observations which have hitherto been recorded
of the development of the Echinoderms, are some which are of great
interest.

According to M. Sars, the star-fish, immediately after exclusion
from the egg, presents a depressed, round form, with four short club-
shaped appendages at the anterior extremity ; the young animal moves
by vibratile cilia with the four arms in advance : at the end of twelve
days the five rays begin to grow, and in eight days more the hollow
feet appear. The swimming motions have now ceased altogether ;
the four original ciliated arms shrink, and in a month they have en-
tirely disappeared, and the animal exchanges its binary for the
radiated figure.

The ova of the Comatulse escape from each receptacle, through a
round aperture, about the month of July, adhering together in a
roundish cluster of about one hundred. About the time of the
dispersion of these ova, the minute Pentacrini appear, attached to
the stems and branches of corallines, and occasionally to sea-weed.
This is attached by a convex calcareous plate, from the centre of
which arises the column composed of about twenty-four joints. The
capital of the column or body bears five bifurcating arms, which are
at first simple, but afterwards acquire the pinnae, and subsequently
the dorsal cirri. They further resemble small Comatulae in having
a separate mouth and lateral prominent vent. These small Pen-
tacrini attain the height of about three-fourths of an inch.

ANELLATA. 129

The small Pentacrini entirely disappear in September, at which
season the young Comatulae make their appearance. It is the opinion
of Mr. Thompson, the discoverer of the Pentacrinus Europceus, that
this pedunculated star-fish is a transitional state of the young Comatula,
an opinion which is adopted by Mr. Thompson, Mr. Ball, and Mr. Forbes,
experienced naturalists, who have each obtained and compared the Pen-
tacrini and young Comatulae. The actual metamorphosis of the Pen-
tacrinus into the Comatula has not yet been seen : we must suppose
that it enters life at first in the active stage of a ciliated gemmule ; that
it next selects the appropriate situation for its sedentary pentacrinite
stage of existence, and, finally dropping from the stalk, by an act of
transverse fission, a second time assumes a free condition of existence
under its mature form. Nor are these metamorphoses a whit more ex-
traordinary than those of the gelatinous Medusae : nay, the parallel
would be extremely close, since we saw that the Cyancea entered life
as a ciliated locomotive infusory, then became a sedentary polype,
supported on a central stem, which, finally, resolved itself into the
freely swimming Acalephans by several transverse fissions.

Other highly interesting considerations arise out of the pre-
dominance of the Pentacrinite forms over the Asteriae or Echini, in
the limestones of the ancient transition epoch in Geology. As we
advance in our survey of the organisation and metamorphoses of
animals, we shall meet with many examples, in which the embryonic
forms and conditions of structure of existing species have, at former
periods, been persistent and common, and represented by mature and
p recreative species, sometimes upon a gigantic scale.

LECTUEE XL

ANELLATA.

In both the Infusorial and Entozoic classes the body assumes a
more perfect linear and bilateral form as the species advance in the
scale of organisation ; and we have seen in the subjects of the pre-
ceding discourse, that even the typical radiated class of the zoophytic
sub-kingdom conducts by the Holothurian and Sipuncular families to
the vermiform type of the articulated sub-kingdom, in which the ve-
getative principle of development, by the frequent repetition of
similar parts, is still conspicuously manifested, but exercises its

K

130 LECTURE XI.

energies in a linf^ai" direction, and forms successive segments from
before backwards. We find, in fact, at the lowest step of the great
Homogangliate series of the Animal Kingdom an extensive group of
vermiform animals, some of which very closely resemble the Trema-
tode, and others the Nematoid, Entozoa, and all are devoid of jointed
limbs : but they possess a distinct circulating system of arteries and
veins, and in almost all the species the blood is red. They have
therefore been called " red-blooded worms," " vers a sang rouge,"
and " anellides," by the French naturalists ; in Latin A?iellata, from
anellus, a little ring, because the entire body of these worms is made
up of a succession of segments like little rings.

The mind is not easily liberated from the sway of opinions that
have long been held as authoritative ; although Cuvier seems to have
been the first to detect the exaggerated importance of the zoological
character derived by Aristotle from the colour of the blood, yet the
judgment of the great modern reformer of zoology continued to be
so far biassed by that character, that in his latest edition of the
** Regne Animal," he continued to place the Anellides, on account of
the colour of their circulating fluid, at the head of the articulate
series, above the Crustaceans, above the Arachnidans, above the
Insects, whose transitory larval condition these apodal worms seem
permanently to represent.

The body of an Anellide is always very long, soft, and subdivided
into a number of segments, for the most part closely resembling or
identical with each other. In many species the first segment is so
slightly modified as scarcely to deserve the name of head ; in others
it is the seat of higher senses and more varied functions, and is at
once recognisable as the cephalic segment.

In the lowest forms of the Anellata the locomotive instruments
are suctorial discs, as in the Trematode worms ; but the suckers
are always two in number, and are terminal in position. The species

next in order have stiff hairs or mi-
nute hooks projecting from each seg-
ment. In most Anellides there is on
each side of the body a long row of
tufts of bristles, supported upon fleshy
tubercles, which indicate the rudi-
ments of lateral and symmetrical lo-
comotive members, (^fig- 68.) There
are often two such organs, placed one
(«) above the other (^), on each side
Aphrodita. of the Segments of the body. In some

species the two setigerous tubercles

ANELLATA. 131

are confluent, and in almost all there exists at the base of each a
long soft cylindrical appendage called the "cirrus (c)." The bristles
in the setigerous Anellides are their chief organs of locomotion, and
at the same time their weapons of attack and defence. They are
generally sharp, or barbed, and hard enough to readily penetrate the
soft bodies against which they strike.

The nervous system of the Anellides presents a marked advance
beyond its condition in the white-blooded parasitic worms ; it con-
sists of a double median central chord or chain of small ganglions, ex-
tending from one end ot the body to the other ; the two chords diverge
anteriorly to allow the passage of the oesophagus, and again unite
above that tube to form a distinct, though small, bilobed cephalic
ganglion.

Most of the Anellides are provided with ocelli, and in many of
them the head supports soft cylindrical tentacules called "antennae :"
they are obviously organs of touch, but diiFer from the antennae of
insects in the absence of joints. In the first appearance of these not
yet well understood organs of sensation, which form so remarkable
and conspicuous a character, and so important an endowment of the
higher articulate classes, we have again an interesting illustration of
the principle of vegetative repetition ; for every setigerous tubercle
in the Anellides with cephalic antennae, has a similar organ of sen-
sation : the distinction is merely local and nominal ; the feelers on
the first segment being called "antennae;" those on the other seg-
ments " cirri."

The mouth is at the lower surface of the head, or at the anterior
extremity of the body in the acephalous Anellides ; in some species
it is provided with a protractile proboscis, and with lateral jaws in
the form of curved dentated horny plates ; and the alimentary canal is
generally straight, and in some species simple ; in others, pro voided
with a greater or less number of lateral caeeums. The anus is
situated above, or at the posterior extremity of, the body, and the
degree of redness of the circulating fluid varies considerably ; in
some species it is very pale : in one or two it even presents a greenish
hue : it circulates in a closed and very complicated system of vessels,
of which the chief dorsal one is distinguished by its undulatory pul-
sations ; and in some species the circulation is further aided by
contractile sinuses, called hearts.

All Anellides have organs of respiration, adapted in a few species
for extracting oxygen directly from the atmosphere ; and in the
rest of the class through the medium of water : in these the gills
are usually external, and vary considerably in form and position.

Such are the general anatomical characters of the class Anellata^

K 2

132 LECTURE XT.

and such the progress each system of organs has made in the transit
from the Nematoneurous to the Homogangliate types. The Anellides
are distributed into orders, according to obvious and easily re-
cognisable modifications of the locomotive and respiratory organs ;
which characters fortunately coincide with the general conditions and
grades of their organisation, and are therefore natural ones. Dr.
Milne Edwards, the pupil of Cuvier who has devoted most attention
to the Vermes thus grouped together by his great master, divides
them into four orders.

The first is the Anellata suctoria, and comprises the leeches,
which are provided with a suctorial disc at each extremity of the
bod}', and have neither bristles nor tuberculate feet.

The second order is the Anellata terricola, which includes the
earth-worms ; these have neither tubercular feet, nor external gills,
nor suckers, but are provided with short stiff" bristles fulfilling the
function of feet.

The third order is the Anellata tnhicola, and includes all those
which are provided with setigerous feet and have the respiratory
organs at the anterior extremity of the body. The Anellides of
this and the two preceding orders can scarcely be said to have a
distinct head.

The highest organised Anellides are also the most locomotive :
they have been called Errantes by Dr. Edwards. In them, the
respiratory organs are most developed, and from their position,
Cuvier, who first defined the order, has denominated it Dorsi-
hranchiata, the gills being attached to the sides of the body on the
dorsal aspect, along the middle part, or through the whole length of
the body. They are provided with setigerous processes for loco-
motion, and have always a distinct head. They are commonly known
by the name of Sea-centipedes, Sea-mice, or Nereids, from the
Linnasan generic name Nereis, which is almost equivalent to the
present ordinal term, Errantes.

The tubular sheaths and protractile bundles of bristles which
constitute the organs of locomotion in this order have been already
noticed in the general characters of the class. The integument is
naked, soft, vascular, and highly susceptible of impressions in all the
Anellides. It is sometimes red, sometimes the epidermis reflects
iridescent tints. In the tubicular order the habitations are commonly
formed of foreign substances, as particles of sand or shells agglutinated
together by the mucous secretions of the worm, which is sometimes
done v/ith a considerable degree of neatness and apparent skill, as in
the PectinaricB and Terebellce. The Serpula secretes a calcareous
tubular shell, consisting of carbonate of lime and animal matter, like

ANELLATA.

133

Leech.

the shells of Mollusca ; but differing in being quite external to the
integument, and not organically attached to the animal, which can
quit and return to its tube. Most species of Serpulis, as the Serjy.
contortuplicata, which coats the shells of oysters and other bivalves
with its characteristic dwelling, have a pedunculated operculum for
closing the entry of the tube.

The organisation of the integument has been studied chiefly in the
naked Anellides. It consists, in the leech, of a strong, smooth
whitish epithelium, and of a cellular corium divided into short segments,
and having many pigmental cells of a brown or greenish colour,
except in the intervals of the rings. The muscular fibres have a
tendinous lustre : those of the outer layer are transverse ; those of
the next layer cross each other
diagonally, and form a fine re-
gular reticulation : beneath these
are the longitudinal fasciculi,
which form the most conspicu-
ous stratum. There are also
other smaller muscular fascic-
uli in the under surface of the
body, besides those which spe-
cially regulate the action of the

terminal suckers and the dentated jaws (^Jig- 69. h).
The mouth of the leech (^fig^ 69.) is triangular, and
is armed with three crescentic jaws (a, a), presenting
their sharp convex margin towards the oral cavity,
which margin is beset with sixty small teeth (^fig.
70.). It is by the action of these
little saws upon the tense integument
seized by the labiaF sucker, that the
characteristic triradiate bite of the
leech is made.

The oesophagus (^fig. 71. ^) is short,
and terminates in a singularly com-
plicated stomach, divided by deep
constrictions into eleven compart-
ments, the sides of which are produced into caecal
processes (c, c\ progressively, though slightly, in-
creasing in length to the tenth, and disproportion-
ll \W-d ^^^^y elongated in the eleventh, compartment. The

l! 1| first gastric chamber is the smallest. In the eight

posterior compartments the anterior part of each
slightly expands to form a pair of small accessory
K 3

Jaw and teeth.
Leech .

Leech.

134 LECTURE XI.

caeca. The middle part of the eleventh division extends backwards,
in the form of a small funnel-shaped process, and opens into the
commencement of the slender intestinal canal (f/, d) ; this is situated
between the two last and longest gastric caeca (^c) ; it terminates by a
small anus (e) above the terminal sucker.*

There is a whitish glandular stratum in the coats of the oesophagus,
representing the salivary system. A peculiar brown tissue extends
along the alimentary canal between the nervous chord and the mucous
glands, and also upon the dorsal aspect of the anterior part of the
cavity. It is composed of a congeries of elongated, convoluted, and
irregularly constricted follicles, which are united in groups by the
confluence of their ducts into a single slender excretory tube. These
tubes unite with those of other groups of the follicles, and pour a
secretion, analogous to bile, into the posterior divisions of the stomach
and into the intestine. The confluence of the hepatic ducts is very
remarkable and conspicuous when they lie upon the testes, f

The mouth is furnished in the earth-worm with a short proboscis,
but is without teeth : the decaying parts of animals and vegetables
are swallowed with the soil, and conveyed by a short and wide oeso-
phagus to a muscular compartment of the digestive canal, analogous
to a gizzard. The oesophagus is sometimes dilated, like a crop, above
this part. The long and wide intestine is continued straight to the
terminal vent, and is constricted in its course by the transverse septa
of the common cavity of the body ; but the sacculi are not produced
into caeca.:}: It contains along and slender blind tube, called the
typhlosole, attached to the inner surface, in which the chyle is strained
off" from the coarse contents of the wider intestine.

The obliquity of the constrictions of the alimentary canal in the
Sabella pavoniiia § give it the appearance of being a long and narrow
tube disposed in a series of close spiral coils ; but it is merely saccu-
lated. In most other tubicolar anellides the intestine is less constricted
than in the Sabella.

In the TerehellcB nebulosa and conchilega the wide oesophagus is
separated from the slightly sacculated gastro-intestinal tube by a con-
striction, which lodges an annular vessel. In the Hermella there is a
short oval dilatation or stomach between the oesophagus and intestine.

In the sand -worm (Are?iicola) the gastro-intestinal canal (Jig- 73.)
commences at the termination of the oesophagus (b) by a sudden
dilatation, into which two caecal glandular pouches (c) pour their
secretion : the rest of the canal is simple in its outward form ; but

* See Preps. Nos. 442. 466, 467, 468, 569. 595. A.

f Brandt, Medizin Zoologic, Bd. ii.

i Prep. No. 595. B. § No. 441 .

ANELLATA. 135

its walls are thickened by a stratum of minute secerning cells (d),
which prepare a greenish -yellow fluid.

The alimentary canal commences in many of the Nereids by a pro-
boscis formed by a loose and muscular cylinder, which can be in-
verted and protruded like the finger of a glove ; its extremity in some
species is encircled by smal papillae; in some it supports a rasp -like
horny plate ; in others it is armed by one or more pairs of lateral
horny dentated jaws.

In most of the Nereids there is no distinction between stomach and
intestine ; in some species the canal is provided with lateral pouches.
In the Aphrodita aculeata the part analogous to the projectile pro-
boscis of the Nereids is converted into a kind of gizzard, by the
thickening of the muscular coat. The alimentary canal, continued
from its posterior extremity, bends forward at first for half the length
of the gizzard, a disposition which indicates the occasional protrusion
of this part. The canal then bends backwards, and is continued
straight to the anus. Through the whole length of the intestine,
caecal processes are sent off on each side, to the number of about
twenty pairs. They commence of a slender diameter, but gradually
enlarge, send off" many short branches, which subdivide, and terminate
in fusiform csecal pouches. These productions of the intestinal canal
seem obviously analogous to the gastric caeca of the leech ; but they
are more isolated from the common canal^ and more distinct in their
functions. It is thought that the chyme passes into them, and that
the chyle is separated from it by a secretion of the terminal caeca
analogous to bile. Hunter has placed this preparation * at the
commencement of his series of hepatic organs, as one of the early
forms of that system.

In the majority of the Anellides the blood is red ; in some of a
brilliant red, as in the Arenicola, Nereides, Glycera, Nephtys. In the
Aphrodita acideata and in the Polynoe, the blood is of a pale yellow
colour ; in a species of Sahella it is olive green ; so that, as Milne
Edwards well observes, the colour of the blood is far from being a
character of such physiological importance as to justify the location
of the Anellides at the head of the articulate sub-kingdom. In all
the species the blood is characterised by granulated circular cor-
puscles, of very variable dimensions, in the same animal. It circulates
in a closed system of arteries and veins, the modifications of which
are considerable when examined in the different genera of the
class.

A large vessel which rests on the digestive tube, is the seat of

* No. 782.
K 4

136

LECTURE XI.

undulating contractions, by which the blood is propelled from behind
forwards ; it fulfils the functions of the heart, and is very obviously
the analogue of the dorsal vasiform heart in insects. A corre-
sponding venous trunk conveys the blood in an opposite direction
from the head to the tail, along the under or ventral surface of the
abdominal cavity. The circulation is often aided by the contractile
walls of partial dilatations of certain of the vessels, and by the actions
of the gills themselves in the higher anellides.

In the leech the vascular system consists principally of four great
trunks, none of which present any local dilatations meriting the name
of heart ; one of these trunks is situated on each side, a third above,
and a fourth below, the alimentary canal. They are shown in trans-
verse section, as connected together in two of the middle segments of
the leech in this diagram, from Brandt's Monograph {Jig. 72.) The la-
teral trunks (c, c) are the
largest ; they are widest
in the posterior third of
the body ; their anterior
end terminates in branches
to the head ; the posterior
end unites with that of
its fellow more conspic-
uously than at the an-
terior part, and supplies
the terminal sucker.
Branches are given off
at each ring, which almost immediately divide into a dorsal {d) and
ventral (e) ramulus ; the six posterior dorsal branches unite with
those of the opposite side, and the six arches thus formed are joined
together by two nearly parallel longitudinal vessels near the middle
line of the back.

The dorsal vessel {fig. 72. a), in which the blood moves from be-
hind forwards, is formed by the union of the dorso-intestinal vein and
of the dorso-dermal vessel, which run parallel with each other along
the posterior third of the body. The trunk is thence continued for-
wards, sending outwards a pair of transverse branches at each ring,
and bifurcating behind the mouth to enclose the oesophagus. From
the under part of the oesophageal ring the great ventral vein {fig.
72. h) begins, which is continued along the nervous ganglionic chord,
and swells at each ganglion, forming a sinus around it ; the nervous
matter being thus, as it were, bathed in the nutrient fluid. * From

Leech.

* Johnson On the Medicinal Leech, Svo. 1816. p. 114.

ANELLATA. 137

each of these swellings a transverse branch is sent off to either
side (/,/), and from the seventh to the fifteenth ganglionic sinus a
second pair of transverse vessels of smaller size is given off, just be-
hind the ganglionic sinus.

The respiratory function would seem to devolve partly upon the
tegumentary capillaries, and partly upon those capillaries which spread
upon the mucous sacculi. These latter capillaries are not, however,
more numerous than those of the other organs of the body. The
more important office of the, sacculi would seem to. be as the
recipients of the secretion of peculiar loop-shaped glands, which
they receive by a very short and slender duct. There are seventeen
pairs of these mucous glands (^figs. 71, 72. g^ ^), the five posterior of
which lie on each side the long terminal gastric sacculi, and the rest
in the interspaces of the shorter caeca. Each gland pours its se-
cretion into a circular sac {Jigs.l\,12.h,K)y which opens exter-
nally {^fig.ll. i, i) upon the skin. These dermal pouches have com-
monly been described as the respiratory organs ; they are evidently
analogous in their position to the respiratory organ of the higher
Articulata ; but in function they seem to be reduced to supplying
the skin with its abundant mucous secretion, and the ova with their
cocoon-like coverings at the season of generation.

Morren has minutely described the circulating system of the earth-
worm ; in a species of which {Liimbricus variegatus) Bonnet * saw
the red blood propelled forward by the systole and diastole of the
dorsal vessel towards the head, and noticed its accelerated course near
that part.

In the tubicolar anellides, according to Dr. M. Edwards f, the dorsal
contractile artery is unusually short. In the Terehella it receives nu-
merous veins from the intestine, and a large accession of the circu-
lating fluid from two wide transverse venous trunks, which encircle
the commencement of the intestine, and which receive recurrent veins
from the oesophagus, also a small vein from the integuments of the
back. This short dorsal vessel is, in fact, the general receptacle of
the venous system, and, by its function, it represents a pulmonic
heart. It transmits the venous blood almost exclusively to the ce-
phalic branchiae by three pairs of branchial arteries, which arise from
its anterior extremity. The oxygenated blood is returned by the
branchial veins to a large ventral trunk, situated immediately above
the ganglionic nervous chord. This vessel supplies a pair of trans-
verse branches to each ring of the body, which distribute filaments
to the integuments and the feet, and then ascends to supply the intes-

* Observations sur les Vers, (Euvres, i. p. 121.

t Sur la Circulation dans les Anellides, Annales des Sciences, Nat. X. p. 193.

138 LECTURE XI.

tine, where, with the absorbent veins of that canal, it returns again
into the dorsal vessel. In some other species of Terebella, as the
Ter. conchilega, the lateral branches of the ventral trunk do not
ascend in loops upon the upper surface of the intestine, but terminate
almost exclusively in a vascular network situated on each side of the
abdominal cavity near the base of the feet. The principal organs of
impulsion of the circulating fluid in the tubicolar anellides seem
to be the contractile branchiae, which thus combine, as it were, the
functions of both heart and lungs.

Cuvier has noticed the alternate expansion of the branchiae of the
Areyiicola when they are coloured by the bright red blood, and their
contraction, when, by expelling the blood to the internal vessels, they
become of a pale grey colour.

In the Eunice sanguinea * there is, as in the Terebella, a large and
short dorsal vessel, which rests upon the pharyngeal part of the ali-
mentary tube, and which communicates, by its posterior extremity,
with a vascular ring surrounding the commencement of the intestine.
This ring receives two vessels, which run parallel and close together
along the dorsal aspect of the'intestinal canal, and correspond with the
single vessel in the Terebella, The dorso-pharyngeal contractile
trunk receives other branches from the parietes of the digestive tube,
and a small medio-dorsal cutaneous vessel. It gives off by its anterior
extremity several branches to the head, and others which surround
the pharynx, and anastomose with the ventral vessel. From this
vessel a pair of lateral branches is given off at each ring of the body.
These branches immediately dilate, and are bent upon themselves in a
strong sigmoidal curve, appearing at first sight to be simple oval
vesicles. They send an ascending branch to the digestive tube, form
a small plexus at the base of each of the feet, and penetrate the
branchial filaments. The blood is returned from these respiratory
organs by transverse veins, which terminate on each side in the dorso-
intestinal vessel of that side. Here therefore the respiratory circula-
tion is removed further from the dorso-pharyngeal heart, which^ con-
sequently receives a greater quantity of blood in its arterial or
oxygenated state. The principal dynamical organs are, however, the
curved dilated sinuses at the bases of the branchiae, which pulsate
with strong contractions, and propel the blood at once to the branchiae,
the feet, the skin, and the intestine. If we call these pulsatile re-
servoirs by the name which their functions would claim for them,
there will be several hundred hearts in one of these gigantic Nereids.

In the Amphinome capillata, which Hunter has here f dissected for

* Edwards, loc. cit. p. 204. f Preps. Nos. 875. 889.

ANELLATA.

139

73

the vascular system, this is chiefly remarkable for the size and com-
plexity of the branchial plexuses.

In the Are7iicola {fig. 73.) there is, on each side the base of the
oesophagus, an ovoid contractile sac (/), which
sends off a large and short vascular trunk down-
wards and backwards to the medio-ventral line,
where, uniting with its fellow trunk, a ventral
vessel (e), analogous to that in the Eunice and
Terehella, is formed. This median vessel fur-
nishes a pair of transverse branches to each
ring, which at the seventh segment begin to
penetrate the ramified branchia, attached to
the sides of that and succeeding middle seg-
ments of the body. The pulsations of the
two oesophageal sinuses, or ventricles, propel
the blood into the ventral vessel from before
backward through these vessels (m, m) to the
gills, where it receives a new impulse by the
contractions of these organs, and, after having
been oxygenised, it is returned, partly by cu-
taneous vessels, which form many anastomoses,
and chiefly by a direct and continuous lateral
vessel (kj k) to the medio-dorsal intestinal
artery {g). This artery extends from one end
of the body to the other. At its middle part
it receives many transverse branches from the
digestive tube, and through them anastomoses
with the inferior intestinal vein (h). The vas-
cular network thus formed around the in-
testine, gives origin anteriorly to two lateral
veins (i), which terminate in the dorsal vessel
immediately behind the oesophageal ventricles.
The blood from the inferior intestinal vein is
conveyed to the same point or sinus. After
the communication of this common sinus with
the two hearts, a slender median vessel {g'), a continuation of the
dorsal one, extends forwards towards the head, and terminates
by forming two vascular rings around the base of the proboscis^
from the lower part of which the ventral vessel arises, which
vessel (e), passing backwards, receives the great accession of blood
from the two contractile hearts, and thus the circulation is com-
pleted.

Arenicola.

140 LECTURE XI.

This has much analogy with the circulation of the blood in the
earth-worm, in which the blood travels from behind forwards in the
dorsal vessel, and descends in great part towards the ventral vascular
system through the pairs of anterior beaded contractile sinuses or
hearts *, which differ only from the two ventricles in the Arenicola
by their greater number. In the lateral vascular canal, which ex-
tends along the anterior part of the body, at the base of the feet in
the Arenicola, and which is formed by the anastomoses of one of the
branches of the cutaneous arteries, we have the analogues of the
lateral vessels in the leech tribe, which are wanting in most of the
higher Anellides. The dorsal and ventral trunks are common to all.

The most striking physiological character of the circulation in the
Anellides as a class, is the continuity of their capillary system, and the
difficulty of determining which is the arterial, and which the venous
trunk of any one of the organs or parts of the body, excepting the
branchiae. There alone, we find that the blood received from the
distinct artery is sent back by as distinct a vein, which returns along
the same route as the artery, as it does in the limbs of the higher
animals. By the rapid division and general system of anastomoses
of the arteries and veins, it follows that almost all the parts of the
body are supplied by a mixture of arterial and venous blood.

The position and general relations of the branchial organs have
already been incidentally pointed out ; and it seems only necessary
here to allude to their different forms. In the leech and earth-worm,
a series of pores or stigmata on each side of the body lead to as
many simple sacculi (^Jig.ll. h,h), formed by an inward folding of
the integument. Carry the duplicature further in, divide and subdivide
tij and ramifications of air tubes, like the tracheal respiratory system
of insects, would be produced. We may perceive in the lateral air
sacs of the leech and earth-worm, the first step in the development of
the very peculiar air-breathing organs of the higher Articulata. The
air sacs of the abranchiate anellides, in their actual rudimentary
form, have their respiratory functions reduced to the lowest state,
and serve chiefly the office of excretory organs, preparing and
discharging mucus.

The respiratory organs of the Tubicolar anellides are in the form
of long, and sometimes tortuous, filaments f which radiate from the
head, generally in two lateral fasciculi. When not coloured by the
red circulating fluid, they are often barred and variegated by bright
purple, green, and yellow tints, forming a rich and gorgeous or-
namental crown.

* See Preps. 876, 877, 878. t Prep. No. 990.

ANELLATA.

141

The branchiae of the Anellata errantia * are usually in the form of
shorter tufts than the cephalic ones of the Tubicola ; and they are
attached to the upper part of the sides of a greater or less number of
segments. In some species, as the Nereis lamelligera^ the branchia is
formed by a flattened vesicle, including the ramifications of the
branchial vessels, and attached to the base of the upper tubular foot.
We shall afterwards see the homologue of this respiratory plate
taking an important share in the locomotive functions in the higher
organised forms of Articulata.

LECTUEE XII.

ANELLATA.

Hitherto the highest condition of the nervous system which we
have observed has been that of detached ungang-
lionic filaments diverging from a single sub-oeso-
phageal ganglion or from a simple oesophageal ring,
continued unconnectedly along the abdomen, or
diverging in rays down equidistant tracts of the
common parietes of the body. If we have met with
ganglionic masses in connection with coloured ocelli,
these have been as in the Acalephae, either so situated
as to give no indication of a head, or so multiiDJied
as to lose all significance as a common cerebral
centre of sensation.

In the class Anellata the nervous system has
reached a higher type and more constant plan of
arrangement. It always commences by a symme-
trical bilobed ganglion, which, both by its situation
above the mouth, and by the parts which it sup-
plies, merits the name of brain, which it has com-
monly received.

In the medicinal leech there are sent off from this
ganglionic centre {fg. 74. a) ten distinct optic
nerves (bb\ besides many smaller filaments to the
integument and other parts of the head : each optic
nerve or filament terminates by expanding upon the
base of a black eye-speck or ocellus, ten of which
you will easily distinguish by the aid of a moderate
magnifying power, dotting at equal distances the
upper margin of the expanded suctorial lip.

"^ Preps. Nos. 987, 988, 989.

142 LECTURE XII.

The principal nervous productions of the brain of the leech are
what may be termed its crura, which diverge as they descend to
embrace the oesophagus, and are called the oesophageal chords ;
they then converge and reunite to join the large cordiform sub-
cesophageal ganglion (c). From this ganglion the muscles of the
three serrated jaws, as well as the principal muscles of the oral
sucker, derive their nervous influence. Those who have watched
the vigorous workings of this part in a hungry leech, beginning its
parasitic feast, will not be surprised at the great development of the
nervous centre of the suctorial and maxillary mechanism. Two
chords, in such close apposition as to seem a single nervous band,
are continued from the suboesophageal ganglion along the middle
of the under part of the abdomen, attached to the ventral in-
tegument, and inclosed, as it were, by the great ventral vein.
Twenty- one equidistant rhomboidal ganglions are developed upon
these chords, which distribute their filaments to the adjoining
segments by two powerful diverging trunks on each side. The
segments indicated by the external circular indentations of the
integument are much more numerous than the ganglions. Dr.
Brandt has detected a simple nervous filament continued from the
oesophageal ganglion along the dorsal aspect of the alimentary
canal. This is an interesting structure, since it offers the first trace
of a distinct system of nerves, usually called the stomato-gastric in
Entomology, and to which our great sympathetic and nervus vagus
seem answerable.

The structure of the abdominal ganglion in the leech has been il-
lustrated by the microscope and pencil of Ehrenberg : in the centre
of the ganglion are several clavate corpuscles, the enlarged end of
each being formed by a nucleated cell, the tapering extremity is con-
tinued into the diverging nervous chords : the clavate cells are
arranged in eight groups, two groups being continued into each of
the four diverging chords of the ganglion : one of these groups may be
supposed to be the recipient, the other the transmitter, of impressions.

In the earth-worm the brain or supraoesophageal ganglion consists
of two lateral lobes, which send off" small nerves to the proboscis, and
the two large chords to the suboesophageal ganglion : some small
filaments are derived from the oesophageal collar. The two ventral
nervous trunks are more distinct from each other than in the leech ;
but the ganglions are relatively smaller and more numerous, corre-
sponding in number with the segments of the body. Two pairs of
nerves are given off" from each ganglion, and a third pair comes off
from the intermediate chords. The terminal or anal ganglion distri-
butes a plexus of nerves to that termination of the body.

In the Nereis the abdominal ganglions are more distinctly bilobed

ANELLATA. 143

than in the earth-worm, and the supra-oesophageal ganglion is rela-
tively larger, having to furnish nerves to both antennae and ocelli.
The pairs of ganglions developed upon the ventral chord correspond
with the segments of the body in number, and are very close together.
In the Eunice gigantea there are upwards of 1000 ganglia; but
this complicated condition of the nervous system is more apparent
than real, and, like the multiplication of the pulsatile sinuses of the
vascular system in the same animal, depends upon the vegetative
repetition of like parts without any mutual subordination in reference
to the performance of a special office.

In the Aphrodita the body is broader and thicker than in other
Anellides, and begins to exhibit that concentration which characterises
its form in the higher Articulata. But the segmental nervous ganglions,
though more closely approximated, are yet not confluent at any central
part. The brain is heart-shaped, having its bilobed base turned back-
wards and connected in the usual manner by large oesophageal columns
with the inferior ganglion. The antennal nerves are continued from
the apex. The visceral nerves are given off from the cesophageal
circle, and pass to the upper surface of the intestine, and there swell
into a small ganglion. The sub-oesophageal ganglion is of large size,
and bifurcates anteriorly : the second ganglion is situated close by the
first, and gives off' two pairs of nerves : the third to the fifteenth
ganglions send off" respectively three pairs of nerves, the first of
which corresponds with the inter-ganglionic nerve in the earth-worm,
and supplies the branchial organs ; the second pair is distributed
to the ventral muscles ; the third to the lateral and dorsal muscles.
The abdominal ganglions, which succeed the fifteenth, send off"
each two pairs of nerves, and gradually diminish and approximate
at the posterior extremity of the body. In this highly organised
Anellides the nerves may be distributed into those of special sense
(antennal), the excito-motory, the sympathetic or stomato-gastric,
and the respiratory.

The power of repairing injuries and reproducing mutilated parts is
considerable in the Anellides, and especially in the species of Lum-
hricus and Nais, in which it has been variously and extensively tested
by the experiments of Bonnet and Spalanzani. A worm cut in
two, was found to reproduce the tail at the cut end of the ce-
phalic half, and form anew head upon the caudal moiety. Bonnet*
progressively increased the number of sections in healthy individuals
of a small worm {Lumhricus variegatus) : and when one of these had
been divided into twenty-six parts, almost all of them reproduced
the head and tail, and became so many new and perfect individuals.

* CEuvres, vol. i. pp. 1 1 7—245. 4to. 1 779.

144

LECTURE XII.

It sometimes happened that both ends of a segment reproduced a
tail. Wishing to ascertain if the vegetative power was inexhaustible,
Bonnet cut off the head of one of these worms, and, as soon as the
new head Mas completed, he repeated the act ; after the eighth
decapitation the unhappy subject was released by deaths — the ex-
ecution took effect, — the reproductive virtue had been worn out :
this series of experiments occupied two summer months. Since many
of the smaller kinds of worms and Naids frequently or habitually
expose a part of their body, the rest being buried in the earth, both
they and their enemies profit by the power of restoration of the
parts which may be bitten off.

With this power of reproduction of lost extremities is associated
that of spontaneous fission in the genus Nais. In these little red-
blooded worms, the last joint of the body gradually extends and
increases to the size of the rest of the animal : its anterior part
begins to thicken and to be marked off by a deeper constriction from
the penultimate joint. In the Nais proboscidea a proboscis shoots
out from it, like that on the head, and it is then detached from the
old Nais. It often shoots out, previously to its separation, another
young one from its own last joint in a similar way, and three
generations of Naids may thus be seen organically connected, and
forming one compound individual. Distinct sexual organs are
developed in the Nais for both the formation and fertilisation of ova :
but the illustrations of the generative system in the preparations
^^ before you are derived from the leech, the earth-worm,
and a few of the dorsibranchiate Anellides.

The medicinal leech is androgynous, like the rest of
the Anellata; it has nine pairs of testes {Jig. 15, a, a),
two vasa deferentia (6, h), and two sacculated vesiculae
seminales (c, c), which send their ducts to a common
prostatic body (rf), from which the penis (e) is continued :
this filament projects from the middle of the ventral sur-
faces of the twenty-fourth ring, between the sixth and
seventh ganglion : a distinct slender ejaculatory tube is
continued along the middle of the intromittent organ.
Each testis is a round whitish sac,
I/O Qi containing a milky fluid abounding
I I with clear spherical corpuscles : a

i^ Oi] short duct carries the secretion to the
common longitudinal vas deferens.
The female organs {Jiff* 76.) lie be-
tween the seventh and eighth ner-
vous ganglia, and consist of two sphe-
rical ovaria (a) and two short oviducts Leech.

-Q

(M

Leech.

ANELLATA. 145

(b), which unite into a single longer tortuous tube (c), terminating
in an expanded fusiform uterus (d), which opens externally at the
twenty-ninth segment. The ovaria contain numerous round cor-
puscles, in which there are several germinal vesicles ; the parietes of
the uterus present both longitudinal and transverse muscular fibres.

The fertile ova of the medicinal leech are discharged in groups
of from six to fourteen, enveloped in a nidus or cocoon of mucus.
The cocoon is ovate, two thirds of an inch in length and half an
inch in diameter. It has a rough outer surface, but is smooth
and slightly tuberculate within. In the month of August conical
excavations may be observed in the slime at the sides of the reservoir^
in each of which there is a cocoon. In a few days after the ova have
been thus expelled and protected, the young leeches are extruded.
The formation of the cocoon has been observed by Dr. Johnson in
the rivulet leech (Hirudo vulgaris). In this species, when a cocoon
is about to be formed, the body is observed to be greatly contracted
both above and below the uterus ; the included part swells, then be-
comes milky white, from the formation of a film into which the animal,
having attached itself by its anal sucker, forces, with some effort, the
whole contents of the uterus. This being done, the leech elongates
the anterior part of the body, and thus loosening the enveloping mem-
brane, withdraws its head as from a collar. It sometimes bends back
its head, and, drawing the collar forwards, gently aids in its removal.
The j)rocess generally occupies about twenty minutes. The cocoon
is at first very elastic, and has no determinate figure. After the leech
has attached it to some adjoining substance, it fashions it with its
mouth into an oval form. The points of the cocoon from which the
leech withdrew its head are weaker than the rest, and from these the
young escape.

The earth-worm, like the leech, is androgynous : the testes are four
in number, of a subglobular figure, granular texture, and opake white
colour : their ducts open upon the external surface. Two other parts
are to be reckoned among the accessory organs of the male sex ; the
first are the imperforated penes or stimulating filaments, which may be
developed from the thirty-second to the thirty- eighth ring inclusive ;
their base adheres intimately to the cellular tissue : they have no
communication with the genital apertures, are developed only at the
breeding season, and are deciduous. The second accessory organ
is that thickened part of an earth-worm which is situated between the
thirtieth and the fortieth segments : it is called the clitellum, and
when two earth-worms are disturbed, the adhering clitella are the
last parts to give way. The ovaria are eight in number, arranged
four on each side. The ducts of each lateral series unite to form a

146 LECTURE XII.

convoluted oviduct, which opens upon the sixteenth segment of the
body. In spring the vitelline cells begin to multiply around the ger-
minal vesicle, in the form of minute dark specks ; towards autumn the
ova become red coloured, and, by their increase in size and number,
they render the surface of the ovarium irregular. At this season the
fertilising fluid reaches the ovaria by the ducts above described, which
are then filled with spermatozoa. The only function of the ducts is
to afford a route or passage to these moving filaments which, like
the pollen tubes in plants, attach themselves to the ova, and in such
numbers as, according to the observations of Dr. A. Farre, to give
the impregnated ova the appearance of a ciliated gemmule. The ova
escape, like the seeds of plants from the ovaria, by dehiscence of the
coats of those organs, not by passing outw^ards through the so-called
oviducts, which are analogous to the tubes in the style of a flower,
which give passage to the pollen filaments, but not an exit to the
seeds. The ova, after being expelled from the ovaria, pass into the
interspace between the sub-muscular membrane and the muscular
integument, and, by a series of strong undulations of the body, are
ultimately propelled to a receptacle near the arms. Here they un-
dergo a certain amount of development, and are frequently expelled,
like chrysalids, enveloped in a hard, yellow, pellucid, and slightly
elastic integument, probably an exuvial skin. Sometimes they are
expelled from the parent in this state : sometimes the young are ex-
cluded from their case before parturition.

With regard to those ciliated corpuscles already alluded to, as dis-
covered by Dr. A. Farre, in the ovaria of the earth-worm, similar
bodies have been detected by Mr. Quekett in the testes of the rivulet
leech. They occur with more numerous unciliated spherical cor-
puscles, and appear to represent groups of spermatozoa, analogous to
the bundles in which the same filaments are aggregated in the sperm
sacs of the medusa.

In the Arenicola, or sand- worm, the testes are situated in pairs at
the anterior part of the body, and the ova are discharged by dehis-
cence of the ovaria into the abdominal cavity.

In the genus Eunice, every segment, save the first, has its ovarium
and testes attached to either side, which reminds one of the multi-
plication of these organs in the Tcenice. The Aphrodites are stated
to be of distinct sexes.

The development of the ova in the class Anellata, has been hitherto
but little studied. Some of the few observations on record in refer-
ence to the dorsibranchiate order, indicate that they undergo, during
their development, a metamorphosis almost as remarkable as that of
insects. Dr. Loven obtained in the month of August in the Baltic

ANELLATA. 147

Sea, a discoid animalcule {fig^ 77.), which rapidly moved by means
of two rows of vibratile cilia : the principal row
being situated upon a projecting ring (5), at the
margin of the disc. This ciliated body differed from
the gemmules of the Polypi, in being provided with
a mouth {a) and an anus, the latter occupying the
apex of the cone (c). The course of the alimentary
canal (<i), which extended from one to the other
aperture, was detected by feeding the little ani-
mal with indigo. In a short time the cone began
to elongate and to be divided into segments, which
^ ^ ^ were developed in four parts, the two principal

Embryo of Nereis. ^ ^ ^ ^

pieces forming half-rings, one upon the upper, the
other upon the lower surface, which were united by two shorter lateral
pieces. Coincident with the elongation and segmentation of the body,
was the development of the head from the discoid surface (e), upon
which first the black ocelli, and then two pointed filaments, or an-
tennse (/), made their appearance. The length of the body, and
the number of segments, continued to increase, the disc with its
vibrating cilia still existing. This disc is afterwards reduced to an
appendage on each side of the head, and finally disappears. The
new rings are added in front of, and not behind, the older ones,
agreeably with the order of development of the segments in the Bo-
thriocephalic described in a former lecture. Each ring originally
consists of an upper {cf) and an under half ring (Ji), analogous to
the tergum and sternum in the external skeletons of Insects. The
tubular and setigerous feet are lastly developed from the small lateral
pieces. These observations beautifully exemplify the repetition of
structures and phenomena, characteristic of mature animals widely
separated in the natural scale, in the immature states of an interme-
diate species.

LECTURE XIII.

EPIZOA AND CIRRIPEDIA.

The naturalist has often been baffled or led astray in his attempts to
discover the real nature and aflftnities of an animal by investigations
limited to the structure and habits of such animal in its mature state.
There are some species which undergo such extraordinary metamor-

L 2

148 LECTURE XIII.

phoses before attaining that state as to mask their true relations, not
only to the class, but to the primary division of animals to which
they belong. This is especially the case with the creatures whose
organisation and development will form the subject of the present
lecture.

This elongated, cylindrical, unarticulated Lernaea* {fig' 78.),
g^ whose smooth soft body seems devoid of any other appendages
than the two long slender ovisacs, might be regarded as one
of the Entozoa of the fish to which it is attached, and on the
nutrient juices of which it subsists.

This barnacle, imprisoned in its conical calcareous shell,
and cemented to the stone on which it grew, might seem as
naturally to belong, like its neighbour the limpet, to the tes-
taceous Mollusca.
The most vivid imagination of the boldest generaliser or speculator
upon the unity of organisation in the Animal Kingdom could never
have divined that the Lernaea and the Cirripede were at one period
of their lives locomotive animals, swimming about under very similar
forms, and by almost identical natatory instruments ; not under the
common ciliated infusorial form, in which the young of certain
Entozoa and Mollusca first enter into active life ; but with sym-
metrical pairs of jointed setigerous legs like those of the lower
organised Crustaceans, to which the Epizoa and Cirripedia are, in
fact, essentially and most closely allied, although they end their career
as sedentary animals under such different, such diversified, and, as
regards the Epizoa, such grotesque forms.

These metamorphoses lead to very different results from those of
the Medusa and Comatula. The Epizoa and Cirripedes acquire
increase of bulk and organs of generation ; but, in every other
respect, the varied course of their development ends in a retrograde
movement. This development would seem to have been at first, as
it were, hurried forward at too rapid a pace, and the young parasite,
starting briskly into life, ranging to and fro by the highest developed
natatory organs we have yet met with, and guiding its course by
visual organs, must lose its eyes and limbs before it can fulfil the
destined purpose of its creation.

The Epizoa, by which name we recognise the singular class of
animals which infest the skin, the eyes, and the gills of fishes and
other marine animals, — these external parasites, which are as numerous
as, and perhaps more numerous than, the whole class of fishes, — are

* This name was applied by Linnaus to the genus or group including the para-
sitic animals now termed Epizoa, which are classed with the Mollusca in the
Systema Natura?,

EPIZOA.

149

distinguished in their mature state by a body of a more or less
elongated or sub-cylindrical form, defended by a smooth, semi-
transparent, parchment-like integument, having a more or less distinct
head, and generally a pair of long cylindrical ovisacs, dependent from
the opposite extremity of the body.

In this low organised class of Articulate animals, as in the classes
which commence all other great primary groups, there is an extensive
gradation of forms by which we pass from species
slightly elevated above the cavitary Entozoa to the
true Crustaceans.

The lowest or most simple Epizoa adhere by a
suctorious mouth {^fig. 79. «), and traces of extre-
mities exist only in the form of a few minute pairs
of obtuse inarticulate processes {h b). In the
j\ highest organised species, the adhesion is effected

by jointed mandibles with terminal hooks or for-
ceps. The head, in most of the species, is found,
when closely examined, to present a pair of jointed
antennae {Jig. 81. e), which, in the experienced na-
turalist, cognisant of the value of such characters,
might excite the suspicion that relations to higher
Articulata than the Anellides were hidden under
the bloated form which indolent and gluttonous
habits had superinduced upon the pendent parasite.
Observation of it during its early and independent
state has proved this to be actually the case to an
extent which could scarcely have been anticipated.
The Epizoa are of distinct sexes : the male {Jig.
82.) appears always to retain his freedom, and is,
perhaps on that account, singularly smaller than the
female, generally not more than a fifth part of her
size ; consequently, for a long time, the males es-
caped recognition. They adhere to the vulva with
one antenna usually inserted. The individuals
of the productive sex, distinguished throughout a
great part of the year by their pendent ovisacs, are
the examples usually seen of this curious class ;
and in these I shall proceed to describe the ana-
tomical characters of the Epizoa.

The body, independently of the ovisacs, is gene-
rally divided into two segments : the anterior and
smaller division sometimes supports a distinct head, but more com-
monly corresponds with the cephalothorax of the Crustacea; the larger

L 3

150 LECTURE XIII.

segment is called the abdomen, and in it the ovaria are developed.
You ^vill not unfrequently find adhering to the eye of the sprat an
Epizoon or Lernaea *, which is a nearly allied species of the same
genus {Peniculus), as the specimen figured and described by Nord-
man (Jig. 78.), which infests the boar-fish {Zeus aper). In the
Peniculus fistula the head {fig, 79, h) is oval, and notched anteriorly,
each division being armed with an inwardly bent hook, or rudimental
jaw. The mouth («) is immediately beneath these, in the form of a
circular orifice, supported by a short cartilaginous tube. At the
posterior contracted part of the head are two pairs of short, oval,
flattened processes : a constriction or neck separates them from the
thorax (^), at the commencement of which there is a third pair of
similar rudiments of locomotive appendages. The thorax is round,
and separated by a constriction from the abdomen {ab), a fourth
pair of appendages being developed from the interspace. The
alimentary canal {d, d) is much contracted in the neck and thorax,
but expands in the abdomen into a moderately wide and uniform
intestine, which again slightly contracts to terminate at the hinder
extremity. The alimentary canal has the same simple straight course
in other species of Epizoa. One cannot be surprised at this corre-
spondence with its general condition in the cavitary Entozoa, when
the similarity of their easily assimilable nutriment is remembered. It
is, however, complicated in the Epizoa, with a conglomerate or mi-
nutely-lobed glandular mass, developed from nearly the whole extent
of the abdominal tract of the intestine, and which may fulfil the
function of a liver.

In some species which attach themselves to the gills and the like
favourable positions for an abundant supply of the most nutritious
fluid, the body is frequently deformed, as it were, by excessive
growth, and cascal productions from the simple straight intestine are
continued into the prolongations of the thoracic or abdominal walls.
The Nicothoef, a small parasite of the gills of the lobster, is an
example of this condition of the digestive organ. The first segment
of the body is produced into two lateral symmetrical wing-shaped
lobes, each four times the length of the segment to which they are
attached, and they contain corresponding csecal prolongations of the
straight intestine.

In the species of Lernsea exhibited (Peniculus fistulci)-, the abdomen
contains, in addition to the alimentary canal, two slender tubes (o, o),
commencing by blind extremities near the anterior part of the dilated
intestine, and continuing with a slightly wavy course to terminate at
the two apertures,, to which the ovisacs (/) are attached.

* No. 287. A.

t Audouin and Edwards, Crustacecs, 1829, 8vo. p, 1,

EPIZOA.

151

These ovisacs singularly resemble the seed-capsules of certain
plants, especially the Cassia fistula^ being divided into a series of
cells or chambers by transverse septa, placed at regular distances.
Each cell contains an elliptical or lenticular ovum.

Two slender white filaments (^, ^) running almost parallel with, but
at a distance from, each other, through the whole length of the under
surface of the abdomen, nearer the margins than the middle line, form
the chief and most conspicuous part of the nervous system.

The most common mechanism of adhesion in the Epizoa is a cir-
cular sucker, developed upon the confluent extremities of a pair of
obscurely jointed tubular feet, as in this Lerneopoda of the Shark *,
in the Achtheres of the Perch {fig. 81.), the Tracheliastes of the
Chub, <Src. In the last-named parasite, which may be found adhering
to the fins of the Chub in the months of October and November, the
head and thorax are confluent, unless the segment to which the bases
of the before-mentioned feet are attached be held to represent the
thorax. The abdomen isj as usual, the largest segment. The mouth
{fig. 80. «) is a circular aperture, fringed with minute short bristles ;
on each side there is a maxilla (e) dentated at the inner margin, and

terminated by a bifid hook. The
antennae (/) are represented by
two short lancet-shaped processes
terminated at the apex by a few
extremely short bristles. The most
conspicuous appendages of the head
are, however, a pair of mandibles
(6), which consist of two obscure
joints, the second of which has a
bifid extremity ; the outer division
(c) is armed by a strong curved
spine, which is opposed to two
short straight spines; the inner
division (d) is tipped with four
small spines. Immediately behind
the large tubular prehensile pro-
cess is a short rudimental extremity, supporting a moveable hook,
which is opposed, as in the mandibles, by two short spines. The
muscular system is sufficiently conspicuous in the head of this Epizoon
in the form of distinct fasciculi of fine fibres (^.)

In this Penella\ the head resembles a cauliflower, swelling out into a
globose group of slightly branched and obtuse wart-like processes,

Tracheliastes.

* No. 286. A.

t No. 286.

L 4

152

LECTURE XIII.

which must have grown after the head had become imbedded in the flesh
of the fish to which it is attached. Two long tubular processes or ex-
tremities are developed at the junction of the thorax with the abdomen ;
but their extremities are free, simple, slightly attenuated, and obtuse.
On the under surface of the body in the interspaces of these appendages
there are four pairs of simple, small, oval, flattened feet ; their pointed
extremities extend only half way to the sides of the part of the body
to which they are attached. The body is prolonged beyond the ovi-
sacs in the form of a tail, which is provided on each side with a series
of sixteen slender cylindrical appendages, close set in an oblique
position, like the barbs of a feather, or the vane of an arrow, whence
the specific name Sagitta, given to this parasite. The caudal la-
mellae of the higher Crustacea would seem to be here sketched out.
The anatomy of the Epizoa has been most elaborately traced out
by Nordmann in the parasite of the com-
mon perch, called Achtheres, In this
species two lateral teeth project from
the circular mouth, the labial margin of
which is fringed with bristles. Here
also we have mandibles and maxillae, the
latter provided with palpi ; and besides
these, a pair of jointed antennae {Jig- 81.
«), each terminated by three setae. The
hepatic organ (e) is more concentrated
than in the Peniculus, and surrounds the
anterior part of the canal. The aliment-
ary canal is, as usual, straight, and ter-
minated by a bituberculate vent at the
opposite extremity to the head. The
abdominal intestine (^d) is fusiform, and,
divided by a series of slight constrictions^
into sacculi. It is maintained in its po-
sition by a transverse muscle (Ji). The
walls of the abdomen are distinctly pro-
vided with longitudinal {i) and transverse
(k) fasciculi of muscular fibres. The
nervous "system consists of a single ce-
phalic ganglion, from which are conti-
nued two principal chords {g g) extend-
ing along the under surface of the body.
The circulating fluid consists of a
clear plasma, with granular corpuscles
The pulsatile vasiform heart may be

Achtheres, female, magnified.

of different forms and sizes.

EPIZOA. 153

seen at the middle line of tlie cephalo-thorax propelling the blood
forwards by rythmical contractions. Two canals (??, n) pass from
it into the hollow prehensile feet. The rest of the blood is dis-
tributed to the head, and along each side of the commencement of the
alimentary canal to the under part of the body, where it passes back-
wards in the vessel which accompanies the intestine.

The ovaria (o, o') at first appear in the form of a slightly flexuous,
long, blind tubes, sacculated along one side. As the ova are developed,
the ovarium takes on the form of a bunch of grapes, and occupies the
whole cavity of the abdomen external to the intestine : each ova-
rium terminates by a triangular, and somewhat prominent orifice,
to which the external ovisac (/) is appended.

In the minute male {fg. 82.), the testes are indicated by four dark-
coloured and finely granulated bodies situated in
the posterior segment or abdomen.

The first remarkable circumstance in the natural
history of the aquatic Epizoa is the constancy with
which particular species infest particular fishes or
Crustacea. And how, it may be asked, can creatures
so devoid of means of transport, nay, in most in-
stances, of the power of detaching themselves from
Achtheres, male, the auimals wheucc, like foetuses, they derive their
magni ed. mcans of growth, originally reach the precise species

of animal and organ to which they are habitually attached ?

Are certain of the ova accidently retained near the parent after
the rupture of the ovisac, and there grow, like seeds of plants fallen
in a favourable soil ? Or, do some of the liberated ova, by a happy
fortuity, arrive at the appropriate organ of the appropriate species?
and are they there accidentally retained until the prehensile instru-
ments are developed ? Such hypotheses may be permitted in reference
to the ova of an Entozoon which are developed by millions, and need
only to be swallowed by the animal in whose intestine they are
adapted to exist, but the ova are too few in the Epizoa, and the parts
to which they are attached are too exposed, to allow of the suppo-
sition that their parasitic growth is dependent on such accidental
circumstances. M. M. Audouin and Edwards appear to have
been the first to suggest that the sedentary Lernaean Epizoa might
enjoy at a previous period of existence locomotive powers, and the
hypothesis was supported by the discovery, made by Dr. Surriray, of
the embryo of a Lernceocera, still in the ovum, which, instead of re-
sembling the parent, presented the characters of a locomotive
Entomostracous monoculous Crustacean.

The singular metamorphosis thus indicated has been traced out

154

LECTURE XIII.

and generalised by the careful observations of Dr. Nordmann. The
following is the general course of development of the Lernaean parasite
of the Perch.

The female Achtheres is devoid of ovigerous appendages in the
months of December, January, and February. In March they are
developed by the eversion of a membrane prepared in the ovarian
sac. Each sac hangs by a short tubular peduncle which is in direct
communication with the short oviduct. The outer membrane of the
ovum or chorion is moderately thick and transparent ; the inner
membrane is thinner, and includes both the vitelline mass and albu-
men. The yoke forms the largest proportion of the contents of the
ovum, and is finely granular. One of the first parts of the embryo
discerned by Nordmann was the dark ocellus {fig. 83. ci). A pair of
cylindrical processes shoot out from each side of the
fore part of the embryonic or vitelline mass ; and a
pencil of hairs is developed from the extremity of
each process. The body slightly elongates ; the
exterior albuminous fluid inceases^ the inner mem-
brane expands^ and the outer one bursts and is shed.
The movements of the imprisoned embryo increase
in force until it bursts the remaining membrane of the ovum and

escapes from the ovigerous sac. It
then presents the form represented in
figure 84. ; the digestive sac (Ji) is now
'^Z/ '^]Sr'"^j!| ^^ discernible, together with a peculiar tor-

tuous tube (^), which is continued from
the eye-speck. In the course of half an
hour the young Achtheres undergoes its
second stage : the first integument is
loosened by the formation of a second beneath it, which now incloses
a body, altered in its shape and in the number and
nature of its appendages.

The process of moulting lasts from eight to ten
minutes. The body {fig. 85.) is divided into an
anterior and a posterior segment, the latter con-
sisting of four joints. A pair of four-articulate se-
tigerous antennae diverge from the anterior part
of the body. Between the antennae is the large
single median eye, as in the monocular Entomo-
stracous Crustacea. The little Epizoon is now pro-
vided with five pairs of feet, the first three pairs
terminate by a simple hook ; the last two pairs are
bifurcated, one division being hooked and prehensile, the other

CIRRIPEDIA. 155

tubular and emitting tufts of bristles : these natatory feet strike the
water together, and propel the body forward with a jerk : they are
aided by the last segment, which is terminated by four setigerous
tubercles.

The antennse probably serve to indicate to the young parasite its
appropriate object, to which it then proceeds to attach itself. The
second pair of feet increases in size, and the terminal hook enlarges :
the feet of the third pair lengthen and unite together to form a
cartilaginous circular sucker. The first pair of feet is approximated
towards the mouth, and forms the uncinated mandibles.

The two sexes are alike in their young and locomotive state : the
male at its final metamorphosis retains the first pair of feet as man-
dibles, very similar in form to those in the female : the second pair
is shorter and thicker : the legs of the third pair always remain
separate from each other, and consists usually each of two large
joints, the last one terminated by a claw. The posterior natatory
feet disappear in both sexes.

CiRRIPEDIA.

Many of the Cirripedia are parasitic animals, like the Epizoa, but
are dependant upon the organised bodies to which they are attached
for their place of residence, not for their food : those species which
do not infest other animals are attached to sea-weed, floating timber,
or rocks. The Cirripedes are symmetrical animals, with a soft
unarticulated body enveloped in a membrane : they are provided with
six pairs of rudimentary feet, obscurely divided into three joints, and
terminated each by a pair of long and slender many-jointed, ciliated
tentacles, curled towards the mouth, and thence giving origin to the
name of the class.

The mouth is provided with a broad upper lip, with two palps or
feelers, and three pairs of dentated and ciliated jaws. The opposite
extremity of the body is prolonged into a slender many-jointed ciliated
caudal appendage, which is traversed by the generative canal. The
mouth is situated near the anterior extremity of the body, which
is modified to form the organ of attachment of the animal. It i&
sometimes produced to a considerable extent, and is of contracted
diameter, forming a long and flexible peduncle ; sometimes it expands
at once into a broad disc or basis of adhesion. The Cirripedes are
divided according to these modes of attachment into two primary
groups, — viz. the pedunculated, or Lepadoids, and the sessile, or
Balanoids. The first are commonly known by the name of Barnacles ;
the second by that of Acorn-shells.

156 LECTUEE XIII.

Most of the Cirripedes have their visceral cavity protected by a
calcareous shell composed of many pieces ; but in some, as the Otioii,
the membranous or pallial investment of the viscera is protected only
by an elastic horny sheath, continued from the epidermal covering of
the peduncle. Two small calcareous bodies, developed in the sub-
stance of the outer envelope, just above the brachial fissure, are the
sole rudiments of a shell in this genus, the horny covering of which
is produced at its free extremity into two cylindrical processes. In the
genus Cinerasy the external tunic is strengthened by five calcareous
bars, two at the ventral fissure, giving outlet to the arms, two along
the terminal margin of the tunic, and one along the dorsal aspect.
In the common Barnacle {Lepas anatifera) the calcareous matter
extends from fine centres, so as to protect the whole of the body,
which is appended to the peduncle : the cephalic pair of valves, or
that which is attached to the peduncle and defends the head, is
the largest : the single dorsal piece has been compared by Cuvier,
who retained the Cirripedes among the MoUusca, with the sym-
metrical dorsal valve in the shell of the Pholas. All the valves are
strongly marked with lines of growth, formed by successive additions
to their margins, as in the shells of MoUusca. In the Pollicipes there
are other smaller calcareous plates arranged round the junction of the
body with the peduncle.

All the sessile Cirripedes are strongly defended by a multivalve
conical shell. The base of the shell is usually formed by a calcareous
plate, and the walls are apparently divided into twelve conical com-
partments, six of which rise from the margin of the base, and ter-
minate in a point at the free margin of the shell ; whilst the other six,
in the form of inverted cones, occupy the interspaces of the preceding
series. This calcareous citadel is divided into six pieces by six
sutures : the symmetry or bilaterality of the shell is determined by
the dorsal piece being actually what each of the six pieces of the first
series seem to be, viz. a simple triangular plate with its apex upwards :
the two lateral pieces on each side consist each of the erect and
inverted triangular piece closely united together : the ventral piece
consists of one erect and two inverted triangular pieces, united
inseparably in the mature Balanus. The whole shell has a cellular
and organised texture, and its gradual expansion is provided for by
the successive growth and calcification of processes of the mantle
which penetrate the uniting sutures. The cone is lengthened and
widened below by successive additions to its base, and is widened su-
periorly by the gradual increase in breadth of the wedge-shaped pieces
of the second, or inverted series. In the Tuhicinella*^ ^ a parasitic

* Prep. No. 279.

CIRRIPEDIA. 157

Balanoid of the whale, the compound shell is long, subcylindrical,
and wider above than below. The upper aperture is closed by an
operculum of two or more shelly plates.

The animal in both sessile and pedunculate Cirripedes, is fixed to
the bottom of the shell with its head downwards. The head is there-
fore superior in the ordinary pendant position of the Barnacle.

The movements of the peduncle in such species are effected by a
strong muscular tunic, as shown in these preparations. * The action
of these muscles is antagonised by the elasticity of the external horny
tunic. The common Barnacle approximates its large pair of valves
by a strong transverse adductor muscle ; the body or visceral mass
of the Barnacle is moved towards the aperture of the shell, which is
thereby at the same time widened by longitudinal muscular fibres,
and is retracted by shorter fibres attached to its base. The cir-
rigerous arms have powerful muscles for their actions, which are of
the utmost importance to the animal, inasmuch as the food is obtained
by the currents which they produce, and almost incessantly maintain,
in the surrounding water. The sessile Barnacles are provided with a
series of muscles attached to the margin of the conical shell, which act
on the opercular calcareous pieces, and close the opening of the shell.

The nervous system, as shown in this dissection of the Lepas vitrea
by Mr. Goadby, corresponds with that which has been described and
figured by Cuvier in the common Lepas anatifera. The oesophagus
is surrounded by a wide oval ring, at the sides of which are placed
the small ganglions, which supply the first pair of feet. The ring is
completed below by the ganglions of the second pair of feet. The
fifth and sixth pairs of ganglions are approximated to each other :
there is no cerebral ganglion ; but filaments are given off from the
supra-oesophageal loop, to the peduncle and sides of the head : two of
these branches pass to a small ganglion on either side near the
stomach, from which the digestive system is supplied : the tubular ex-
tensile tail receives the two last pairs of nerves. The nervous system
is perhaps the only part of the organisation of the mature animal which
unequivocally indicates the relations of the Cirripedia to the primary
divisions of the Animal Kingdom ; it is homogangliate : inferior to that
of the Anellides in the low development of the cerebral or supra-
cesophageal part, but nearer the crustaceous type in the large size of
the ganglions on the abdominal chords. In the degree of approxima-
tion of the two chords to each other, the Lepades most resemble the
lower isopodous Crustacea, for example, the Talitrus. The neuri-
lemma is stained by a dark brown pigment in the Lepas vitrea.

* Nos. 62. 68, 69.

158

LECTURE XIII.

Although the Cirripedes in their mature state possess no distinct
organs of sight or hearing, yet they are endowed with sufficiently
acute sensation to retract their cirri, and, if sessile, to close their
opercules, at the sound or vibration of an approaching footstep ; the
same actions indicate that they appreciate the atmospheric movements
produced by the approximation of the hand, even, according to Dr.
Coldstream, when it is not brought nearer the shells than twelve or
fourteen inches.

The marine animalcules brought to the mouth i^fig. 86. «), by the

currents of the cirrigerous
feet (h) and seized by the la-
teral jav>s, are conveyed by a
short oesophagus to a dilated
stomach (c), which receives
the ducts of two salivary
glands.. Groups of hepatic cseca
are developed from the walls
of the stomach. The intestine
(c?) is bent upon the stomach,
and tapers with a slightly
sinuous course to terminate
at {d) the base of the caudal
appendage (e). According to
M. St. Ange, the intestinal
canal of the Lepas contains
a membranous tube, which is
continued above into the se-
cerning cells in the walls of
the stomach; it may be the detached epethelium; it has been
deemed analogous to the typhlosole in the earth-worm's intestine.

A dorsal vessel and circulating currents along a double canal in the
arms have been recognised ; but the circulating system has not been
thoroughly investigated. In the pedunculated Cirripedes slender
conical branchiae (/) are attached to the base of the maxillary foot,
and to that of some of the cirrigerous feet. The ordinal distinction
between the pedunculated and sessile Cirripedes is not less strongly
manifested by their outward forms than by the branchial organs, which,
in the Balanoids, consist of two or more broad, transversely plicated,
vascular membranes, attached to the inner surface of the mantle.

The organs of generation in the Cirripedes have been differently
described by different authors. If the Cirripede be dioecious, and the
males be free and of a disproportionately minute size, as in the Epizoa
and in most Entomostraca, to which the Cirripedes are closely allied.

Lepas.

CIRKIPEDIA. 159

we must then regard the organs of generation in the large attached
individuals under a different and more simple point of view than they
have hitherto been described. The males are, however, wholly hypo-
thetical : they have not, hitherto, been seen, or at least recognised, as
such. In the pedunculated Cirripede, a large granular, glandular
mass, covers the viscera immediately beneath the muscular tunic of the
body, extending from the mouth to the anus. Its numerous ducts
successively unite into three or four principal trunks, which terminate
in a lateral receptacle {g) at the side of the intestine. In Lepas a
duct is continued from this receptacle on each side, which ducts unite
to form a common tube (A), which passes through the canal of the ex-
tensile tail. In Otion the two canals are continued distinct to the ex-
tremity of the process. The walls of the receptacle, which is the
common termination of the ducts of the lateral glandular body, are
thick and glandular.

According to Cuvier and Dr, Burmeister these glandular parietes
of the ducts of the gland constitute the testis, and the glandular
mass itself is the ovary. The ova are impregnated in the course of
their passage through the common receptacle, and the duct continued
from it.

On the dioecious hypothesis, we must suppose that the large fixed
individuals are females ; that the ovarium exists under the form and
situation in which it is described by Cuvier; and that the supposed
testis, which makes its appearance in a very questionable form as a
glandular tunic of the oviduct, is actually a nidimental gland, and
adds an exterior covering to the essential part of the ovum.

But ova are certainly developed in the pulpy substa,nce of the
peduncle. These, however, in Cuvier's view of the organs, are sup-
posed to be impregnated ova, conveyed by the extensile tail or ovi-
positor into the cellular texture of the peduncle. On the dioecious
hypothesis the ova of the peduncle must also be supposed to be con-
veyed by the ovipositor from the lateral ovaria, but to be impregnated
by the males hi transitu.

Another explanation of the parts in question has been offered, on
the assumption that both sexes are combined in the same individual :
the part described by Cuvier as the ovarium is held to be the testis;
the dilated canal into which its ducts converge is a spermatic recep-
tacle ; its glandular walls a prostatic organ ; and the terminal flexible
and extensile tube (Jig. 86. e), the penis. The true ovarium is situated
in the peduncle, to the soft tissue of which the ova unquestionably ad-
here when first developed. It is here that they acquire the azure or
violet-coloured yolk ; and from this part they subsequently pass into
two leaf-shaped receptacles, placed one on each side, between the body

160 LECTURE Xlll.

of the animal and the lining membrane of the shell. The ova are doubt-
less impregnated in attaining this situation : here they increase in size,
and change their colour to pink and then to white : the embryos are
here developed, and, after their escape, all traces of the temporary
receptacles disappear. This view of the generative organs seems to be
the true one, provided the Cirripedes be androgynous.

V/hen we reflect on the uniformity of distribution of the Cirripedes,
particular species being attached to particular objects, and these not
always stationary and extended bodies, but often living animals, and
sometimes animals with quick powers of locomotion ; when we further
call to mind that they adhere, not by prehensile jaws or feet, but by
the growth of a pedunculated root, or by the gradual application of a
layer of cement forming the base of their shell, we must be convinced,
that the organization and properties of the sedentary Cirripede are
wholly inadequate to afford an insight into the process by which it
acquired its resting place, and, that a knowledge of its previous career
from the time of quitting the egg is not less essential to an explanation
of the subsequent attachment of the Cirripedia, than it was for the elu-
cidation of corresponding phenomena in the Epizoa.

No fortuitous dispersion of ova giving origin at once to a pedun-
culated or sessile multi valve can account for the invariable attachment
of the Coronula to the skin of the whale, and of the Otion to the shell
of the parasitic Coronula ; of the Chelonohia to the carapace of the
turtle, of the Cineras to the tail of the sea-serpent, or of the imbedding
of the Acasta in the substance of a sponge. These remarkable phe-
nomena have been explicable only since the discovery of the singular
metamorphoses which the Cirripedes undergo, and of the pow er which
they possess at one period of their existence of attaining and selecting
their peculiar and appropriate place of permanent abode. Nor were
the real nature and affinites of this singular shell-covered class of
animals less problematical and doubtful before the phenomena of
their development had been traced out.

Mr. V. Thompson, w^hose mi-
nute and careful researches
into the natural history of ma-
rine animalcules have thrown
so much light on the structure
and development of radiated
Young of Baianus. auiuials, was also rewarded by

the discovery of the metamorphosis of the Cirripedes. On the 28th
April, 1823, he captured, with a small muslin towing net, a number of
translucent animalcules (^fig. 87.), about the tenth of an inch in length,

CIRRIPEDIA.

161

of a sub-elliptic form, slightly compressed, and of a brownish tint :
the body of each was defended by a shell composed of two valves,
joined by a hinge along the back, and opening along the opposite mar-
gin for the protrusion of a large and strong anterior pair of limbs («),
provided with an adhesive sucker and hooks, and of six pairs of pos-
terior jointed members (b), terminated by a pencil of bristles. These
natatory limbs acted in concert, so as to cause the animal to swim
by a succession of bounds like the water- fleas {Daphnia). The
body was terminated by a short tail (c), composed of two setigerous
joints. A pair of pedunculated compound eyes (d) was attached to
the anterior and lateral part of the body. Other specimens of this
little seeming crustaceous animal were taken on the first of May and
preserved alive in a glass vessel of sea-water. On the night of the
eighth two of them had thrown off their outer skin, and were firmly
adhering to the bottom of the vessel, where they rapidly assumed the
form of the young of the sessile Barnacle called Balcmus pusillus.
The sutures between the valves of the shell and of the operculum
were visible, and the arms, though not yet perfectly developed, were
seen moving within. The eyes also were still perceptible, although
the principal part of the black colouring matter appeared to have been
thrown off with the exuvium. On the tenth of May another indi-
vidual was seen in the act of throwing off its exuvium and attaching
S8 -^ /_ itself to the bottom of the

glass. As the calcification of
the shell proceeds, the eyes
gradually disappear and the
visual ray is extinguished for
the remainder of the animal's
life. The arms at the same
time acquire their usual ciliated
structure.

The LepaSy in its transitory
locomotive stage (y?^. 88.), does
not, like the young Balani, re-
semble the bivalve Ostracoda,
but rather approximates to the
genus Cyclops.^ It has a single
median sessile eye-speck (ct);
three pairs of members, the
most anterior of which {a, «,)
Young Lepas. are simple, the others (6, b,)

* See Mr. Thompson's Memoir, Philos. Trans. 1835.

162 LECTURE XIV.

bifid. The back of the animal is covered, like the Argulus armigery
by an ample shield, terminating anteriorlj'- in two extended horns,
and posteriorly in a simple elongated spinous process (c).

The discoveries of Mr. Thompson have been confirmed by Audouin,
Wagner, and Burmeister. The latter entomologist divides the de-
velopment of the Cirripedes into five stages. The first is that of the
ovum, the second of the locomotive embryo, the third when the
young attaches itself and becomes encased in a shell, in the fourth
stage it gradually assumes the character of the adult, and the fifth
stage is that of perfect development.

The locomotive embryo is developed before the ovum quits the
parent : the shell, in the first stage of its growth, is coriaceous, and
formed of one piece, which is placed on the back. The organs by which
the young animal fixes itself are the long antennae, or setigerous legs,
situated near the mouth : in the Lepas anatifera the peduncle is formed
by a sac-shaped process of the mantle filled with yellowish matter.

The general course of this metamorphosis, and the enjoyment of
locomotive and visual organs for a brief period, which are wholly
denied to the full-grown animal, characterize a condition which is
closely analogous to that of the young in the Epizoa, in the Trematoda,
and, with the exception of the visual organ, to the metamorphosis of
the sessile Polypes.

LECTUEE Xiy.

CRUSTACEA.

In the part of the Animal Kingdom which we have hitherto surveyed,
we have seen the organs of the vegetative functions rapidly acquiring
high and complex conditions, and again sinking to a primitive and
simple type. The digestive canal may present an oesophagus, a giz-
zard, a glandular stomach, and an intestine in a polype, and then be
reduced to a radiated sac, with one aperture in the star-fish. The
development of the organs for the propagation of the species is sub-
ject to a like oscillation ; the dioecious condition is early acquired, and
all the accessories to the essential glands, even marsupial sacs ; but
the generative system again subsides to an androgynous combination
of simple ovaria and testes in the red-blooded worms.

The organs of the animal functions manifest a steadier and more

CRUSTACEA. 163

constant progress, although it be slow and gradual. We have seen
the external skeleton assuming a symmetrical and jointed structure
in the Anellides, although consisting as yet only of a simple series
of rings : we have seen it provided with jointed organs of locomotion
and exploration in the Epizoa ; though here, indeed, the advance
was but transitory, and both organs and faculty of spontaneous motion
were quickly lost. In the Cirripedes, jointed appendages to the body
are retained, but their rapid actions are subservient to the acquisition
of food, not to locomotion.

We now arrive at a class of articulated animals in which the an-
nular segments of the skeleton of the body are constantly provided
with articulated limbs or appendages; in which all the species are
free and locomotive, and are provided with distinct respiratory organs.
These animals are still, however, aquatic ; only a part of the class
can support themselves and move with their jointed limbs on dry
land ; the highest act of locomotion is that of climbing reeds or trees,
which a few species of the present class are enabled to effect by long
prehensile claws. But the breathing organs in all the species are or-
ganised for aquatic respiration ; in other words, are branchiae ; and
it is the combination of branchiae m ith jointed limbs and distinct sexes
which constitute the essential characters of the class Crustacea.

The name of this class refers to the modification of the external
tegument by which it acquires due hardness for protecting the rock-
dwelling marine species from the concussion of the surrounding ele-
ments, from the attacks of enemies, and likewise for forming the
levers and points of resistance in the act of supporting the body, and
moving along the firm ground. In the crab and lobster tribes the
external layer of the integument is hardened by the addition of earthy
particles consisting of the carbonate, with a small proportion of the
phosphate of lime. This crust is coloured by a pigmental substance,
diffused more or less irregularly through it ; and it is formed upon
and from a vascular organised membrane, or corium, which is lined
by the smooth serous membrane of the visceral cavities. In the
smaller Crustacea the tegument retains a flexible, horny? or perga-
meneous texture.

Whatever be the consistence of the external integument or skeleton,
it is always disposed in a series of segments, either actually separate
and moveable on each other, or confluent in a variable extent and de-
gree, so as more or less to obliterate the traces of their primitive dis-
tinctness. The results of very laborious and extensive study and
comparisons of the modifications of the external crust of the diver-
sified forms of the present class have been generalised with much
success by Dr. M. Edwards^ who has shown that most of the Crus-

M 2

164

LECTURE XIV.

tacea manifest their peculiarlj^ distinctive forms by different combi-
nations and proportions of the same number of primary rings or
segments. Each ring, again, consists of certain elementary parts,
which, by varying their proportions, contribute to the peculiar form
of the region of the body, into the formation of which they enter.

There may be distinguished in the annular segment of a Crus-
tacean, a dorsal arch and a sternal arch, each consisting of a median
and two lateral elements: the lateral elements in the upper arch
are called " epimeral," and in the lower one " episternal," pieces ;
the middle element above, or " tergum," consists of two pieces
united in the middle line, and that below, or the " sternum," has the
same structure. In a great proportion of the class the body consists
of twenty-one of these rings, of which seven are more or less blended
together to form the head (^fig- 89, c), seven more obviously enter
into the formation of the thorax (^j^)j and the
remaining seven constitute the abdomen or
tail (a h).

The Crustacea, with seven thoracic and seven
abdominal segments, form the sub-class Malacos-
traca ; but a few large species and a very great
proportion of the smallest members of the class
have the thorax and the abdomen composed re-
spectively of a greater or a less number of con-
stituent segments than seven : these Crustacea
form the class Entomostraca, which is subdivided
into the Xiphosura, in which the last segment of
Cymothoa. the body forms a long three-edged sharp-pointed

weapon, and into the Entomostraca proper.

The Xiphosura, typified by the Limulus or Molucca crab, have the
head and thorax more completely blended together than in the true
crabsj which they resemble in the general form of the body; but they
are peculiarly distinguished from all other Crustacea by having the
office of jaws performed by the first joint of the thoracic legs, which
surround the mouth. The large cephalo-thoracic segment is protected
above and laterally by an expanded semilunar shield, obscurely di-
vided by two longitudinal impressions into three lobes, supporting
the organs of vision on their highest part. The tergal parts of the
segments of the second division of the body are also blended
into one trilobate clypeiform piece, their original separation being
indicated by the branchial fissures, and the number of the segments
by that of the lamelliform appendages attached to their inferior sur-
face. The termination of the intestine beneath the last segment of the
second division of the body of the Limulus proves that division to

CRUSTACEA. 165

answer to the abdomen in the iMalacostraca : but, admitting the ses-
sile eyes to indicate a distinct segment, not more than sixteen seg-
ments can be determined by the appendages to enter into the com-
position of the entire crust of the Limulus, including the sword-
shaped appendage, which is analogous to the last or post-anal segment
of the higher Crustacea, and consists of a single modified segment.

In the small Entomostraca, the number of the thoracic and ab-
dominal segments generally exceeds that in the Malacostraca. The
Branchipus stagnalis, for example, has eleven thoracic segments, and
nine abdominal or caudal rings, besides a distinct head protected by
a cephalic shield. In the Isaura, in which this shield is developed,
as in the Cypris, DapJmia, and other Entomostraca, to the extent,
and in the form, of a bivalve shellj enveloping the whole body, the
number of thoracic and abdominal segments exceeds twenty -four.

The distinction between the Entomostraca and Malacostraca in the
number of the segments of the body is of the first importance in de-
termining the affinities of the ancient extinct Crustacea, called Tri-
lobites. These remarkable animals were almost the sole represen-
tatives of the present class in the periods which intervened between
the deposition of the earliest fossiliferous strata to the end of the coal
formation.* They appear to have been without antennae and feet; the
structure of the tergal part only of their body-segments is yet known ;
but these are grouped together to form a distinct head, thorax, and
abdomen or tail. The head is formed by a large semicircular or
crescent-shaped shield ; the thorax consists of from ten to fifteen seg-
ments ; and the abdomen or tail includes at least eight segments in this
Ccdymene f , in which it is bent under the thorax, as in the crab : the
abdomen, post-abdomen or tail, as the third segment is variously
termed, contains fifteen fettered segments in the Asaphus caudatus :
the segments of both thorax and abdomen are very similar to each
other, and gradually decrease in size. They are divided by two lon-
gitudinal furrows into three lobes. The head supports a pair of large
compound eyes situated near the sides, like the large outer pair of
eyes in the Limidus, which they resemble in form and structure.

The Malacostraca are divided into two groups, according to the
attachment of the eyes : those with immoveable sessile eyes form the
Edriophthalmay those with moveable pedunculated eyes the Podoph-
tlialma.

The lower organised or edriophthalmous forms of malacostracous
Crustacea resemble the Trilobites in the non-confluence and uniformity

* Buckland, Bridgwater Treatise, i. p, 390. f Prep. No. 208.

M 3

166 LECTURE XIV.

of the segments of the thorax, and abdomen. Certain genera, as Se-
rolls and Bopyrus^ have the tergal arcs of the segments trilobed ; but
they exceed not the characteristic number in the Malacostraca, and
the seven rings of the thorax are clearly indicated in each by the seven
pairs of articulated feet which they support, although these are very
small in the parasitic Bopyriis. In the Cymothoa {Jig. 89.) the seven
thoracic and seven abdominal segments are more distinctly charac-
terised.

The seven segments of the head are rather indicated by the ap-
pendages of that part than demonstrable in any of the Crustacea.
The Stomapoda afford, in the genus Squilla, the most favourable ex-
amples for studying the conformation of the head. The first segment
supports the pedunculated eyes : the second the smaller antennae :
the third and fourth segments are confluent, but indicated by the
larger pair of antennae and a pair of mandibles ; the tergal part of these
confluent segments is greatly developed, and extends over the rest
of the head and part of the thorax. Three other pairs of jaws indicate
the rest of the seven cephalic segments ; and these are succeeded by
the seven thoracic rings and their articulated appendages.. Of these
the first two pairs, which are organised for locomotion in the isopods
and amphipods, are now modified to serve as jaws ; and the remain-
ing five pairs are reserved for locomotion in all the podophthalmous
Crustacea. The first of these five ambulatory thoracic legs is com-
monly the largest, and didactyle. They all consist of six joints, and
have usually two appendages attached to their base, called the palp
and flagellum : analogous appendages are attached to most of the tho-
racic and cephalic articulated appendages, which subserve as jaws.

The tergal arc of the third and fourth cephalic segments extends
over all the thoracic segments in the macrourous and brachyurous
Crustacea, and constitutes the broad carapace in the crab. In most
Macroura the thoracic shield is formed of the lateral or epimeral ele-
ments of the fourth cephalic ring, which meet along the back, and
give way preparatory to the moult. The tergal elements of the tho-
racic rings are not developed in either crabs or lobsters ; when these
rings are exposed by lifting up the cephalo-thoracic shield, the epi-
meral parts alone are seen converging obliquely towards one another
but not joined at their apices. The thoracic legs, besides serving for
mastication, prehension, and locomotion, usually support more or
less of the branchial apparatus, and certain pairs are perforated by
the generative ducts, except in certain crabs, in which the sternal
arc, which is of unusual breadth, supports the generative outlets.

The external arcs of the thoracic segments send inwards certain
processes, called apodemata, which include spaces for protecting the

CRUSTACEA. 167

abdominal nervous chords and the branchiae, and give origin to the
muscles of the legs.

The seven abdominal segments are always united by flexible joints,
and have no apodemata. In those Crustacea in which the thorax
and its cephalic shield are small, the abdomen is long, and character-
izes the great tribe of Podophthalnm called Macroura ; in those in
which the thorax and its shield are greatly expanded, the abdomen is
very short, as in the crabs, or the tribe hence called Srachi/ura ; this
alternating excess and arrest of development of the opposite divisions
of the trunk well illustrate the law of organic equivalents.

The appendages of the abdominal segments are developed, like
those of the thoracic ones, from the inferior arcs : they are usually
broad, flat, ciliated plates, which may sometimes aid in respiration,
are more commonly organs for swimming, form a temporary place
of attachment and protection to the ova, and are restricted to this
use in the females of the Brachyura, in which the abdomen or
tail is concealed by being bent forwards upon the sternum. In the
hermit crabs, which present an anomalous softness of their abdominal
segments, the last pair of appendages form the claspers by which the
parasite holds fast by the columella of the shell it may have selected
for its abode.

The calcified integument of the Crustacea being inelastic, inex-
tensile, and not endowed with inherent powers of growth ; being like-
wise so disposed in the Podophthalma, as to inclose and protect the
greater part of the body by a few large shield-like plates, must needs
be thrown off' to allow of the growth of the animal. This moult of
the external integument has been observed in a few species of Crus-
tacea to take place annually ; and a like ecdysis is probably common to
all the class. Reaumur has given the best account of the process
in the craw-fish {Astacus Jiuviatilis) . It takes place generally in the
month of August. The animal previously retires to some place of
concealment, is quiet and fasts for a few days, during which time the
old calcified epiderm is loosened from the corium by the formation of a
new membranous layer beneath. As this begins to harden, the animal
takes measures to rid itself of its old crust ; it rubs its legs against each
other, throws itself upon its back, contracts and swells out the body,
with alternate violent inflections and intervals of rest. The carapace is
thus separated from the abdominal segments, is pushed upwards, and
the animal liberates its head with the eyes and antennae, which are
provided with new sheaths : then the more diflficult operation of freeing
its extremities takes place, the old solid coverings of which split length-
wise, and are shaken off. Finally, the crawfish creeps out of the re-
mainder of its old shell by withdrawing the abdominal segments ;

M 4

168 LECTURE XIV.

when the parts of the cast-off shell frequently return so nearly to their
old positions as to represent the outward form of the animal with all
its appendages, even the hairs and lining of the stomach. In one or
two days the calcification of the new crust is completed, and the animal
is restored to health and activity. During this period two very re-
markable accumulations of calcareous matter, situated at the sides of
the stomach, and known in the old pharmaceutical works as " Oculi
Cancrorum," have disappeared : it would seem that the hardening
material had been previously accumulated in readiness for the rapid
calcification of the new crust, in order to reduce to the shortest period
the defenceless state of the craw-fish after its moult.

The Crustaceous Homogangliata are not less remarkable for
the different conditions of their nervous system, arising out of the
progressive concentration of its central masses, than for the diver-
sity of their outward forms. Even in the higher, or Malacostracous
division, a very extensive series of modifications are presented,
which lead from the Anellidous to the Brachyurous type, or that of
the crab.

In the lowest vermiform, isopodous, and isocyclous Crustacea, the
dermal skeleton has become sufficiently firm and resisting to enable
the trunk to be raised by the articulated members above the ground.
The muscular system attains a proportionate increase of volume and
force: so that when we contrast the conditions of the sensitive
integument and of the motor system in these Crustacea with those of
the same systems in the Anellides, we obtain most instructive tests of
the value of that hypothesis which ascribes sensation exclusively to
the ganglions, and the motive energy to the non-ganglionic nervous
columns of the Articulata. The same hypothesis will be more
severely tried by the comparative anatomy of the nervous system in
the higher species of the Crustacea, on account of the varying con-
ditions as to sensation and motion which different parts of their more
diversified forms of body present.

We find in the lowest Isopoda, as the woodlouse (Oniscus) and
the sandhopper (Talitrus), that the supposed sensitive organs, the
ganglions of the abdominal chords, are more developed than in the
highest Anellides : they are likewise more distinctly bilobed ; each
lateral chord presenting its own ganglionic enlargements, which are
in juxtaposition, but not confluent, so that there is a distinct pair of
ganglia for each segment. If these ganglions be microscopically
examined, three orders of nervous filaments may be distinctly per-
ceived in them. The first is longitudinal, and extends over the
dorsal aspect of the ganglia; the second is also longitudinal, and
originates from, and terminates in, the ganglia ; the third is trans-

CRUSTACEA. 169

verse, and connects the two ganglions of each pair with each other,
and with the transverse nerves. The Talitrus presents ten pairs of
nearly equidistant sub-abdominal ganglions, the two first and the two
last being most approximated. In the Cymotlioa {fig- 89.), a species
in which the tapering terminal segments of the body have begun to
be concentrated by longitudinal approximation, the corresponding
nervous ganglions at the posterior part of the abominal chord present
a corresponding change, advancing forwards like the caudal part of
the spinal column in the metamorphosed larva of the frog.

In the higher Crustacea, with a thorax covered by the cephalic
shield, and supporting disproportionately large and prehensile
anterior extremities, the thoracic ganglia exhibit proportionate
increase of size, with a tendency to unite, or with actual con-
fluence. The ganglions of each lateral abdominal chord have
now more completely coalesced by transverse approximation. In
the Squilla mantis, the supra-cesophageal ganglion or brain sends
off five nerves on each side, those to the long antennae being recurrent
in their course. Stomatogastric nerves arise from the oesophageal
chords, which unite below into a long sub-oesophageal ganglion,
apparently formed by a confluence of three originally distinct pairs.
This is succeeded by three other ganglions in the thorax, supplying
three pairs of thoracic legs ; and there are six ganglions in the mus-
cular tail.

The neurology of the Crustacea has been most completely illustrated
in those species which are covered by a dense insensible crust.
Succow, in 1818, and Brandt, in 1833, published excellent descrip-
tions of the nervous system of the Astacus fluviatilis {fig. 3. p. 13.).
The cephalic ganglion sends branches to the eyes, to the large and
small antennae, to the antennal sheaths, and to the organs of hearing.
A nearly straight chord is continued from this ganglion, on each side
of the oesophagus, to the first of the sub-abdominal series. An
azygous nerve arises from the middle of the posterior surface of the
cephalic ganglion, and passes backwards to the stomach, where it
communicates with two nerves given off one from each of the oeso-
phageal chords to supply the stomach. The sub-oesophageal ganglion
distributes nerves to the masticatory organs and to the pharynx, just
as the medulla oblongata sends off the fifth pair and glosso-pharyn-
geal in the vertebrate animals. The second to the sixth thoracic
ganglia inclusive, supply the feet and gills with nervous influence ;
the generative organs receive long filaments from the fourth, the
fifth, and the sixth thoracic ganglions. The ventral or sternal artery,
descending from the heart, passes between the nervous columns at
the interspace between the fourth and fifth ganglions. Six ganglions

170 LECTURE XIV.

are developed on the abdominal chords, which are continued along
the muscular tail : the last, which is above the anus, is the largest,
and radiates the nerves to the terminal swimming plates of the tail.
This is probably a coalescence of the originally distinct ganglions of
the sixth and seventh segments of the abdomen or tail.

The nervous system of the lobster is displayed in these dissections
by John Hunter* and Mr. Swan, in whose work on Comparative
Neurology it is beautifully illustrated. The nerves of the lobster
closely correspond with those of the fresh-water species, or craw-fish.
The non-ganglionic tracts are shown in this dissection of the lobster
by Mr. Newport f ; but the distinctions of the origins of the nerves
from the dorsal and the ventral tracts are, as Mr. Swan remarks, by
no means clear. The oesophageal columns are united in both species
of Astacus by a transverse commissural chord.

In the prawn (JPalemoTi) and rock-lobster {Palinurus)^ the thoracic
ganglia coalesce to form a long, elliptical, perforated nervous mass.
In this dissection of a hermit-crab (Pagurus)\^ the cephalic ganglion
presents a transversely quadrate form, and sends off the usual nerves
to the eyes, the ears, and the antennae. The lateral oesophageal
chords, after supplying the digestive system with the stomato-gastric
nerves, unite below to form the ganglion which distributes nerves to
the maxillary apparatus and pharynx. This is succeeded by a large
oblong ganglion, situated at the base of the great nippers, and of the
second pair of feet, both of which pairs it supplies. The lateral
chords diverge for the passage of the artery, re-unite to form a third
thoracic ganglion, smaller than the second, supplying the third pair
of thoracic legs, and sending off three pairs of nerves posteriorly. Of
these the lateral pair goes to the fourth diminutive pair of feet ; the me-
dian pair supplies the fifth feet : the two remaining dorsal nerves, which
are of minute size, form the continuations of the abdominal chords,
and pass along the under or concave side of the soft, membranous, and
highly sensitive abdomen to the anus, anterior to which the last small
ganglion is situated; this supplies the nerves to the muscles of the
caudal plates, here converted into claspers, and enabling the animal
to adhere to the columella of the univalve shell, which it may have
selected to protect that portion of its body which nature has left
undefended by the usual dense and insensible crustaceous covering.

Experiments have been made, and repeated, in order to determine
whether the ganglionic portions of the abdominal chords of the
Artieulata have the same restricted function which the posterior

» Preps. Nos. 1301, 1302, 1303. f Prep. No. 1302, A.

\ Prep. No. 1303. B.

CRUSTACEA. 171

roots of the spinal nerves in the Vertehrata have been proved to
possess. With respect to the anatomical grounds which were first
adduced in proof of this correspondence of function, they are in-
validated by the fact that the presence of ganglions in the sensitive
roots of the spinal nerves is not their constant character.

The results of the experiments alluded to, though somewhat con-
tradictory, are, upon the whole, as might have been anticipated,
hostile to the conclusions founded upon a partial anatomical analogy.
A more extended investigation of the Comparative Anatomy of the
Nervous System has remedied the imperfections of the experimental
inquiry, has supplied the answers which were in vain attempted to be
gained by mutilating the living Crustacea, and has brought the hy-
pothesis in question to the test of deductions which may be legitimately
drawn from those surer experiments which Nature herself has left
for our instruction in the modifications of the crustaceous type of struc-
ture. We have here * two opposite conditions of a large and important
part of the trunk of two nearly allied Crustacea. In the lobster {As-
tacus) the abdomen or tail is encased in a series of calcareous rings,
forming a hard and insensible chain armour : but in the same degree
as sensibility is lost, motility is acquired ; a great proportion of the
muscular system of the animal is concentrated in the tail, which
forms its most powerful and almost exclusive organ of swimming.
In the hermit-crab {Pagurus), on the other hand, the muscular system
is almost abrogated in the long abdomen ; for this, in fact, takes no
share in the locomotive functions of the body : it is occupied by part
of the alimentary canal, and by glandular organs : the sensibility of the
external integument is not impaired or destroyed by the deposition
of calcareous particles in its tissue ; but it retains the necessary
faculty of testing the smooth and unirritating condition of the inner
surface of the deserted shell, which the animal chooses for its abode :
minute acetabula are developed in groups upon this sensitive in-
tegument f, to which, also, delicate ciliated processes are attached.
The muscular system is reduced to a few minute fasciculi of fibres
regulating the action of the small terminal claspers. Now, if, as has
been conjectured, the ganglionic enlargements of the abdominal chords
monopolise the sensorial functions, and the non-ganglionic tracts the
motor powers, we ought to find the nerves, which supply the muscles
of a tail constructed almost exclusively for locomotion, to be de-
rived from non-ganglionic columns ; whilst in the tail, which is almost
as exclusively sensitive^ the ganglions ought to have been large and
numer,ous, for the supply of nerves to the integument. The contrary,

* Preps. Nos. 130]. and 1303. B. f Broderip, Zool. Journ. vol. iv. p. 200.

172

LECTURE XIV.

however, is the fact ; six well developed ganglions distribute nerves to
the muscular fibres of the lobster's tail ; non-ganglionic columns supply
the sensitive tail of the hermit-crab. One ganglion, indeed, is present
in the Pagurus, but both its situation and office alike militate against
the hypothesis of its special subserviency to sensation : it is developed
upon the end of the smooth abdominal chords, and seems to have
been called into existence solely to regulate the actions of the muscles
of the claspers by which the hermit keeps firm hold of the columella
of its borrowed dwelling.

The general progress of the development of the nervous system in
the Crustacea has been, as we have seen, attended with increased
size, and diminished numbers of its central or ganglionic nerves.
The divisions of each pair of ganglia first coalesce by transverse
approximation : distinct pairs of ganglia approximate longitudinally,
conjoining as usual from behind forwards : confluent groups of ganglia
are next found in definite parts of the body, as on the thorax of
those species which have special developments and uses for par-
ticular legs. In the crab, in which the general form of the body
attains its most compact form (^fig- 90.), the ventral nervous trunks

are concentrated into
one large oval gan-
glion(^), from which
the nerves radiate to
all parts of the trunk,
the legs, and the
short tail.

This condition of
the nervous system
has been described
by Cuvier in the
common crab, and
is illustrated by Mr,
Swan's dissections,
from which his beau-
tiful plates have been
taken. The corre-
sponding structure of the nervous system is also well displayed by
Audouin and Edwards in the Maia. x\n analogous concentration of the
nervous system, but with interesting modifications, has been described
by Professor Van der Hoeven*, in the Zzm2^7w5 or King-crab, the
most gigantic form of the Entomostracous tribe, and probably the

Cancer.

Recherches sur I'Anat. des Limules. Fol. 1838.

CRUSTACEA. 173

only existing genus from which we may derive an insight into the
organisation of the extinct Trilobitic Crustaceans. This considera-
tion has induced me to select for the exercise of the peculiar skill of
Mr. Goadby, our anatomical assistant, the well preserved specimens
o^Liniulus for which the College is indebted to Mr. Boott of Boston,
U. S. In these beautiful dissections by Mr. Goadby, the details of
the nervous system are clearly displayed, and will, with the rest of
the Anatomy of the Limulus, be published by the Council of the
College.

Three principal divisions of the nervous system of the Crustacea may
be defined according to the views which I entertain of their functions.
Thus, admitting, from analogy, that the supra-oesophageal ganglionic
centre {Jigs. 89. and 90. c) is that in which true sensation and volition
reside, then those nervous filaments which are exclusively connected
therewith, and some of which would seem to extend the whole length
of the animal along the dorsal aspect of the ganglionic columns, would
form with their ganglionic centre the true sensori-volitional system ;
whilst any other ganglions superadded to the abdominal columns,
with the nervous filaments terminating in or originating from them,
would constitute the system for the automatic reception and reflection
of stimuli. The stomato-gastric nerves, connected partly with the
brain and partly with the oesophageal columns, will form a third
system analogous to the great sympathetic or organic nerves of the
Vertebrata. In these views I coincide with the ingenious physiologist,
Dr. Carpenter, and shall feel happy if their accuracy and soundness
have received any additional proof from the facts of Comparative
Anatomy, which, in the Hunterian Lectures of 1842, were for the
first time brought to bear upon this interesting problem.

The sense of touch can be but very feebly exercised by the com-
mon integument of the Crustacea, can hardly, indeed, exist except in
those parts of the surface of the body which remains soft and un-
defended by the hard crust, such as the joints of the under part of
the body, and the surface of the soft tail in the hermit crabs. The
fine hairs which project from many parts of the integument may
compensate for its low endowment of the tactile sense ; the two pairs
of jointed antennse {fig- 90. a) are instruments fitted for the most
delicate exploration ; and the smaller but similar organs attached
to the jaws, and called palpi, may also receive some impressions
analogous to those of savour or smell. The Crustacea have no true
tongue, but the sensations of the membrane lining the interior of
the mouth and the oesophagus may guide them in the selection which
they make of objects of food.

The sense of hearing is referred to a cavity with a round orifice

174 LECTURE XIV.

closed by a membrane, excavated in the first joint of the second pair
of antennae, in the lobster and other Macroiira. In most of the
Brachiura the membrane is stated by Dr. Edwards to be replaced by
a small moveable calcareous disc, which is pierced with a small oval
opening, over which there is stretched a thin and elastic membrane.
The external opening of the ear is closed by this bony disc, A
second small plate is so situated as to regulate the tension of the
auditory membrane, whilst the rigid stem of the antennae, in which
the whole organ is situated, is well adapted to render the auditory
vibrations more distinctly perceptible. These vibrations are con-
veyed through the medium of a vesicle filled with fluid to a branch
of the antennal nerve which expands in the vesicle.

With respect to the organ of vision, we find in the class Crustacea a
most extensive and interesting series of gradations, leading from the
sessile median eye-speck to two distinct eyes, provided with all the
essential optical apparatus and placed upon moveable peduncles. Ocelli
or stemmata are combined with compound eyes in the same species
in certain Entomostracans, as Apus and Limulus. A transparent
speck of the integument forms the cornea of the ocellus, immediately
behind which there is a spherical crystalline body in contact with a
gelatinous or vitreous humour, upon which the extremity of the optic
nerve expands : a layer of dark pigmentum covers all these parts with
the exception of the cornea. In the compound eyes of Daphnia, the
smooth undivided cornea protects and transmits the rays of light to
an aggregation of small ocelli, each of which is lodged in a pigmental
cell : the similarly constructed compound eye of the active little
Branchipus is supported on a short moveable peduncle.

The large lateral compound eyes of the Limulus are sessile ; the
cornea is divided into a considerable number of small circular facets,
each of which corresponds to an ocellus ; and the optic nerve, after its
long course as a simple chord, divides near the eye into a pencil of
fine filaments, which severally receive the impressions from their re-
spective ocelli, of the aggregate of which the large lateral eye is com-
posed : the two small simple median eyes, which are almost in contact,
command the space before the head, which is out of the range of the
large compound eyes. Each simple eye receives its distinct nerve
from the anterior apex of the corresponding cerebral lobe.

In the sessile eyes of the Edriophthalma^ as, for example, in the
Serolis, the inner layer only of the cornea is divided into hexagonal
facets, corresponding with the number of the conical crystalline
lenses of the compound eye. But in the Trilobites, the cornea pre-
sents the same subdivided surface as in the Limulus ; and the position
of the two eyes agrees with that of the corresponding compound pair

CRUSTACEA. 175

in the large existing Entomostracan. The eyes are more elevated in
the Trilobites. In the Asaphus caudatus the cornea is divided into
at least 400 compartments, each supporting a circular prominence :
its general form is that of the frustum of a cone incomplete towards
the middle line of the head, but commanding so much of the horizon
in other directions^, that where the distinct vision of one eye ceases^, that
of the other begins. In the mandibulate Crustaceans, distinguished
by having their compound eyes supported on moveable peduncles, the
form of the corneal facets varies ; they are square in the river craw-fish,
hexagonal in the hermit and common crabs. There is a conical crystal-
line lens behind each facet imbedded in a small vitreous humour, upon
which the optic filament expands, and each ocellus is lodged in a pig-
mental cell, which likewise covers the bulb of the optic nerve; the cavity
containing the compound eye is closed behind by a membrane contin-
uous with the inner layer of epiderm, and pierced for the passage of
the optic nerve {fig^ 90. e). In the Podophthalmous Crustacea there
is generally a spacious furrow or cavity, in which the eye and its
peduncle can be lodged and protected, and it is termed the orbit. In
one or two species the eye-stalks project beyond the margins of the
carapace.

One of the most valuable and interesting results of the study of
the comparative anatomy of the eye in the Crustacea is the insight
which the fossilised remains of similarly constructed organs of vision
in the extinct Crustacea have given respecting the state of the world
at the time when they existed ; and I cannot better conclude the pre-
sent discourse than in the eloquent language of the geologist who
first taught the value of the evidence in question. The eyes of the
Trilobites of the transition rocks, and those of their nearest congeners,
the fossil Limuli from the Carboniferous series, " give information,"
says Dr. Buckland, " regarding the condition of the ancient sea and
ancient atmosphere, and the relations of both these media to light, at
the remote period when the earliest marine animals were furnished
with instruments of vision in which the minute optical adaptations
were the same that impart the perception of light to Crustaceans now
living at the bottom of the sea.

" With respect to the waters wherein the Trilobites maintained
their existence throughout the entire period of the transition formation,
we conclude that they could not have been that imaginary turbid and
compound chaotic fluid, from the precipitates of which some geologists
have supposed the matei'ials of the surface of the earth to be derived ;
because the structure of the eyes of these animals is such, that any
kind of fluid in which they could have been sufficient at the bottom,
must have been pure and transparent enough to allow the passage of

176 LECTURE XV.

light to organs of vision, the nature of which is so fully disclosed by
the state of perfection in which they are preserved. With regard to
the atmosphere, also, we infer that had it differed materially from its
actual condition, it might have so far affected the rays of light, that
a corresponding difference from the eyes of existing Crustaceans
would have been found in the organs on which the impressions of
such rays were then received.

" Regarding light itself, also^ we learn, from the resemblance of
these most ancient organisations to existing eyes, that the mutual
relations of light to the eye, and of the eye to light, were the same
at the time when Crustaceans, endowed with the faculty of vision,
were first placed at the bottom of the primeval seas, as at the pre-
sent moment.

" Thus we find among the earliest organic remains, an optical in-
strument of most curious construction, adapted to produce vision of
a peculiar kind, in the then existing representatives of one great class
in the articulated division of the Animal Kingdom. We do not find
this instrument passing onwards, as it were, through a series of ex-
perimental changes from more simple into more complex forms ; it
was created at the very first, in the fulness of perfect adaptation to
the uses and condition of the class of creatures to which this kind of
eye has ever been, and is still, appropriate."

LECTUEE XV.

CRUSTACEA.

The Limuli, which form the only genus of large Crustaceans repre-
sented by species which co-existed with the Trilobites, differ from all
other living Crustacea in their organs of mastication, which are the
modified basal joints of the five posterior pairs of legs : the first
small pair serve to bring the objects of food to the mouth ; they are
supported on a rudimental labrum. In the Asaphus platycephalus Mr.
Stokes has discovered a distinct subquadrate labrum deeply emar-
ginate anteriorly; the nearest approach to this, the only known part
of the trophi of the Trilobites, seems to be made by the entomostra-
cous genus Apus, in which, however, the labrum is truncated. A
few of the lowest organised Crustacea, as Caligus, Nymphon, and
Pycnogonoiiy obtain their aliment, like the Epizoa, by suction.

In the Malacostracous Crustacea the mouth is closed by a small and

CRUSTACEA. 177

simple membranous labrum above, by a bifid labium below, and by a
pair of maxillae and mandibles at the sides ; the mandibles are the
legs or jointed appendages of the fourth cephalic segment. In the
common crab you will observe behind and exterior to the mandibles
a second pair of jaws, which, like the first, have their principal part
terminated by a cutting edge : the two following pairs of jaws are dis-
tinguished by their articulated feeler or palp, and by their fiabelliform
appendages, which penetrate into the interior of the branchial cavity ;
the maxillary plate is armed with teeth : the fifth and last pair of
jaws has the maxillary plate so much expanded as to cover and protect
the whole oral apparatus : it has likewise a palp and flagellum articu-
lated to its base. All the foregoing maxillary organs are modifications
of entire limbs, which are thereby translated from the locomotive
series ; the jointed legs so metamorphosed belong to the last four
cephalic, and the first two thoracic, segments.

The alimentary canal is most simple in the suctorial Crustacea, in
which it presents no noticeable difference from that in the Epizoa;
the hepatic appendages are however more localised and better de-
veloped.

In the Liraulus the mouth is situated nearly in the centre of the
inferior surface of the great cephalo-thoracic segment ; the oesopha-
gus is continued from it in a very unusual course forwards, and ex-
pands into a stomach, which is situated at the anterior part of the
head. This organ is abruptly bent upon itself upwards and back-
wards, and is continued by a gradual diminution of diameter, as ap-
pears upon an external view, into the intestine, which passes back-
wards with a slight vertical bend, to the base of the penultimate ab-
dominal segment. When we examine the interior of the alimentary
tract, the distinction between the stomach and intestine is effected, as
Van der Hoeven has shown, by a conical valvular pylorus, which
projects into the commencement of the intestine. The stomach is
lined by a very dense and corrugated horny membrane. The hepatic
mass, which, with the generative glands, fills the greater part of the
cephalo-thoracic cavity, pours its secretion into the commencement
of the intestine by two ducts on each side.*

In the Stomapods or Squillae the stomach also bends forwards in
advance of the cardiac orifice ; a bi-articulate plate extends from
that orifice backwards, through the pylorus into the intestine, and
regulates the passage of the alimentary substances into that tube ; they
are previously subjected to the action of four lateral dentated pyloric
processes.

In the higher Crustacea the stomach is of a globular form, more
* Prep. No. 477, A.
N

178 LECTUKE XV.

capacious than in tlie Lwmlus, and its walls are connected with a
calcareous frame-work supporting dense tubercles, which project into
the interior of the stomach around the pylorus, and are so situated
and moved with relation to each other as to divide and bruise the
alimentary matter before they pass into the intestine. In the com-
mon lobster these gastric teeth are three in number, the middle one
serving as a kind of anvil upon which the two larger lateral pieces
work.* This complex kind of gizzard is sometimes found to be
everted and protruded from the mouth, the gastric teeth being then
external, like those of the anterior muscular segment or proboscis of
the alimentary eanal in the Anellides.

The intestine in all the Crustacea is continued to the vent without
convolutions ; a terminal portion or rectum is sometimes, as in the
lobster, indicated by a slight circular valve ; the vent is situated
beneath the terminal segment of the abdomen, anterior to its appended
swimming plates in the Macroura, which would indicate that the
long spinal appendage of the Xiphosura was not the analogue of the
post-abdomen, but of its last joint in the Macroura.

The liver is a considerable organ in all the Crustacea ; it makes its
appearance in the inferior species as so many caecal prolongations of
the intestine, continued from many points, according to the primitive
form which it presents in the Aphrodita. The biliary caeca extend
even into the limbs in the Nymphons. In the Stomapods the biliary
caeca, continued ten or eleven in number at equidistant points from
each side of the intestine, are more ramified, and are confined to the
thoracic-abdominal cavity, where they penetrate the interspaces of
the muscles, f

In the Decapod Crustacea the liver consists of two symmetrical
halves, communicating by distinct ducts with the intestine; each
half consists of numerous lobes, which, in the larger Macroura and
Brachyura, are leaf-shaped, and composed of straight tubular caeca,
arranged obliquely to a median canal, which forms, as it were, the leaf
stalk. In some species one or two pairs of long slender and simple
tubuli likewise communicate with the intestine.

No other vessels are yet known to convey the chyle or nutrient
fluid to the circulating system than the irregular venous receptacles
which are in contact with the parietes of the intestine. Almost the
whole venous system presents the form of m ide flattened sinuses, and
offers an intermediate condition between that in the Nereis and the
generally diff^used state of the venous blood through all the cellular
interspaces of the body in the class of insects. Through these
sinuses, however, the blood flows in a constant and definite course.

* Preps. Nos. 407, 408. f Duvcrnoy, Annales des Sciences, vi.

CRUSTACEA. 179

The numerous experiments of Audouin and Milne Edwards * on
the circulation of the Crustacea, and the apparently favourable cir-
cumstances under which they were made, have very generally been
regarded as conclusive of the accuracy of their explanation of that
important function in the present class. According to these physio-
logists no other than the two great branchial veins terminate in the
heart, and, consequently, only pure aerated or arterial blood is pro-
pelled by it over the general system : the circulation is, in fact, the
same as in the Gasteropodous Mollusca : the ventricle is exclusively
systemic, and is provided with only two venous apertures. Four
such apertures are described and figured by Dr. Lund on the dorsal
surface of the heart, but these are regarded by Audouin and Ed-
wards as depressions merely between the muscular fasciculi, having no
communication with the ventricular cavity.

I have tested the conflicting evidence of these observers by dissec-
tion of the heart in the lobster ; and you will perceive by this prepa-
ration -|- that it is more complicated than even the Danish Naturalist
supposed, and fully bears out the opinion of Hunter in regard to the
mixed nature of the circulation in the Crustacea.

Fig. 91. shows the heart laid open on the ventral aspect ; by ex-
posing its cavity from this side, it was read-
ily determined whether the exterior de-
pression on the dorsal surface did or did
not lead into the cavity. On either side of
the anterior depression from which the two
antennal(/) and the ophthalmic (^) arteries
arise, there is a large oblique fissure, guarded
by a pair of semilunar valves. The vein^
which terminates by each of these orifices,
is an extended, irregular, and extremely
flattened sinus, lying above the heart, and
between it and the lining membrane of
AstacusLrinus. ^^^ ^^^^11, communicating anteriorly with a

similar broad irregular flattened sinus,
which occupies a similar situation above the stomach, and receiving
posteriorly the blood from a series of flat and expanded sinuses which
correspond to each segment of the tail. There are two similar
openings at the sides of the ventricle, posterior to the preceding,
which conduct the blood from lateral sinuses into the heart : these
orifices, indicated by the bristles (c, c), have each a pair of semilunar
valves. The arterial blood, returned from the branchiae, enters the

* Hist. Nat. des Crustaces. 1829 t No. 898. A.

N 2

180 LECTURE XV.

heart by the large orifices on the sides of the ventral aspect {d, d),
regurgitation being likewise prevented by two semilunar valves at each
orifice.

The muscular fasciculi of the ventricle are so arranged as to leave
tolerably distinct chambers for each series of arterial orifices. The
strongest bands or columns are transverse, and dorsad of the branchial
apertures : anterior to these is a chamber receiving the carbonized
blood from the two anterior dorsal apertures ; it is partially divided,
the upper chamber giving off (/) the ophthalmic, and (g) the anten-
nal arteries. The lower chamber sends off (^, k) the hepatic arteries.
The larger posterior chamber receives the two lateral venous aper-
tures, and gives off (h) the superior caudal artery, and (i) the sternal
artery, the only one which has a pair of semilunar valves at its origin.

A portion only of the ordinary venous blood is returned directly
by the four valvular orifices just described. The blood is returned
from the maxillae and legs to a series of inferior lateral sinuses at the
bases of the branchiae ; from these sinuses it passes, by vessels per-
forming the office of branchial arteries along the outer margin of the
gill, and after being distributed over the branchial lamellae, is collected
into the vein along the inner margin of the gill, and by the union of
the branchial veins into one trunk, on each side, is poured into the
ventricle by the two orifices on its under surface (d, d).

We may trace in the heart of the Crustacea a gradational series of
forms, from the elongated median dorsal vessel to the shorty broad,
and compact muscular ventricle in the lobster and the crab. In
all the Crustacea, as in all the other articulate animals, the heart
is situated immediately beneath the skin of the back, above the
intestinal tube, and is retained in situ by lateral pyramidal muscles
(Jig. 91, a, a). In the lower, elongated, slender, many-jointed
species of the Edriophthalmous Crustacea the heart presents its vasi-
form character : it is broadest and most compact in the crab.

In this series we may trace a general correspondence in the pro-
gressive development of the vascular as of the nervous system, con-
comitant with the concentration of the external segments, and the
progressive compactness in the form of the entire body. But there
is a remarkable exception to this concomitant progress in the Limulus,
indicative, with the general condition of the instruments of locomo-
tion and respiration, of the essentially inferior grade of organisation
of that genus, which, as has already been observed, seems to be the
last remnant of the once extensive group of Trilobitic Crustacea,
which swarmed in the seas of the ancient secondary periods of the
earth's history.

We have seen in the compact and broad existing representative of

CRUSTACEA. 181

those extinct gigantic Entomostracans, that the nervous system ex-
hibits a concentration of its principal central mass around the mouth,
analogous to its condition in the common crab, but with a gan-
glionic double cord continuing from it. The heart, however, is
far from presenting a corresponding degree of concentration : it
remains an elongated, fusiform tube, extending parallel with the
intestine from the pylorus to the rectum : it is contained in a peri-
cardium with thin membranous walls, formed by the central sinus
of the venous system, and it receives the blood from that sinus
and from the branchial veins by a series of from seven to ten lateral
vertical slits, defended by valves as in the higher Crustacea. * An
aortic trunk proceeds from each extremity of this heart. The an-
terior aorta is the largest, and immediately divides into three branches.
The middle and smallest branch passes forwards to the anterior edge
of the cephalic shield, following the curve of its middle line, and sup-
plying the small median ocelli in its course. The two larger lateral
branches form arches which curve down the side of the stomach and
the oesophagus, giving branches to both those parts and to the intes-
tine, and becoming intimately united with the neurilemma of the
oesophageal nervous collar. They unite at the posterior part of that
collar, and form a single vessel, which accompanies the abdominal
nervous ganglionic chord to its posterior bifurcation where the vessel
agaiu divides. Throughout all this course the arterial is so closely
connected with the nervous system as to be scarcely separable or dis-
tinguishable from it. The branches of the arterial and nervous trunks
which accompany each other may be defined and studied apart.

The posterior aorta is chiefly destined for the supply of the sword-
like tail of the Limulus : the first part of its course is wavy, to adapt
it to the strong inflections of that appendage. The aerated is mixed
with the venous blood in the heart, and is propelled in that mixed
condition throughout the body in the Limulus, as in the lobster.

The respiratory organs in the Crustacea are essentially appendages
to the basal articulations of a certain number of the feet, and are ori-
ginally developed from the flabelliform appendage, although they ulti-
mately become entirely distinct from the extremities in the higher
Crustacea.

The Branchiopods are so called because their fins or feet present
the form of simple plates or flattened vesicles, which float in the
surrounding fluid, and expose the blood to the oxygen which the
water contains. The branchia are appended to the thoracic limbs,
in the form of membranous plates, in the Amphjpoda ; and to the ab-

* Van der Hoeven, loc. cit. pi. 2. fig. 9.

N 3

182 LECTURE XV.

dominal limbs, as subdivided lamellae, in the Isopoda : the branchial
plates expand into vesicles attached to the thoracic feet in the Lcemo-
dipoda. In the Stomapoda, the respirator}^ plates are also external,
and are appendages of distinct locomotive organs, and each plate is
divided into a series of small filaments or tubes ; so as to resemble a
broad feather : their position is abdominal. Similarly formed ex-
ternal gills are appended to the thoracic segments in the Thysanopoda.
In the lobster and crab tribes, the branchiae are protected by the
carapace, and are lodged in lateral recesses formed by the apodemata
of the thoracic segments. These branchial recesses are parts of a
common cavity, lined by an internal fold of the tegumentary mem-
brane, and having two apertures of communication with the sur-
rounding medium. The posterior aperture lets in the water, which,
traversing the branchial cavity _, escapes by the one in front. In the
crabs the entry is a cleft in front of the base of the chelae or forceps-
claw, and is so placed in reference to the prolonged base of that limb
as to be closed or opened at the will of the animal. In the lobster
and other Macroura, the entry to the branchial chamber is an extended
fissure.

The dynamical part of the respiratory functions is performed by
the lamelliform appendages of the second pair of jaws, which are so
situated in regard to the outlets of the branchial chambers as to drive
out a certain quantity of the water which has been admitted into the
chamber. * The loss of the foul water necessitates the entry of fresh
water by the inferent orifices ; the respiratory cavity being neither ca-
pable of expansion nor contraction. The mode of breathing in the
crypto-branchiate or decapod Crustacea is thus the reverse of that in the
Batrachia, in which the dynamical mechanism serves only to draw in
the respiratory medium in successive quantities. In the higher verte-
brata the thorax is so constructed as to execute acts both of inspiration
and expiration.

The branchiae in the decapod Crustacea are in the form of long
and slender quadrangular pyramids, and consist of either numerous
thin plates, or minute cylinders closely arranged perpendicular to the
axis of the pyramid. There are nine branchial pyramids on each side
in the crabs, two being rudimental ; but the number is more variable,
and usually greater, in the Macroura, amounting to twenty-two in the
lobster.

So far as the"gills are attached to the bases of the ambulatory or nata-
tory legs, they must be influenced by their movements ; and the more
active the progress of the Crustacean, the more briskly will its respi-

* Milne Edwards, Annales des Sciences Nat. torn. xi.

CRUSTACEA. 183

ration proceed ; and since the muscular energy directly depends upon
the amount of respiration, the two functions are brought into direct
relation with each other by this simple connection of their respective
instruments.

The land crabs have their branchiae always supported by water
through special modifications of the apertures of the branchial cavities,
which enable them the better to retain fluid, and also by numerous
folds or by a spongy structure of the lining membrane of the respira-
tory cavity by which the quantity of the contained fluid may be aug-
mented. The moisture contained in the branchial chambers of the
land-crabs ( Gecarcinus) and tree-crabs (^Birgus) is doubtless much
more highly aerated than the water which bathes the branchiae of
the strictly aquatic species, and thus may explain the fact that the
Crustacea -which habitually live out of water are drowned by
being long immersed in that fluid.

No other trace of distinct excretory organs has hitherto been
detected in the present class than the simple, unbranched, long, and,
slender tubes which open into the intestinal canal of some of the higher
Crustaceans : these may be uriniferous tubes, like the corresponding
parts in certain insects and spiders.

Tenacity of life in the Crustacea appears not to be enjoyed in any
unusual degree : but some species, as the Artemia salina, can exist
in hot and strong brine^ which would quickly destroy most other
animals.

Like other Articulata subject to periodical ecdysis, the Crustacea
have the power of reproducing lost extremities. If a leg be fractured
or severed across one of its segments, it is cast oflf by a violent
muscular effort at the second articulation : if the Crustacean have
not the power of thus ridding itself of the wounded member, it
usually dies from the haemorrhage ; but this is immediately ar-
rested by the contraction of the lacerated part of the joint where
the limb is cast off" with least difliculty and pain. A small
cylindrical appendage first sprouts from the cicatrix, which soon after
presents distinct articulations, and resembles in miniature the limb
which it is destined to replace : its growth is slow until the period of
the moult, when, if the animal be in vigorous health, the new member
rapidly acquires its normal size.

There is no propagation by spontaneous fission or gemmation in the
class Crustacea : every species is developed from ova formed by organs
peculiar to one series of individuals, and impregnated by the fertilising
product of organs as peculiar to another series. But although the
male and female organs are never naturally combined in the same in-
dividual, accidental or monstrous hermaphrodites occasionally occur,

N 4

184 LECTURE XV.

in which the male organ is developed on one side, and the female organ
on the other side of the same animal. This dimidiate hermaphro-
ditism *, as it is termed, has been most commonly observed in the
lobster, and is indicated by external characters. The generative ori-
fices open on the last thoracic leg on the male side, in which the ab-
dominal plates are smaller and more simple; whilst on the opposite side
they are broader and more ciliated, and the generative aperture is situ-
ated on the middle or third ambulatory leg.

This singular kind of malformation seems to depend upon the very
slight connection, or want of connection, between the right and left
generative organs of the same individual, whether male or female.
The external apertures are always distinct on each side ; and when a
combination of the right and left generative organs does occur, it is
by a partial union of the two testes, or of the two ovaria.

In the male Cymothoa both the essential and efferent portions of
the male apparatus are distinct on each side : the testis is here much
simplified, and consists of three elongated pyriform vesicles forming
a common tube by the union of the short vasa deferentia, which arise
respectively from the great end of each vesicle.

In the Astacus fluviatilis the testes are blended together at the
middle line along the posterior half of their extent, anterior to which
they are separated and symmetrical : they consist of packets of mi-
nute contorted capillary secerning tubes. The vasa deferentia quit
the gland at the junction of its three apparent lobes : they form many
convolutions at the sides of the hinder part of the thoracic segment,
where they may be distinguished by their opake white colour. They
dilate into sperm receptacles in the last portion of their course, and
terminate at the small prominent orifices at the basal joints of the last
pair of thoracic legs.

In the Maia the testis consists of an elongated and convoluted mass
of extremely minute vermicular tubuli, which mass is united by a
slender transverse commissural process with the testis of the opposite
side. The vas deferens is formed by the gradual enlargement of the
tubuli, and is disposed in a number of close convolutions, and some-
what suddenly dilates into a spiral seminal receptacle, which ter-
minates, as in the Astacus^ on the basilar piece of the last pair of legs.
In many crabs, however, as in the Grapsus and Ocipoda, the external
opening of the male organ is found on the sternal part of the last tho-
racic ring. The terminal part of the duct can be everted by a kind
of erection to form a temporary organ of intromission; and the
Crustacea are singularly analogous to serpents in the double number

* Sec Brande's Diet, of Science, Art. HERMArHRODiTE,

CRUSTACEA. 185

as well as the structure of this part. Certain appendages of
the first and second abdominal rings in the male crabs are probably-
connected as exciting organs with the sexual function.

The female organs present, like the male, a progressive compli-
cation of structure as the species ascend in the class. Most of the
small Entomostraca carry the impregnated ova in appended ovisacs,
like those of the Lerneae. These sacs are not developed in the Lim-
ulus, which also differs from the smaller Entomostraca, inasmuch as
the ovarian mass interblends its lobes and processes with those of the
liver ; the oviducts form more frequent communications with each
other than in the higher Crustacea, but ultimately terminate, like the
vasa deferentia, by two distinct but continuous orifices on the back
part of the first abdominal lamelliform appendage.

The ovaria in the lobster are of great length on each side ; the
oviduct comes off from the outer part of nearly the middle of the
gland, and descends to terminate at the basal joint of the third pair
of ambulatory feet.*

In the Brachyura the female apparatus reaches its highest state of
complication, and consists of an ovary, oviduct, and a copulatory
pouch, or spermatheca, on each side. The ovaria are elongated
cylindrical sacs in the Maia, and are divided into an anterior and a
posterior part, the short oviduct being continued from the union of
the two : the anterior parts of the ovaria are united together by a
short transverse canal; the posterior divisions are very intimately
united through half their extent: the spermatheca is developed a
little above the termination of each oviduct.

The species of a genus of Macroura (3Ii/sis) are called " Opossum
shrimps," from carrying their ova during the process of development
in abdominal recesses, analogous to the marsupial pouch ; but this
superadded complexity in the reproductive economy is common,
under various modifications_, to all the Crustacea.

The ova, after extrusion from the oviducts, are retained and pro-
tected in the Cymoihoa and other sessile-eyed Malacostraca under
their thorax by means of the flabelliform appendages of the ex-
tremities, which appendages are unusually expanded, and overlap
each other, so as to form a marsupial cavity or temporary receptacle,
in which the incubation of the ova is completed. In the Podoph-
thalma, the lamelliform ciliated appendages of the abdominal seg-
ments include similar marsupial or incubatory recesses for the ova.
The female lobster and other Macroura are distinguished from the
male by the greater development of these appendages; and in the

* Prep. No. 3188.

186 LECTURE XV.

Brachyura the shorter abdomen or tail is so much more expanded in
the females as to cover the whole sternum, and render the sex dis-
tinguishable at a glance.

In certain parasitic species of Cymothoa, the males have eyes, the
females, which are considerably larger, have no eyes : they have pro-
bably been effaced by age and lack of use, as in the parasitic females
of the Epizoa.

The lower forms of Entomostracous Crustacea, and especially the
suctorial species, have long been known to undergo remarkable
changes of form in repeated moultings during their growth, analogous
to the metamorphoses w^hich have already been described in the
Epizoa : differing, in fact, from these only in degree ; the last or
procreative stage being attained in most Entomostraca under a
locomotive form, which differs less from that of the newly excluded
young, than does the corresponding mature stage of the deformed
parasitic Lernaea. There is a period when the young Eiraulus is
destitute of the characteristic caudal spine : this fact was first observed
by M. Edwards in the embryos on the point of exclusion from the
e.gg, at which period the abdomen supports only three pairs of ap-
pendages.

With respect to the Malacostraca^ in 1778, a Dutch naturalist.
Slabber, described and figured a minute swimming Crustacean of the
genus called Zoea by modern naturalists : it w as provided with a
pair of large and distinct eyes ; its carapace was armed with a long
frontal and a dorsal spine ; and its abdomen was terminated by a
forked tail. He preserved this little animal alive in sea water, which
was daily renewed, and on the fourth day he found that the animal
had changed its form; the feet, eyes, and antennae were more
developed, the frontal spine had become comparatively small, the
dorsal one had disappeared, and the tail had changed from the
bifurcate to the spatulate form, and was fringed by a row of short
spines. Many years elapsed ere this observation was repeated, and it
seems to have been forgotten, when Dr. Leach, the most accomplished
Crustaceologist of his day, founded the principal character of the
class Crustacea on the absence of metamorphosis.

During the spring of 1822, Mr. V. Thompson * captured an abun-
dance of the singular Zoeas in the harbour of Cove ; the largest of them
was daily supplied with fresh sea-water from May l^th until the 15th
of June, when it died in the act of changing its skin. The disengaged
members, invested with the new integuments, were changed both in
number and form, and corresponded with those of the decapod
Crustacea, the anterior pair being furnished with large pincers. Here,
therefore, was a strong indication that, under the form of a Zoea, was

* Zoological Ilcscarchcs, vol. i. Part I, p. 1.

CRUSTACEA. 187

masked that of some one or other of the higher Crustacea ; and, pro-
bably, one of the common species of the Irish coast. To the de-
velopment of these, therefore. Dr. Thompson next turned his attention,
and he succeeded in hatching the ova of the common crab during the
month of June, and found that the young were excluded under the
form of the Zoea Taurus^ with the addition of lateral spines to the
thorax ; whereupon he concluded that the decapod Crustacea indis-
putably underwent a metamorphosis.

In the year 1829 Dr. Rathke published his Researches on the river
craw-fish {Astacus fiuviatilis). In this species the ovum first appears
in the shape of a minute transparent vesicle, which afterwards becomes
surrounded by a second, forming the membrana vitelli : the nature of
the processes effecting this stage appears not to have been observed.
The yolk increases in quantity, and is rendered opake by the presence
of numerous granules, and changes from the lenticular to the spherical
figure ; then the internal minute transparent germinal vesicle quits
the centre, and comes into contact with one part of the parietes of
the ovum. The colour of the yolk successively changes to yellow,
orange, and brown ; the clear vesicle disappears, and the production
of the embryo commences. Rathke failed to ascertain what became
of the vesicle. The formation of the ovum in the ovary continues
half a year. In the month of November the vesicle was visible ; in
the ensuing March it had disappeared.

The ovum escapes into the oviduct by bursting the inner lining of
the ovary. It is surrounded by a layer of albuminous matter, and
is enclosed within a coriaceous chorion and an irregular deposited
nidamental tunic, by which the ovum, after exclusion, becomes at-
tached to the ciliated plates beneath the tail of the mother.

The first appearance of the embryo is as a whitish cloud of inde-
terminate form, spreading over the vitellus, and assuming, as it
extends, a reticulated appearance. A discoid portion of the layer
is defined from the rest, and increases in thickness at its middle part :
its longest diameter is about half the radius of the egg. A depression
appears in the centre of this, which passes more and more deeply into
the vitellus, and the embryonic spot expands at its margins. The
patch next grows heart-shaped, and the an-
tennae, the labrum, mandibles, and abdomen
become simultaneously recognisable. The
antennae {fig. 92, b and c), at first short and
simple processes, increase in length, and their
extremities become notched ; the mandibles
(d) also lengthen and enlarge, particularly in
their basal portion; tlie labrum (e) recedes
from between the anterior antenuce, and takes

Astacus fluviatilis.

188

LECTURE XV.

its station between the posterior : the eyes (a) now first make their
appearance. A cavity is formed behind the labrum, which communi-
cates with the commencement of the oesophagus ; the tail or abdo-
men (/) elongates^ and the depression in its surface is converted into
the anus ; the rest of the alimentary canal is a simple wide sac, which,
by the extension of the mucous layer of the germinal membrane, now
includes the vitelline mass.

The three anterior pairs of maxillag begin to show themselves
at a little distance behind the mandibles, and afterwards the fourth
and fifth pairs ; the last {Jiff- 93. ff 5.) increasing in size more rapidly
than the rest. Thus, including the eyes (a) and the two antennae (b, c),
nine pairs of appendages may now be recognised, of which the two last
belong to the thorax : the five posterior pairs of thoracic members,
which are not, like the first two, developed into jaws, are produced in
regular succession from before backwards from that portion of
the body which is turned upwards, or the epimeral elements of the
rudimental segments. Each of the legs at its first appearance is
exactly similar to the hindermost maxillae ; these, therefore, are
retained in the service of manducation by an arrest of develop-
ment. The ambulatory legs increase inversely with respect to the
maxillae, the anterior {Jig. 93, h 1.) soon acquiring four times the

length of the posterior (^ 5). The ru-
diments of the future branchiae next
appear as small processes from the base
of each leg. The seven segments of
the third division of the body (z) may
now be distinguished by six transverse
furrowSj and by the rudiments of foli-
aceous appendages.

The heart (5) appears at first in the
shape of a small compressed vesicle,
situated near the junction of the an-
terior and posterior segments of the
body': blood-vessels seem to be prolonged from it, and its pulsation
speedily becomes distinguishable.

The nervous system consists at first of eleven pairs of minute
white spots, from the anterior of which a short and broad process
passes forwards on either side of the oesophagus. The above described
stages of development are in progress from the beginning of April to
the middle of May.

The whole of the organs continue to approach more nearly to
their mature form. The brain, liver {ii), and salivary glands (^v), next
make their appearance. The outer integument of the body is de-
veloped from the ventral to the dorsal aspect, and the yolk-laden

Astacus fluviatilis.

CRUSTACEA. 189

intestine is finally, with the heart, walled in by the confluence of
the lateral lobes of the integument along the middle line of the back.

The integument is very soft when the animal quits the shell :
it subsists, at first, on the remaining portion of the yolk, during
which time its coat becomes sufficiently hardened to admit of its
moving about in quest of food with more safety. The different ap-
pendages increase in length, and more especially the branchiae, the
growth of which is now remarkably rapid. The changes of the in-
terior parts of the animal, with the exception of the development of the
sexual organs, consist in a gradual adaptation of parts already formed
to their j^roper functions.

The relative positions of embryo and vitellus are the same in the
craw-fish as in the Daphne pulex and Branchipus stagnalis. The
maxillae present at an early period a considerable resemblance to
those of the Apus : the legs at the period w^hen they are devoid of
branchial ajDpendages typify the persistent condition of the Branch-
iopoda : after the branchiae are developed, but before they are
enclosed in the branchial chamber, the characteristic persistent con-
dition of the respiratory system of the Edriophthalma and Stoma
poda is sketched out. M. M. Audouin and Milne Edwards have
shown that the successive changes of development of the nervous
system of the craw-fish correspond in like manner with distinct types
of formation observed by them in its permanent condition in lower
species of the class ; thus the double series of ganglions, which first
indicate the subcesophageal central part of the nervous system in the
embryo craw-fish, is analogous to the permanent state of the nervous
system in the mature Talitrus. At a more advanced period the two
series of ganglions in the foetal craw-fish approach the median line and
become united together as in the abdominal ganglionic chain in the
adult Cymothoa. We have seen that in the brachyurous Crustacea
a further concentration takes place by the longitudinal blending
together of the whole series of the suboeosophageal ganglia, which
clearly indicates that the brachyurous Crustacea are more highly
developed than the macrourous species ; contrary, however, to the
opinion of Dr. Rathke.

It is certain that the moult of the young craw-fish is not at any
period accompanied by a marked change in the form of the body, or
in the structure and functions of the locomotive members ; this Crus-
tacean, in short, undergoes no metamorphosis.

A series of less complete observations on the ova of a species of
land crab {Gecarcinus)^ more recently published by Mr. Westwood,
lead to the same inference in respect of that species. This ac-
complished entomologist coincides with Dr. Rathke in the general

190

LECTURE XV

conclusion that the Crustacea undergo no metamorphosis, and that
the contrary evidence adduced by Slabber and Mr. Thompson must
depend on some erroneous observation.

The opposite conclusions of both parties from the phenomena
afforded them by the solitary species examined, may be compared
with analogous generalisations which might have been drawn, in re-
ference to the class of Insects, by the observer of the development of a
cock-roach on the one hand, and by the observer of the metamorphoses
of a butterfly on the other. As reasonably might the one, after de-
tailing the progressive development of the orthopterous insect, broach
the inference that insects underwent no other metamorphosis than the
gradual acquisition of wings ; and, with equal reason, might the other
observer of the wonderful changes of the lepidopterous insect aflfirm
them to be characteristic of all insects. It needs only that each
theorist should question the reality of the other's observation to make
the parallel complete. The failure of both to arrive by so short and
easy a route at the entire truth, inculcates the necessity of acquiring
a sufficient foundation, by careful and extensive induction of facts,
before proceeding to erect the superstructure of general theory.

With regard to the metamorphosis of the common crab, valuable
testimony in confirmation of Mr. Thompson's discovery has been
contributed by Capt. Du Cane R. N.* This gentleman obtained crabs
with ova under their tails in the month of December, from which the
larvae were produced in the months of March and April : the form of
the larva at this period is shown 2iXfig. 94. Soon after exclusion this
larva casts off its envelope and assumes the
appearance represented in fig. 95., which
closely corre-
sponds with that
zoaeiform Crus-
tacean, whose
further changes
were witnessed
by Mr. Thomp-
son, and which
he had assured
himself was an
early or larval
state of a common crab. The last form which immediately precedes
the assumption of the mature characters corresponds, according to
Dr. Thompson, with that of the genus Megalopa.

The additional evidence afforded by Capt. Du Cane in proof of the

Larva of Crab.

Larva of Crab.

Annals of Natural History, 1 839, p. 438.

CRUSTACEA. 191

actual metamorphosis of the Crustacean in question, is most ac-
ceptable. He affirms a corresponding metamorphosis to occur in
the ditchprawn {Palemon variabilis) and common shrimp ( Crangon
vulgaris). Dr. Thompson has witnessed similar metamorphoses in
the genera Palinurus, Squilla, Pagurus, Porcellana^ Galatea, and the
marine species of Astacus, as well as in Palemon and Crangon.

Finally, the metamorphosis of another species of shrimp (Cari-
dina Desmarestii) have been described with all the requisite care
and detail by M. Joly, in the Annales des Sciences Naturelles for
January 1843. The development of the ovum up to the period of
exclusion and attachment to the maternal ciliated plates, closely cor-
responds with that described by Rathke in the Astacus fluviatilis.
The first stages in the formation of the rudimental extremities, the
first steps in the definition of the alimentary canal and circulating
system, were likewise the same ; the heart was observed to beat thirty-
five times in a minute in the embryo Caridina.

But the formation of the abdomen is anterior to that of the antennae,
the labrum, and the maxillas ; and the ambulatory thoracic legs precede
the masticatory pairs in their formation. The young Caridina, more-
over, is born with only three pairs of jaws, and the representatives of
the ambulatory feet are bifid, like those of the Mysis, and are at first
likewise only in three pairs. The abdominal segments are without
any vestige of lamelliform limbs.

The bifid feet of the larva are metamorphosed into auxiliary jaws,
and the later bifid thoracic limbs are metamorphosed into the ordi-
nary ambulatory legs. With respect to the branchiae they are not at
all developed when the young Caridina quits the ovum. The first
moult takes place three days after exclusion from the ^^^^ ; the sub-
sequent ecdyses are numerous, and take place at long intervals. It is
unquestionable that the Caridina, unlike the Craw-fish, is excluded
neither under the form, nor with all the parts which it possesses in its
mature shape. It wants, for example, the branchiae, a certain num-
ber of maxillae, the ambulatory thoracic, and the lamelliform ab-
dominal feet ; it possesses neither the squamous tail nor the complex
stomach of the mature creature.

The cumulative evidence of the metamorphoses of Crustacea can
no longer be rejected : but their modifications in different genera, and
the number of the exceptions to the law, like that presented by the
Astacus fluviatilis ■, are yet to be determined. Here, therefore, is an
ample field open to the researches of the original observer, a field
which must be diligently and extensively cultivated before it can
yield the fruits of true generalisations as to the extent and nature
and varieties of the metamorphoses in the class of articulate animals
which support their bodies on jointed limbs and breathe by gills.

192 LECTURE XVI.

LECTUEE XYI.

IIs^SECTA.

Although spontaneous locomotion is the peculiar attribute of the
Animal Kingdom, we have seen that the lowest members, the Zoophy-
tes as they were termed, were, for the most part, fixed and motionless,
like plants : we have seen that the first manifestations of locomotion
were of the feeblest and simplest character, a rowing of the body
through an element of equal density with itself, or a trailing of the
body along the ground, which supported it at every point. As we
advanced to the survey of the Articulate series of animals, we saw
the integument progressively hardened, divided into segments which
were united by flexible joints ; at length supported upon moveable
jointed limbs, consisting of hollow columns of integument hardened
into a dense exterior crust, capable of serving the office of levers
and fulcra, whereby the animal could raise its belly from the dust,
and swiftly traverse the surface of the ground.

We now come to a class oi Articulata, in which the highest problem
of animal mechanics is solved, and the entire body and its appendages
can be lifted from the ground and be propelled through the air. The
species which enjoy this swiftest mode of traversing space, breathe
the air directly : but their organs of respiration are peculiarly modi-
fied in relation to their powers of locomotion ; they consist of innu-
merable tracheae commencing from lateral pores called stigmata, or
by anal tubes, which are ramified through and over every tissue and
organ of the body. The nervous system is homogangliate ; the
organs of sense include two jointed antennae and two compound eyes ;
the skeleton is principally external, and cut deeply into segments,
whence the name of the class Insectn.

Not every Insect, however, has the power of flight, nor any Insect
save in its last and most perfect state ; many undergo most remark-
able transformations before they acquire their wings, and although
some Insects, which ultimately are so endowed, undergo a less
amount of change, yet the metamorphoses are always least remark-
able in the apterous species.

Of these lowest members of the class of Insects, many have more
than three pairs of legs, have sometimes indeed eighty pairs and
upwards in their mature state : metamorphic development exhausts
itself, as in the Anellides, in the successive acquisition of new segments

INSECTA.

193

and legs in addition to those which previously or originally existed ;
these Insects are therefore termed Myriapoda.

True or hexapod Insects have thirteen rings, one for the head, three
for the thorax, and nine for the abdomen. Certain flying Insects
in their early or larval state present several pairs of rudimental feet,
in addition to those attached to the first three segments, succeeding
the head, but no true Insect in its mature state has more than the
three pairs of articulated limbs just indicated.

Every Insect has a distinct head {Jig- 96, a), provided with one

pair of antennae (c), and its
trunk is divided into two
regions called thorax and
abdomen (a b).

The thorax is interposed
between the head and the
abdomen, and so far is ana-
logous to that part in hu-
man anatomy ; but it has
neither the same relation to
the contained viscera nor
to the locomotive extre-
mities which characterise
the thorax in the vertebrate
animals. To the Insect's
thorax are attached all the
locomotive members ; both
the first pair, which may
be compared w ith the pec-
toral extremities of the ver-
tebrate animal, and the last
pair, which may corre-
spond with the pelvic members, as well as the middle pair, to which
there is no analogue in the vertebrate series. This centre of the
locomotive powers is divided into three segments, which correspond
with the three pairs of legs : the first segment is termed the " pro-
thorax " (c?), the second the " meso-thorax " (/), and the third,
the "^ meta-thorax " (J,). Each of these segments has a dorsal and a
sternal piece : the dorsal half rings are called respectively " prono-
tum," " mesonotum," and " metanotum ; " the ventral or sternal arcs
bear the corresponding terms, " presternum," " mesosternum," and
" meta-sternum." From the inferior arches of the segments, the
legs (e, h, k) are developed, or with them they are principally arti-
culated, like the legs of the Crustacea and the ventral oars or seti-

o

Locusta.

194 LECTURE XVI.

gerous prolegs of the Anellides. In the flying insects there are
developed from the dorsal arches of the middle and third segments,
locomotive appendages which constitute the wings {g-,j)'

It must not be supposed that the parts of the thorax which have
just been described are naturally or uniformly separate, and moveably
connected with one another ; they are more commonly confluent, but
in different degrees in difl'erent families ; so as more or less to obscure
the primitive traces of their original distinctness, which can only be
demonstrated, as has been done by Macleay, Audouin, Burmeister,
and others, by an extended comparison of the thorax in the whole
class of Insects, or by tracing its development and modifications during
the various stages of the metamorphoses When the composition of
the thorax of an insect is thus studied, it is found to be made up of
not less than fifty-two pieces, which have for the most part received,
and necessarily, distinct names in Entomology, and many of them,
very unnecessarily, more names than one.

The abdomen is usually formed of a greater number of segments,
always nine in the larva, which retain a greater degree of mobility
upon each other ; but it supports no locomotive appendages in the
hexapod insects.

The tissue of the external skeleton is of a dense, resisting, but
light material ; it looks and feels like horn, but it has for its base a
peculiar substance called " chitine," which is insoluble in caustic,
potash, and retains its form like charcoal when submitted to a red
heat. The articulated appendages consist, like the segments of the
trunk, of hollow cases or tubes of the same firm and slightly flexible
substance; which tubes contain the muscles, nerves, and other soft
parts in their interior. The integument is softer and more yielding
in larvae, flies, and most parasitic insects. It consists of three layers,
epidermal, pigmental, and dermal, the derm and epiderm more
closely resemble each other in physical properties than in other
animals : they are separated and cemented together by sometimes
two distinct coloured layers of rete mucosum. The hairs, spines
and scales are processes of the epiderm, which often include a co-
loured substance.

I may now proceed to a more particular description of the jointed
and aliform appendages of the skeleton. The first pair inserted
into the front or upper part of the head, are the antennae, which
present a vast variety of shapes and sizes in different insects, but
seem in all to have most intimate relation to the senses of touch
and hearing. Their precise function has not, however, yet been well
defined. The Entomologist avails himself of their various conforma-
tion to obtain characters for the distinction of families, of genera, or

INSECT A. 195

of species of insects ; and a considerable section of the glossology of
this extensive department of Natural History is devoted to the
technical terms required to express the antennal characters. To the
head likewise belong more or less complicated oral instruments,
called " trophi," or "■ instrumenta cibaria," modified in some insect?
to serve for suction, in others, for mastication : they properly fall
under the demonstration of the digestive system.

The jointed legs attached, as before stated, to the three thoracic
segments, consist each of a hip, a thigh (A), a leg (/), and a foot (w),
commonly called the tarsus ; but which are not to be taken as
rigorously answerable to the parts so termed in Human Anatomy.
The hip, for example, consists of two joints, usually the shortest of
the whole leg: the foot or tarsus includes from two to five joints, and
is terminated by a pair of diverging hooks or claws. The peculiar
powers of moving upon land or in water depend upon the modi-
fications of the forms or proportions of these extremities. In water
insects the tarsi are usually flattened, fringed with hair, and stretched
out in the same plane with the trunk, like oars. In leaping insects
the hinder limbs present as disproportionate a development as the
legs of the kangaroo. In burrowing insects, the anterior limbs are dis-
tinguished by short, broad, and massive proportions, with a strong and
flattened hand, like that of the mole, as in this best of insect burro wers *,
which has been called the mole-cricket. Most insects are able to
crawl up vertical walls, and some along glass and the ceilings of
rooms, against gravity : the house-fly achieves this by virtue of the
development of little suckers upon the under surface of certain ex-
panded joints of the tarsus.

The wings of insects are essentially flattened vesicles, sustained by
slender but firm hollow tubes called " nervures," along which branches
of the tracheae, and channels of the circulation, are continued. The
wings never exceed two pairs, which are developed from the meso-
notum and metanotum. Sometimes one or other of these pairs is
wanting. The wings present many varieties in their shape, their
consistence, and their teguments. When they subserve flight, they
are thin and transparent ; or if opake, are rendered so by an im-
bricated clothing of most delicate scales, which, when detached,
resemble the pollen of flowers. In certain insects, especially those
that burrow, the first pair of wings become thick, hard, and opake,
forming a kind of shield to the back ; they are called " elytra," and
cover the posterior pair of membranous wings when these are not
expanded for flight. Sometimes the anterior wings are membranous

* Prep. No. 463, A.

o 2

196 LECTURE XVI.

at their extremities, hard and opake at their base, when they are
called ^' hemelytra." When the hinder pair of wings is wanting, it is
replaced by a pair of rudimental appendages called balancers : other
modifications of, or appendages to, the wings have been called " alulae"
and " patagia."

The muscular system is, as may be supposed, developed in relation
to the several kinds and powers of locomotion indicated by the modi-
fications of the extremities. As a necessary corollary of the cylin-
drical form and external position of the principal parts of the skeleton,
the joints are for the most part ginglymoid, and restricted to move-
ments in one plane. The muscles of the legs are consequently
simply flexors and extensors. The coxae have a round head inserted
into cup, and the movements of the hip-joint are rotatory ; the head
is usually connected with the thorax by a similar joint, which, from
the greater freedom of the movements, may be termed arthrodial.
In insects of flight, the cavity of the thorax is almost entirely
occupied by the muscles of the wings. The muscular fibre is trans-
versely striated, and is also characterised by a second series of trans-
verse indentations at regular but wider intervals.

The Orders of Insects are founded upon the modifications of the
wings ; those in which the first pair serve as sheaths, and the second
alone are used for flight, and are folded transversely when at rest,
constitute the order Coleoptera : they undergo complete metamor-
phosis, and are subdivided according to the number of joints of the
tarsi. Beetles and most burrowing Insects belong to this order.

Those insects in which the anterior pair of wings are converted into
elytra, of less density than in the Coleoptera, and in which the posterior
wings are folded longitudinally when at rest, constitute the order
Orthoptera : they are said to undergo a semi-metamorphosis, the chief
change being the acquisition of wings. This order includes the most
voracious and destructive Insects, as the Locust, Cockroach, &c.

Those Insects which have both pair of wings membranous, trans-
parent, strengthened by numerous nervures, and finely reticulated,
form the order Neuropiera, which includes the highest organised insects,
as the predatory dragon-flies.

The Insects which have four membranous wings simply veined, and
crossing each other horizontally when at rest, form the order Hyme-
noptera : they undergo a complete metamorphosis, and include the
most useful of insects, as the bee.

The Insects with four wings, more or less clothed with minute
scales, are called Lepidoptera : they undergo complete metamorphosis,
and include the most beautiful species of the class, as the butterflies :
in one family of this order the wings are divided lengthwise into a

INSECT A. 197

number of featliered pieces, which radiate from tlie body like the
stems of a fan. i^fig' 97.)

The Insects which have the anterior pair of wings in the condition
of the heraelytra, form the order Hem iptera; butcertain genera have the

dense part of the anterior wings
reduced to so small a strip, that
they are scarcely distinguishablcj
except by size, from the pos-
terior pair, and these insects
constitute a section of the order
termed Homoptera.

A few remarkable genera of
insects have the anterior pair of
wings reduced to small or rudimental elytra, and the posterior pair
unusually large, and folded longitudinally, like a fan when at rest.
The anterior wings being reduced to minute appendages twisted
spirally, the Order has been hence termed Strepsiptera, The species,
in their larval state, are parasitic on the bee tribe.

The order Diptera is characterised by the development of the an-
terior pair of wings into organs of flight, and the retention of the
hinder pair in the condition of minute clavate appendages, usually
called the "balancers." The prothorax and metathorax are rudi-
mental w^hilst the mesothorax is disproportionately large to form the
required space for the powerful muscles, which execute, through the
two anterior wings, the function of flight.

In almost every Order of Insects there are species, or there are
individuals, as the females of particular species, which are apterous ;
but since the time of Aristotle, who divided insects primarily into the
" winged," Ptilota, and the " wingless," Aptera, most of the hexapod
insects devoid of wings have been artificially grouped together. Cu-
vier and Latreille divide the Apterous Insects into three tribes, the
Suctoria (fleas), the Parasita (lice, including the Pediculus capitis
and Pthirus inguinalis of the human species), and the Thysanoura,
including the Lepisma and Podura or skip-tails.

The grand and characteristic endowment of an insect is its wings ;
every part of the organisation is modified in subserviency to the full
fruition of these instruments of motion. In no other part of the
Animal Kingdom is the organisation for flight so perfect, so apt to
that end, as in the class of insects. The swallow cannot match the
dragon-fly in flight ; this insect has been seen to outstrip and elude
its swift pursuer of the feathered class ; nay, it can do more in the
air than any bird, it can fly backwards and sidelong, to right or left,
as well as forwards, and alter its course on the instant without turn-

o 3

198 LECTURE XVI.

ing. Now what are these " limber fans," that give the little articulate
animals such command over aerial space ? I do not mean their
structure or composition ; the anatomical question has been already
answered. I do not ask for their analogy ; that is rightly expressed
by their common name ; they have the same relation to the insect as
instruments of motion, which the feathered wing bears to the bird.
But what is their essential nature, or with what are the wings of the
insect homologous ? Are they modified anterior limbs, like the wings
of bats and birds and flying-fishes ? Not so, for they co-exist with and
are superadded to the jointed anterior pair of legs. Are they such
expansions as form the parachute of the little dragon {Draco volans)?
These do, indeed, co-exist w ith arms and legs, but they consist of a
fold of integument stretched out upon elongated and straightened
ribs, which are appendages of a vertebral column. But an insect has
no vertebral column, no true internal skeleton. The strong and nu-
merous nervures which sustain the thin alar membranes of the Libel-
lula are articulated processes of the external chitinous tegument.

A circulation can be traced through these membranes, at least in
their early and softer state ; air-vessels are abundantly spread over
the supporting frame-work: the wings of the Lepidoptera appear
after the third moult, as tegumentary flattened vesicles, soft, and per-
meated by tracheae, and when fully expanded in the imago, they must
still take their share in the business of respiration. Nay, it has been
found that the rudimental wings of the pupse of certain water insects
are the gills of such ; they perform the same function as the very
similar membranous and vascular tegumentary expansions in certain
Anellides (see ^^. 68. p. 130.) ; which expansions are developed, as
in the larvae of the Ephemera, from the tergal arch of the segment,
and co-exist with rudimental legs from the ventral arch of the same
segment.

Well, therefore, has the deep-thinking Oken * called the wings of
insects " aerial gills ; " they are, in fact, the homologues of the tergal
branchiae of the vermiform Articulata, raised to a higher function in
corellation with a generally transmuted state of the rest of the
organisation, which is advanced to the utmost perfection of which
the Articulate type of structure is susceptible. And have we not
already seen the membranous aliform branchiae of the beetle pro-
tected, like the gills of the lobster, by an elytral carapace developed
from a more advanced segment ? Have we not likewise found the
metamorphosed branchial wings of the Pterophora subdivided length-
wise like the tufted tergal gills of the Nereis ?

* Natur. Philosophic, 2d Ed. p. 418.

INSECTA.

199

The air-breathing articulated animals with jointed legs offer a close
correspondence with those that respire by gills in the progressive steps
of complication of the nervous system and the order in which those
steps succeed each other. The lowest insects, like the lowest Crus-
taceans, resemble the worms, in the great length and slenderness of
their body, and in the uniform size, shape, and number of the con-
stituent segments. In the lulus, whose very short and numerous
rings support each two pairs of rudimental legs, the corresponding
ganglions of the abdominal chords are much less conspicuous than
in the earth-worms, and the whole central axis of the nervous
system, continued from the brain, is almost as devoid of partial
swellings as the spinal chord of the apodal vertebrate. It lies^ how-
ever, as in other Articulata, on the opposite side of the body to that
in which the brain is situated.

The cephalic ganglion (Jig.98. a) of the lulus is transversely elon-

lulus.

gated, and obscurely divided by a slight median indentation into two
side-lobes : its upper and latter extremities are prolonged outwards
into the short and thick optic nerves (c, c), which resolve themselves
half way towards the compound eye into a plexus of filaments for its
several divisions. Two separate antennal nerves, conjectured by Straus
to be motory and sensory (d, d), are sent off on each side below

o 4

200 • LECTURE XVI.

and in front of the optic nerves to the short seven-jointed antennae.
On each side also, but below the antennal nerves, arise the two nerves
{b) united together by an anastomosing branch which supply the palp-
less mandibles.

The thick oesophageal chords (^) are continued from the pos-
terior and inferior angles of the brain ; and, though apparently simple,
consist essentially of two chords, which become separate at the lower
part of the pharynx : the anterior chord girts the pharynx by a trans-
versely oval ring, formed by its confluence with its fellow ; the pos-
terior and normal columns converge, at an acute angle backwards,
blend together, and expand into the commencement of the abdominal
nervous trunk ; thus inclosing the oesophagus by a second and looser
collar. The closer anastomotic ring is analogous to that formed by
the transverse commissural band of the cesophageal chords in the
lobster and limulus ; and probably also to the anterior nervous ring
discovered by Lyonnet in the Cossus ligniperda. The stomato-gastric
nerves (/), which arise from the posterior part of the brain, imme-
diately form a third slender ring (e), about the oesophagus, from the
middle of the upper part of which the trunk of the stomato-gastric sys-
tem is continued a short way back upon the stomach, when it divides ;
the two divisions diverge at an angle of 45°, bend abruptly back-
wards, and run parallel with each other along the dorso-lateral parts
of the wide and straight alimentary canal.

Two large nerves (A) are sent forwards from the beginning of the
thick suboesophageal or ventral chord (i, i), to supply the confluent
maxillae, which form the under lip : the nerves of the two single pairs
of feet, belonging to the thoracic segments, next arise, and afterwards
the more numerous minute nerves to the little feet, which, by their
articulation to the segments in double pairs, indicate such segments to
be severally a confluence of two. The simplicity of the abdominal
chords corresponds with the close approximation and great numbers
of the organs from which they receive impressions and to which they
transmit stimuli. The analogy of this exceptional condition of the
abdominal chord or nervous axis in the lulus to the dorsal spinal
chord of the Vertebrata, is as instructive as is that of the equally
exceptional ganglionic condition of the spinal chord in the Tetrodon
amongst fishes to the normal abdominal knotted chords in the Arti-
culata, in tracing their mutual relations to each other,

The segments of the Polydesmus are relatively fewer and larger
than in the lulus, and their lateral margins are produced : each, how-
ever, with the exception of the first three, which answer to the thorax
in hexapod insects, supports two pairs of legs : but these are longer
than in the lulus. Accordingly we find the sub-abdominal nervous

INSECTA. 201

chords {fig. 99.), which show as little trace of their median separation
as in the luli, swelling into two slight enlargements (^, g) opposite each
of the abdominal segments : two nerves are sent off from either side of
each enlargement, and the anterior of these four pairs of nerves
is directed at an acute angle forwards and outwards to the stigmata :
the remaining pairs supply the muscles of the segment and the legs,
and are of equal size.

In the Centipede, a series of equal and equidistant
ganglia is developed upon the ventral surface of the two
abdominal chords. Only in the first and last of the ab-
dominal ganglions can any modification of size be de-
tected. The anterior, or sub-oesophageal ganglion, for
example, is larger than the rest, having to supply the
modified legs which perform the function of jaws and
under lip ; the chords, diverging as they escape on each
side of the oesophagus, enclose it by uniting with the
large bilobed ganglion, or brain above. The nerves
from this part supply the large antennae and the aggre-
gated ocelli. In the structure of the abdominal co-
lumns a tract less closely connected with the gangli-
onic nerves may be traced along their dorsal aspect.
This was first pointed out by Mr. Newport, who attri-
butes to it the motor function. A large, vascular
trunk, connected also with the dorsal aspect of the ner-
Poiydesmus. ^^"^ systcm, has been regarded as part of the nervous
system ; by some as a motor, by others as a respiratory
column : its true nature was detected by Mr. Lord.* With regard to
the ganglionic and non-ganglionic portions of the true nervous axis,
the same physiological reasonings will apply as have led to the
conclusions already given respecting their office in the crustaceous
animals.

Of the four nerves which come off* from the sides of the ganglionic
portions of the columns, the second, which is principally distributed
to the muscles of the corresponding pair of legs, arises in a great pro-
portion from the ganglion itself. The first and third nerves, which
are smaller than the second, supply the muscles and integuments of
the segment. The fourth pair of nerves passes to the breathing
pore and to the integument. This, therefore, must be regarded as the
respiratory nerve. The stomato-gastric nerve is a distinct system
connected with the anterior ring or brain.

Thus in the Myriapodous insects we find that although the prin-

* Med. Gazette,. March 3d, 1838.

202 LECTURE XVI.

ciple of irrelative repetition prevails in the nervous system as in the
skeleton and locomotive instruments, yet it does not prevent the re-
cognition of the leading physiological divisions of that system. We
have, for example, the supra-oesophageal or cephalic portion, which is
subservient to the functions of the special organs of the senses, and is
the centre whence voluntary impulse may be directed along the non-
ganglionic tracts of the nervous axis, and to which ordinary sensa-
tion may be transferred by similarly uninterrupted nervous filaments.
We have, secondly, a large sub-cesophageal mass, which, originating the
nerves analogous to the fifth pair, for the masticating organs and
other parts of the head, may be regarded as analogous to the medulla
oblongata. In the abdominal chords and ganglions we have the re-
quisite machinery for the automatic reception and reflexion of stimuli,
independently of sensation and the will ; and to these are superadded
internuntiate and uninterrupted chords, for bringing the body under
the dominion of the will, and for producing harmony and consent of
action throughout its extent. The special nerves to the respiratory
system, and the stomato-gastric nerves, complete this already compli-
cated nervous system.

In the hexapod insects the nervous system differs chiefly from that
in the Myriapods in having its primary divisions more definitely de-
veloped, and in manifesting degrees of concentration corresponding
with the increase of bulk and strength in particular parts of the trunk,
and in the locomotive organs appended thereto. Most insects, how-
ever, commence their career as worms ; the high form which they are
ultimately destined to attain in the articulate series is at first masked by
the guise of an Anellide or Entozoon. Some insects retain their larval
or vermiform state much longer than others ; and after passing a great
proportion of their lives under this form, fall into the state of the pupa,
or chrysalis, relapsing, as it were, a second time into the condition of
an ovum^ there and then undergoing that part of their development
which before was left incomplete, and finally, emerge in their perfect
state to enjoy for a brief period the highest faculties, animal and
organic, which they are destined to acquire ; fluttering in the air, it
may be, for a single day, procreating their kind, and perishing. Now
the development of the nervous system, like that of the muscular,
digestive, and other systems, being completed at distinct and some-
times remote periods, requires to be studied in the first and last of the
active states of the insect, and also in the intermediate period, when,
owing to the rapidity and extent of the changes which it undergoes,
the nervous system off"ers to the comparative anatomist and physiologist
phenomena of the highest interest.

The apodal Entbzoiform larvae, in which the segments of the body

INSECTA. 203

are obscurely defined, as those of most Diptera, Hymenoptera, and
of some Coleoptera with very rudiment.al feet, have a simple ven-
tral nervous chord, almost as devoid of ganglionic enlargements as
in the Nematoideaand lulidse: it is, however, usually relatively shorter,
failing to reach the posterior extremity of the body, and the fine nerves
pass off on each side and radiate from the extremity.

In the larva of Stratiomys chamceleon the ventral chord is divided
by a series of constrictions into eleven consecutive and contiguous
ganglia.

The larvae, which present, like the Centipede, larger and more
definite segments, most of which are provided with legs or prolegs,
have a ganglionic centre for each segment, and intermediate chords.

This anellidous and chilopodiform type of the nervous system has
been best described and figured by Lyonnet. The subject which this
inimitable dissector and artist selected for his patient investigations
was the caterpillar of the Cossus ligniperda. The nervous axis
consists of thirteen ganglions, arranged along the median line of the
body, and connected by two chords or columns. The first and largest
ganglion, situated in the head above the mouth, and of a bilobed form,
Lyonnet calls the brain ; the remaining twelve ganglions (as in Jig.
104, 1 to 12.) are situated below^ the alimentary canal ; the eleventh
and twelfth are so close together that their distinction might readily be
overlooked ; but it was pointed out by Lyonnet. The sub-abdominal
ganglions and inter-communicating chords were called by Lyonnet
the spinal marrow\ Some anatomists who have applied the analogy
of the ganglionic and non-ganglionic roots of the spinal nerves in the
higher Vertebrata to the explanation of the functions of the ganglionic
and non-ganglionic parts of the nervous axis in Insects, have thought
that they found in the works of Lyonnet corroboration of this in-
conclusive physiological view. Lyonnet, however, expressly denies that
the parts which he called brain and spinal marrow in the insect were
similar in anatomical structure to those in the higher animals.

" The spinal marrow of the caterpillar, if one may say that it pos-
sesses such," observes Lyonnet, " sensibly differs from that of man.
It is slender ; it bifurcates at intervals, and enlarges from distance
to distance to form its masses, which I have named ganglions."
The intervening chords Lyonnet terms " conduits de la Moelle
^piniere." He particularly points out the difference in relative posi-
tion, and in the means of protection assigned to the ganglionic
columns in insects, and to the spinal chord in the higher animals.
As to any views of distinct physiological properties in the ganglions
or the non-ganglionic nervous tracts, none such appear in the
works of Lyonnet ; nor, indeed, did they form part of the do-

204 LECTUKE XVI.

main of physiology at that period ; and it was a great advantage to
Zootomy that Lyonnet looked at his subject with the eye of truth,
and not through the prism of any pre-formed physiological notions.

The supra- oesophageal ganglion gives off ten nerves ; eight in pairs,
and two solitary or azygos nerves ; one of these latter is the anterior
oesophageal ring, which Mr. Newport has figured and described in
the Sphynx ligustri. Its extremities are connected with the cephalic
ganglion immediately anterior to the attachment of the principal
columns which form the posterior oesophageal ring. The second
solitary nerve is sent off from the middle of the posterior side of the
cerebral ganglion, and proceeds backwards to the oesophagus. The
cephalic nerves, sent off in pairs, supply the antennae, the ocelli, the
muscular and integumentary parts of the head, and communicate
with branches of the maxillary nerves. The most remarkable pair,
however, is that which arises anterior to the annular or oesophageal
nerve, and which constitutes the cephalic roots, or connections of the
stomato-gastric system. Each of these nerves passes forwards and
divides ; the external tract joins one of the maxillary nerves of the
suboesophageal ganglion. The internal one converges towards its
fellow, and terminates with it in the first of the median cephalic series
of ganglions, Avhich Lyonnet terms frontal ganglions. The longest
nerve in the whole body of the caterpillar is given off" from these
ganglions as it passes along the oesophagus to the stomach and in-
testines : it w^as called by Swammerdam the recurrent nerve. There
are two other small ganglions situate in the head of the caterpillar on
each side of the large bilobed or cephalic ganglion. The largest
nervous columns connected with the supra-oesophageal ganglion, are
those which enclose the oesophagus by uniting with the first of the
lower series of ganglions. From this ganglion nerves are distributed
to the mandibles, the maxillae, the lips, and their special organs of
sensation or palpi. Two distinct diverging columns connect the first
wdth the second ventral ganglion ; and this is similarly connected with
the third. The inter-communicating chords of the remaining gan-
glions appear single at their anterior part, and bifurcate as they are
connected with the next ganglion in succession. They are of a
greyish blue but transparent colour, and are very elastic. From
each side of the abdominal ganglions are given off two principal
branches ; the anterior to the muscles chiefly, the posterior chiefly to
the integuments^, but communicating with the muscular branch of the
succeeding ganglion. From the beginning of the separation of the
bifurcated inter-ganglionic columns, or conduits, Lyonnet says, "^ there
descends a nerve, the extremity of which is enlarged a little above the
succeeding ganglion, which sends off from the enlargement a trans-

INSECTA. 205

verse nerve to the right and to the left, to which I give the name of
spinal rein (bride epiniere). Of these transverse nerves there are
ten pairs ; they terminate chiefly in the stigmata and tracheae, but
send off small branches to the skin and to the dorsal vessel. These
are the respiratory ganglia and nerves, and have been erroneously
considered as the motor column and nerves.

The nervous system in perfect insects approaches to its larval con-
dition according as the segments of the body and their locomotive
appendages are less concentrated and developed ; thus, in the darkling
beetle {JMeloe) the abdominal nervous columns still manifest eight
distinct ganglions, of which the last, perhaps including three ganglions
of the larva, is now the largest, and radiates its branches to the gene-
rative organs. The first, or sub-cesophageal ganglion, sends forward
four median branches to the under parts of the mouth, and is connected
with the brain by the two lateral chords forming the post-oesophageal
collar. The usual nerves are given off from the brain, those to the
eyes having acquired an increase of bulk, corresponding with the
great change in the size and complexity of the organs of vision. The
stomato-gastric nerves arise close to the antennal branches, and form
a median frontal ganglion, and are connected with a pair of lateral
ganglions : from these the usual recurrent nerve is given off. In the
thorax w^e distinguish the second ventral ganglion, which, as it dis-
tributes branches to the first pair of legs, I have called the brachial
ganglion. The third ventral ganglion supplying, amongst other parts,
the elytra, may be termed the elytral ganglion. The fourth ventral
ganglion is distinct in the present species, and, supplying the nerves to
the second or true wings, may be termed the alar ganglion. The fifth,
sixth, and seventh, or first three ganglions in the abdomen, distribute
nerves to as many large and moveable segments of that division of the
trunk : the last ganglion is the largest, and its size is conformable
with the bulk of the generative apparatus, upon which, on the rectum,
and the modified terminal segments of the abdomen, its branches are
expended.

In insects having the organs of flight better developed, the elytral
and alar ganglia present a greater proportional size ; but different
degrees of concentration in the centres of the nervous system are
met with in these higher forms of insects. In the Blattae, for ex-
ample, there are as many as ten distinct ventral, or inferior ganglions.
The supra-cesophageal nervous centre or brain is a transversely
oblong bilobed mass, sending its upper and largest pair of nerves
to the eyes. Anterior and below the antennal nerves arise from small
mamillary processes of the brain, reminding us of olfactive lobes.
The stomato-gastric nerves are seen a little in advance of those

206 LECTURE XVI.

in the deflected part of the head. The oesophageal chords are short,
uniting in a maxillary ganglion, or first of the ventral series, M'hich is
situated in the head ; the inter-communicating chords, which pass from
this to the brachial ganglion, are long, straight, parallel, and juxta-
posed. The brachial ganglion sends off two large and two small pairs
of nerves, the anterior ones are distributed to the muscles of the arm,
which are lodged within the anterior portion of the thoracic shield ;
the second nerve is continued to the terminal segment of the anterior
extremities like the second nerve from the ganglions of the centipede.
The elytral ganglion, or the third of the ventral series, is larger than
the preceding one. Viewed from the dorsal aspect, it is seen to dis-
tribute three small nerves to the muscles of the wing-cover ; the pos-
terior branch, anastomosing with the nerve sent from the succeeding
ganglion to the wing, thus serves to combine these organs of flight in
action in the Orthopterous insects. In the Coleoptera, whose elytra do
not move in flight, this anastomosis of the nerves does not take place.
Four pairs of nerves come into view when the elytral ganglion is ex-
posed from below : the anterior of these runs forward at an acute angle
to the muscles of the first and second pairs of legs. The next two anas-
tomose with an alar branch. The third pair enters the second pair of
legs, and is distributed to their terminal segments. The posterior nerve
passes to the alar plexus. The substance of the bilobed elytral ganglion
seems to be superadded to the under or ventral part of the nervous
chord. The alar ganglion, formed by a confluence of the fourth and
fifth of the larval ganglions, is situated at the same distance from the
elytral as this is from the brachial ganglion. It is not quite so broad
as the elytral ganglion, the wings which it supplies being shorter than
their covers. The anterior nerve enters into communication with the
elytral branches, as does also the second nerve, with the addition of
branches to the muscles of the legs. The third nerve is distributed
to the third pair of legs ; the fourth to the muscles of the wing. The
remaining six ganglions of the ventral series are contained in the ab-
domen : they are smaller than the preceding, the distance between
them progressively increasing after the third. The last, formed by
the confluence of the eleventh and twelfth ventral ganglions of the
larva, is of a triangular form, and the largest of the series. It sends
off" a pair of conspicuous nerves to the cercse or anal antennae. The
two interganglionic columns are in contact lengthwise from the head
to the anal ganglion. In the Meloe they are smaller, and separated by a
marked interspace. The respiratory nerves may be seen on the dorsal
aspect above the second, third, and fourth ventral ganglion. If the
nervous system of the Blatta be compared with the stages of deve-
lopment of that system in an insect presenting a more concentrated

I

TNSECTA. 207

type in the perfect state, as in the species of butterfly described by
Heroldt, it will be found to correspond with the sixth stage figured by
this author in the pupa of the Papilio brassiccB.

In the predatory leaf insect {Mantis) the progress of coalescence
has reduced the number of abdominal ganglia to four, the three tho-
racic ganglions continuing distinct, so that the nervous system cor-
responds with the eighth stage figured by Heroldt in the Lepidop-
terous insect just mentioned. The supra-cesophageal mass consists of
two triangular lobes having their bases rounded and anterior, and
their apex prolonged into the oesophageal chords. Two small nerves
are sent off" from, the anterior part to the ocelli, where they swell into
a slight enlargement. Two short and thick optic nerves pass from
the sides of the brain to form the ganglions supplying the large com-
pound eyes.

The stomato-gastric nerves arise, one on each side^ near the optic
nerves. The oesophageal columns are short, and directly converge to
the inferior cerebral ganglion, which gives two large and several
small nerves to the jaws : it is situated in the head. Two long and
parallel columns extend to the first thoracic ganglion, which trans-
mits long and large nerves to the formidable prehensile anterior pair
of legs. The second thoracic or elytral ganglion is at a great dis-
tance from the first, and much nearer the third or alar ganglion.
Anastomosing branches connect the nerves which these ganglions
respectively distribute to the elytra and wings. The Mantis is
chiefiy remarkable for the great length of the ventral chords con-
necting the brachial with the elytral ganglia, and which renders
them favourable for minute analysis of their structure. Anterior and
posterior columns, or divisions analogous to those in the spinal mar-
row of higher animals, cannot be distinguished. The so-called sen-
sorial tract is confined to accumulations of nervous matter at the
origin of the nerves to the locomotive organs.

The results of the experiments in which the body of the living
Mantis has been so divided, that a segment with one of these
ganglionic enlargements and the locomotive organs it supplies has
been detached from the rest, illustrate the functions of the aggre-
gated centres of nervous matter in relation to their power of receiving
and transmitting impressions, so as to maintain the order of action o
such detached organs upon the application of a stimulus, for a con-
siderable period after the mutilation.

The jaws of the separated head of a Mantis bite forcibly the stick
which is held to them. The formidably armed prehensile legs in
like manner wound the finger that touches them, when the segment
of the body supporting them is separated from the head and the rest

208 LECTURE XVI.

of the trunk. And if decapitation or amputation of the prothorax be
neatly performed on the living insect, while in its natural and ordinary
position, perched by its middle and hinder pairs of legs upon a twig,
the rest of the trunk does not fall to the ground, but is maintained
for a certain period in that posture, which it even recovers by actions
of the wings, when the balance is slightly and purposely disturbed.

The supra-CEsophageal or cerebral mass in insects obtains its largest
development in the dragon-fly, which from the size and perfection of
its organs of vision, its great and enduring powers of flight and pre-
datory habits, may be regarded as the eagle of insects. From the
side of each of the superior lobes of the brain, the optic nerve is con-
tinued of equal breadth, so as to seem rather as a lobe of the brain.
It expands, and, like the stalk of a mushroom, forms the stem of a
very large reniform ganglion, the convexity of which is turned for-
wards and outwards, and the free concave projecting margin de-
veloped at the under part. Thousands of branches to the divisions of
the compound eye are given off from the convex surface of this
ganglion. The brain presents a single median inferior lobe ; the
oesophageal chords sent downwards to the maxillary ganglion are
short and thick. This ganglion is succeeded by three large equi-
distant thoracic ganglia, of which the last two, corresponding with
the elytral and alar ganglions of the preceding insect, are, as might be
expected, from the development of the muscles of the wings (both of
which are alike organised for flight), considerably the largest. Of the
ganglia of the abdomen, the terminal one resulting from the con-
fluence of two, and which supplies the organs of generation, is remark-
able for its large size.

In the white butterfly (Papilio hrassiccB) the brain is a thick trans-
verse rounded mass, indented by a longitudinal furrow along the
median line. From its sides proceed the large optic nerve, now greatly
surpassing the other cerebral nerves in size. The oesophageal collar
is triangular, leaving a very small interval for the passage of the
alimentary gullet. The maxillary ganglion is relatively much smaller
than in the dragon-fly, the blatta, and other mandibulate insects.
The first two thoracic ganglions are blended into one, and the third
thoracic and first abdominal ganglions have coalesced to form a
similar mass in the thorax, connected with the preceding by short
chords, separated by an interval to allow the passage between them
of certain processes of the thorax giving attachment to the muscles of
the legs. The ganglions of the thorax have been observed in some
species (as the Bomhyx Neustria) to present a reddish tint. They are
succeeded in the Lepidoptera by four other ganglions in the abdomen,
of which the last, as usual, is the largest.

INSECTA. 209

The nervous system of the chaffer {Melolontha) has been dissected
and delineated by Strauss with a minuteness and accuracy second
only to those of Lyonnet. In these beautiful plates * are shown the
bilobed brain with its auxiliary ganglia for the eyes and antennae ;
the storaato-gastric nerves and their small lateral cephalic ganglia
are also clearly exhibited. The sub-oesophageal or maxillary ganglion
is of an oblong form ; the brachial ganglion is triangular ; the elytral
ganglion is of a circular, and the alar ganglion of a pyriform, figure ;
these two latter being concentrated into almost a single mass, and
radiating the nerves to the abdomen, like the termination of the spinal
marrow called cauda equina. The two median nerves of this series
chiefly supply the organs of generation.

The three thoracic ganglia are blended together into one mass in
the Diptera ; and only two ganglions are developed on the abdominal
portion of the ventral chords.

The greatest degree »f concentration of the nervous system is pre-
sented in the insects of the Hemipterous order. In the Nepa or
water-scorpion, for example, only three ganglions are present in its
nervous system. The first, or brain, consists of two pyriform lobes in
contact by their base. The maxillary ganglion is square-shaped, re-
ceiving the oesophageal chords at its anterior angles, and sending back
their continuations from its posterior angles ; these continue parallel
with each other to the thorax, there expanding into a large rounded
ganglion, much more voluminous than the brain, and from which
radiate the nerves supplying all the rest of the body.

In certain Coleoptera, Hymenoptera, and Diptera, the principal
changes which the nervous system undergoes in the progress to the
imago state, are the acquisition of ganglions not present in the larva.

The progressive changes which the nervous system of the Lepi-
dopterous insect undergoes in its metamorphoses from the larval into
the perfect state, have been beautifully and accurately illustrated by
Heroldt in the cabbage butterfly, and by Mr. Newport in a species
of sphynx : but Lyonnet had anticipated both these observers, in re-
cognising as well the principle as the details of these changes, which
he briefly describes at the termination of the monograph already
quoted.

The twelve ventral ganglions of the larva (^fig. 103.) are sub-equal
and, except the two last, at regular distances ; in the pupa the inter-
ganglionic columns are shorter, but the body, becoming still more
abbreviated and concentrated, throws those columns into curved lines.
The eleventh and twelfth ganglions coalesce ; the sixth and seventh

* Here the work, entitled, " Considerations generales sur I'Anatomie Comparee
des Animaux Articules," &c., 4to. 1828. was shown.

P

210 LECTURE XVI.

disappear ; the fifth blends with the fourth^ and the third with the
second ; thus leaving four ganglions in the abdomen and two in
the thorax (^^. 104-.). Corresponding changes take place in the
cerebral portion of the nervous sj^stem. The maxillary ganglion de-
creases with the diminution and change in the maxillary apparatus.
The oesophageal collar contracts, as does the canal which it surrounds.
The brain enlarges, having to supply organs of sense, especially those
of sight, which are perfected to correspond with the acquisition of
new and improved locomotive forces. Analogous changes we may
naturally conclude to take place in other orders of insects ; and we
find, indeed, in some of these that the nervous system continues sta-
tionary at stages of development which are progressive and transitory
in the Lepidoptera, and that further concentration is discovered to
have taken place in the Melolontha, Cicada, Nepa, &c., than that
which constitutes the highest stage observed by Heroldt and Mr. New-
port in the Lepidoptera. The marvel is, that these changes, due in
part apparently to mere mechanical influences, should be so regular,
so orderly, so admirably adapted in their final results to the general
condition and exigencies of the perfect insect: one might have sup-
posed that the particles of the soft and semi-fluid nervous matter,
squeezed by the pressure of the surrounding parts, when the body
seems to be, as it were, contracted by an universal spasm, would be
irregularly dislocated or aggregated into one or more masses ; but,
on the contrary, we perceive the nervous particles moving forwards
and re-arranging themselves in orderly groups, definite in their forms,
in their proportions, and in their relative positions ; these being ap-
parently regulated by a law of prospective arrangement and arranged
precisely in those situations where the greatest supply of nervous
energy is required to radiate from them in the active and perfect
insect.

An idea of the situation and degree in which the sense of touch is
exercised in insects may be formed by observing the modifications of
the diflferent parts of the integument, the papillas, or folds upon its
surface, the hairs, plumes, or soft jointed organs developed from par-
ticular parts of the body. The soft balls on the feet of grasshoppers,
the pulvilli and suckers on those of flies, the soft, setaceous, or
plumed antennae, and, above all, the palpi, often provided with a ter-
minal vesicle, present the requisite physiological conditions of the
organ of touch. Although another sense, and most probably that of
hearing, may reside in the antennae, yet no one can witness the use of
these organs by bees and ants, the exploratory actions of those of the
ichneumon and of many other insects, without recognising in them
instruments of the tactile faculty.

INSECTA. 211

All Mandibulate insects have a process from the labium, within
the mouth, so analogous to a tongue as to have received that name.
It is particularly well developed in the dragon-fly and grasshopper, in
which its soft, finely ridged, upper surface receives a rich supply of
nerves. It is not present in the suctorial insects, which, as Burmeister
well observes, always subsist upon one and the same food, generally
inhabit what they feed on, and consequently less require the sense of
taste.

Although a few physiologists have suspected that some part or
appendage of the head, and others that the membranous lining of
the spiracles were the organs of smell, the precise seat of that sense,
which unquestionably exists in insects, has not yet been experi-
mentally determined. The application by the common house-fly of the
sheath of its proboscis to particles of solid or liquid food before it
imbibes them, is an action closely analogous to the scenting of food
by the nose in higher animals : and as it is by the odorous qualities
much more than by the form of the surface, that we judge of the
fitness of substances for food, it is more reasonable to conclude that
in this well-known action of our commonest insect, it is scenting,
not feeling, the drop of milk or grain of sugar. But no one ever
saw an insect present its spiracles to a nutritive substance before
feeding.

The signs of attention and hearing are plainer in insects than
those of smelling ; yet the precise organ has not yet been more defi-
nitely recognised, unless the structure, peculiar, however, to moths
described by Treviranus, be the true seat of the auditory sense ; it
consists of a simple drum situated in front of the base of each an-
tenna. It is strange, however, that the organ under so well marked a
form should not exist in crickets, tree-hoppers ( Cicadce), and other
insects which attract their females by peculiar notes. Only the soft
capsular membrane of the joint of the antenna, which in some move-
ments may be rendered tense, has been alluded to by Burmeister as
a structural indication of the organ of hearing in the peculiar ap-
pendages in which he supposes, with most other entomologists, that
the sense resides. The acoustic nerve quits the antennal nerve, in the
Crustacea, as if it were a branch of that nerve. Two, at least, and
often more numerous nervous filaments from a slight ganglionic en-
largement, penetrate the antennae in insects; and these may sub-
serve the distinct offices of the appreciation of the vibrations of sound,
of the characters of surface, and of the regulation of the movements
of the antennae.

Of all the organs of the special senses not only is that of sight

p 2

212 LECTURE XVI.

manifest without ambiguity, but it is more complicated and relatively
larger in insects than in any other class of animals.

What would be thought of a quadruped whose head, with the ex-
ception of the mouth and the place of juncture with the neck, was
covered by two enormous convex masses of eyes, numbering upwards
of 12,000 in each mass? Yet such is the condition of the organs of
vision in the dragon-fly, which, besides the two great compound eyes,
supports, in the narrow interspace on the vertex of the head, three
simple eyes, called ocelli and stemmata.

In all insects the eyes are sessile, or, if supported, as in a few rare
instances, on prolongations of the head, such peduncles are not
moveable like those which support the compound eyes of the higher
Crustacea.

The Centipede has many simple eyes, arranged in a cluster on
each side of the head, and requiring only a little closer approximation
to form a compound eye. The required approximation takes place in
the lulus, but the optic nerve, instead of swelling into a ganglionic
mass, separates into a pencil of nerves at the base of the cluster, one
for each ocellus. The transition to the large compound eye of the
hexapod is made by the lulus and Scutigera ; but the interval is very
wide between the Myriapods and Anellides in regard to both the
number and structure of the organs of vision.

The lateral compound eyes of winged insects are generally cir-
cular, sometimes oval, or reniform ; they occupy the sides of the head,
and sometimes encroach upon the upper part so as to meet there.
In some Capricorn beetles, as Tetraopes, the antennae project from
the middle of the ovate eyes and divide them into an upper and lower
half: the compound eyes of certain beetles of the genera Ateuchus
and Geotrupes are almost or quite divided into two on each side by
the encroachment of the canthus ; some Ephemerce and the Gyrinidce
have two pairs of compound eyes : in the latter they are situated one
on the upper, the other on the lower surface of the head, and must
serve the aquatic whirligigs to discern at the same time objects be-
neath them in the water, and above them in the air.

The integument of the head, which passes uninterruptedly over the
compound eye, then becomes transparent, and is subdivided into a
number of hexagonal corneules, varying in number from 50 in the
ant, to 4000 in the house-fly, to above 17,000 in the butterfly, and to
more than 25,000 in the Mordella beetle. In general each corneule
is thicker than it is broad, and thicker at its middle than at its cir-
cumference ; a layer of pigment here insinuates itself into the inter-
spaces between the corneules. In bees and flies fine hairs project from
these interspaces, which must defend the eye or w arn the insect against

INSECTA. 213

the approach of foreign bodies. Each division of the compound eye
has its lens, which combines the characters of both crystalline and
vitreous humours : it is always of a more or less elongated conical
form, having its base applied to the corneule^ and its apex to the optic
nerve. The base is not immediately in contact with the cornea, but
is separated by a minute aqueous chamber into which a process of the
pigmental membrane penetrates, leaving a small pupil opposite the
middle of the base of the lens. The pigment is continued along the
crystalline vitreous cone to its apex, forming a sheath around it, and
enveloping also the adhering filament of the optic nerve; at once
separating and connecting together the component ocelli of the com-
pound eye. Fine tracheal ramifications have been traced upon the
pigment, which displays very various, and often brilliant or metallic,
hues in its outer layer.

The larvae of the Coleoptera, Lepidoptera, Neuroptera, some Hy-
7nenoptera, and Diptera, have merely simple eyes. Two or three of
such ocelli are retained, with the superadded compound eyes, in all
the preceding orders save Coleoptera, in which only compound eyes
are present in the perfect state.

The high degree in which the power of discerning distant objects
is enjoyed by the flying insects corresponds with their great power of
traversing space.

The few exceptional cases of blind insects are all apterous, as the
Claviger, and often peculiar to the female sex, as in the glow-worm
and cochineal insect.

CViM^'

X

LECTURE XYII.

INSECTA.

The extraordinary powers of locomotion possessed by insects, the
variety of elements which they can traverse, their aptitude to gain
access to every situation where organised matter may be obtained,
prepare us to expect that they should manifest all the modifications
of the digestive system which may be required for the assimilation
of the different kinds and conditions of the solids and fluids of plants
and animals.

One insect preys upon another; pursues and attacks, like the

p 3

214 LECTURE XVII.

falcon, on the wing ; but, with better mastery over the air-element,
it can tear to pieces and devour its prey without alighting. Another
insect, sedentary and inactive, imbibes the juices of a plant ; a third
eats its way into the hard wood ; a fourth burrows in the earth for
roots or worms.

Some traverse the surface of the earth with a succession of steps
too swift for definition ; some by leaps so extraordinary, as to have
excited the powers of the dynamical calculator from the earliest
periods. The waters, also, have their insect population ; some
swiftly cleaving the clear element, some gyrating on the surface,
whilst others creep along the bottom. Nor are the activities of the
aquatic insect confined to that lower sphere. The Nepa, or the
Dytiscus, at the same time, may possess its organs of reptation, of
burrowing, and of flight ; thus, like Milton's fiend, it is qualified for
different elements_, and

" Through strait, rough, dense, or rare.
With head, hands, wings, or feet, pursues its way,
And swims, or sinks, or wades, or creeps, or flies."

With such diversified powers of attaining food, there are, in fact,
associated, in Insects, equally, if not more varied, structures for
imbibing, seizing, masticating, and digesting nutritious substances.
The patience of the anatomist is taxed to the utmost to unfold these
delicate structures ; but his admiration is chiefly excited by the
discovery that they are so clearly referable to a common type.

The most marked modifications of the digestive organs relate
rather to the physical condition than the chemical constitution of the
food ; depend more upon its being solid or fluid, than upo%: its being
of a vegetable or animal nature. Some entomologists have separated
all the insects which suck the juices of plants and animals from those
which operate upon the solids, and have made the Haustellata and
Mandihulata the primary divisions of the class.

The composite parts of the proboscis or siphon are however fun-
damentally the same as those that form the strongest or most
formidable apparatus for mastication ; but as they are most con-
spicuous and most uniformly developed for the latter office, I shall
commence the demonstration of those complex parts of the mouth, —
the trophi or cibarial instruments, — as they exist in a Mandibulate
insect, {fig. 100.)

Man has two jaws only, and no Vertebrate animal has more ; they
work up and down, or in the direction of the axis of the body.
Insects have also their upper and lower jaws, horny edentulous plates,
serving in many for little else than to close the mouth, and hence

INSECT A. '^15

100 a called lips; the upper one {jig. 100. a) the " la-

^^^ brum," the lower one (d) the " labium:" but they

have likewise four more complex jaws, acting upon
each other in pairs, from side to side, or trans-
versely to the axis of the body. The upper pair
of jaws (6) are called the " mandibles," the lower
pair (c) the " maxilloB." The three lo^er instru-
ments, viz. the two maxillae and the labium, are
^ ju provided with the jointed instruments of sensation,
pScfiC^ called " palpi," the maxillae, in some insects, sup-
TrophiofaMandibuiate po^'ting cach a pair of thesc appendages, which,
insect. bcsidcs their sensitive and selective offices, serve

also to seize and hold steady the alimentary substances whilst these
are divided by the mandibles and maxillas. The lower lip has a
basal joint, or " mentum," supporting a more flexible part (ligulay or
labium proper), near to the base of which the palpi are articulated.
The upper, or inner integument of the ligula, is usually developed
into a kind of tongue, which is a distinct part (lingua') in the locusts
and Libellulae. The labrum, or upper lip, is generally a simple
transverse flattened plate.

The mandibles are subject to most variety in relation to the habits
and kind of food of the insect. In texture they vary from the hardest
chitine to soft membrane. In the predatory tiger-beetles they ter-
minate in sharp hooked points, like canine teeth, and are hard enough
to pierce the firm integument of other insects. In the dragon-fly the
inner margin of the mandibles is armed with three or four sharp
laniariform processes. In some insects the upper dentations of the
mandibles'have a trenchant edge, like canine teeth ; while the lower
ones are broad and framed for bruising, like molar teeth, as in the
cock- chaffer or the locust. The maxillae usually correspond with the
mandibles in their general characters ; but the teeth, which may be
developed from their inner edge, are more uniform and delicate :
their terminal piercing hook in the tiger-beetles is movable. The
maxillaa are often clothed with short hairs.

The mandibles of the bee-tribe are simple, but strong and trenchant ;
they are most important instruments in the economy of the different
species, and are modified accordingly. The maxillae and labium are
lengthened out to form the proboscis, but especially the lingual
appendage of the latter, which has two appendages, called " para-
glossae," developed from its base, and has its upper surface and sides
beset with hairs.

In the Hemiptera both the mandibulae and maxillae are alike at-
tenuated, and prolonged into stiff' needle or lancet-shaped organs,

p 4

216 LECTUHE XVII.

which are protected by a sheath formed by the equally elongated
labium, the upper groove of which at the same time serves to conduct
the liquid food into the mouth : the maxillary and labial palpi have
disappeared ; the latter may have coalesced with, and transferred
their properties to, the labial sheath. With such an instrument
the Cicada perforates the bark of the trees on which it lives, and
exhausts their sap ; and with a similar modification of the trophi, the
bvig and flea pierce the skin and suck the juices of animals.

In the blood-thirsty Diptera, as the gnat and forest fly, the labrum^
as well as the two lateral pairs of jaws, are prolonged into lancet-shaped
organs, and are sheathed in a thickened lower lip, which is terminated
by two fleshy suckers : the maxillary palpi are attached to the base
of the maxillee.

The singular spiral " antlia " of the butterfly and other Lepido-
ptera is formed by the elongated slender maxillae, still characterised
by the minute palpi at their base. The inner margins of the max-
illae are concave, and the edges of the channels are in close contact,
or are confluent, so as to form a canal along which the juices of
flowers can be pumped up into the mouth. Each maxilla is likewise
hollow, and it is uncoiled or coiled by the varying tension of this
canal. The labial palpi are of large size, and defend the antlia when
it is retracted and coiled up. The labrum is a small triangular
piece, which bends down towards the mouth, and the rudimental,
conical, slightly bent mandibles are hidden by the labial palpi.

The large curved piercing jaws of the Centepede are hollow, and
traversed by the duct of a poison-gland.

The alimentary canal is most simple in the larvae of insects, in
which, as in worms, it usually extends, without convolutions from
one end of the body to the other; in a few larvae, as that of the bee,
it has only the anterior opening or mouth, and the opposite or anal
orifice is not developed until the pupa-state. In all mature insects
the alimentary tract presents the two distinct apertures ; it is simplest
in the carnivorous larviform Myriapods ; presents more numerous
and distinct constrictions and divisions in the Hexapods, and increases
in complexity and length, as the food requires most preparation in
order to its conversion into the animal nutrient fluid or chyle.

The oesophagus of the Centipede is long, and dilated posteriorly,
where it communicates with the stomach ; this is a small muscular
cavity, bent upon itself, and lined by a longitudinally plicated horny
membrane. The intestine is long, straight, and wide, slightly saccu-
lated transversely ; it contracts, and is longitudinally folded near its
termination. In the lulus a short and wide oesophagus expands into
a shorter and wider muscular stomach. This is succeeded bv a lonfi

INSECTA. 217

and wide chylitic stomach, with longitudinal folds, separated by a
circular linear constriction, in the posterior third of the body, from
the intestine : this is divided by a second constriction into two
equal parts, the first longitudinally folded like the stomach, the last
puckered into short transverse sacculi ; until w ithin a little distance
of the anus, which is protected by a pair of horny valves.

In the Polydesmus the oesophagus gradually expands into the long
chylific stomach, which is separated by a short contracted pyloric
tube from the intestine. This suddenly swells out to equal width with
the stomach, is puckered up in its posterior half by short transverse
plicae, where it first gradually, and then suddenly, contracts to termi-
nate at the anus.

The accessory glands of the digestive tract are slender tubes in the
Myriapod, as in the Hexapod tracheary Insects. In the Polydesmus
and lulus there are two such salivary glands at the sides of the oeso-
phagus, converging anteriorly to open into the pharynx. The more
compact and similarly situated poison glands, which terminate in the
large perforated hooked mandibles, in the Centipede, are superadded
to the simpler salivary glands of the Chilognatha.

Slender biliary tubes creep upon the intestinal tunics in the Centi-
pede^ and pour their secretion into the canal close to the gizzard.
Excretory, probably urinary, tubes open into the terminal division
of the intestine ; and these are present in the lulidee.

The alimentary tract in Hexapod Insects is divided into pharynx,
oesophagus, ingluvies or crop, gizzard, chylific stomach, small intes-
tine, caecum and rectum. All these parts rarely co-exist in the same
insect. The oesophagus is directly continued from the sucking ap-
paratus in Haustellate Inse"cts without a pharyngeal dilatation.

In the carnivorous Dragon-fly * the alimentary tract is short and
straight: there is neither crop nor gizzard, the chylific stomach is
long, cylindrical, and is divided from the oesophagus by a slight con-
striction ; the short intestine which succeeds is dilated at its com-
mencement, and plicated longitudinally as far as the contracted
rectum. In other insects a duodenal and iliac tract of intestine may
be distinctly recognised. In the tiger-beetle {Cicendela) and the
carnivorous Carabidce^ there is a small gizzard, preceded by the usual
ingluvial dilatation of the oesophagus and followed by a long
chylific stomach, the external surface of which is beset with secerning
follicles. The small intestine makes a short turn before terminating
in the dilated colon.

The alimentary canal of the browsing cockchafer is considerably

* Prep. No. 589.

218

LECTURE XVII.

longer, and is disposed in three or four coils. But in the Orthopterous
vegetable-feeding insects^ the canal is characterised by its superior
width rather than by its length ; and in them the complications re-
quisite for animalizing the food are chiefly manifested by the gastric
division. The oesophagus dilates into a wide glandular crop in the
cockroaches* and locusts-]-, and has a similar receptacle appended
to it in the mole-cricket. J The gizzard has a strong muscular coat,
and a callous epithelium, the inner surface of which is beset with
projecting teeth or hooks, as in the cock-roach, or with scale-like
plates, as in the cricket, generally disposed in longitudinal rows. The
tunics of the chj^lific stomach are produced at its commencement into
caecal appendages, which augment and complicate its cavity. There
are two such caeca in the common and mole-crickets, four in Locusta
serratUj six in the migratory locust, and eight in the cockroach. In
the coleopterous Buprestidce the stomach is prolonged into two caecal
appendages, themselves beset by smaller caeca.

The gizzard always coexists with the crop, but not always the crop
with the gizzard, in insects. All the suctorial species have a crop,
either appended to the oesophagus, or forming a preliminary dilata-
tion to the chylific stomach. It is of small size in the bug (^Cimex
lectularius), and almost obsolete in other Hemiptera. In the bee,
{fig. 101.) §, the oesophagus (a), having tra-
versed the thorax as a slender tube, dilates in
the abdomen into the large honey-bag {b).
The valvular funnel-shaped orifice of the chylific
stomach (c) projects into the side of the inglu-
vial reservoir, and must be withdrawn by a
special action, in order to receive any portion
of the nectar for the nourishment of the bee
itself: it then returns by an antiperistaltic
motion, and forms a kind of intussusception in
the crop, converting it into the convenient, closed
Alimentary canal. Bee. j-eccptacle for the Collected swccts until the bee
reaches its hive ; when the honey, having undergone a slight change,
which renders it less susceptible of the acetous fermentation, is
regurgitated into the waxen cell, and the crop collapses into lon-
gitudinal folds. The chylific stomach (<:/) is long, gradually widened
to its termination, and transversely plicated. The ileum (e) is short
and slender : the colon or rectum (/), wide and capable of great

* Nos. 607, 608, 609.
\ No. 611.

f Nos. 443. 610.
§ Nos, 476, 477.

INSECTA. 219

distension. The bees on which Hunter experimented* endured a
long confinement, but could not be compelled to foul their hive ; as
soon as liberated, they rose in the air and disburthened their over-
laden cloaca.

In the Lepidoptera i^fig' 105.), the ingluvies projects, like a bag,
from the side of the oesophagus {j) ; and in the Zygcence. it is divided,
as in the pigeon, into two equal parts. The chylific stomach is very
small, but is sacculated, and, according to Meckel, is shaggy in the
death's-head moth. The small intestine (/) is longer and more con-
voluted than in the bee ; the large gut (m) is short and wide.

In the Diptera the cropf, though situated upon the stomach in
the abdomen, is appended by a long and slender neck to the be-
ginning of the narrow oesophagus. The lower end of the oesophagus
expands into the chylific stomach, the cardia being sometimes marked
by a callous ring, which is the remnant of a small bladder existing there
in the larva. The small intestine is convoluted ; the rectum short
and dilated, and provided with two lateral conical glandular bodies. \
Hunter made experiments to determine the function of the appen-
diculated crop. " I kept a fly," he says, " for twelve hours without
food, and then gave it milk and killed it, and found no milk in the
crop, but it had got through almost the whole tract of intestines :
here the animal had immediate occasion for food, therefore the milk
did not go into the crop. This experiment at the same time shows
that every part of the intestine digests." Another time Hunter killed
his flies after they had drunk their fill, and found the crop full, as
well as the stomach and intestines : he suspects, therefore, that the
crop serves as a reservoir, and " that when there is more food than
what is immediately necessary, then it is thrown into the crop to be
used in future." §

The result of Hunter's first experiment, and the absence of the
crop in the flea and some other suctorial insects, negative the idea of
Burmeister that the crop in Hymenoptera, Lepidoptera, and Diptera
promotes the suction of food by a voluntary power of self-expansion,
if even the structure of the part justified the idea ; but, on the con-
trary, they prove it to be a receptacle of nutriment.

In the Cicadae the chylific stomach is of great length, intestiniform,
and its termination is connected, but does not communicate, with its
commencement ; the chymified fluids pass at once from its termi-
nation into the intestine.

The entire alimentary canal consists of three tunics, an external

* See Philos. Trans. 1792. p. 176.

t No. 596. \ No. 2123.

§ Physiol. Catalogue of Hunterian Collection, vol. i. p. 1 89.

220 LECTURE XVII.

fine membraneous, or peritoneal layer, a compact muscular mem-
brane, and an internal mucous or epithelial coat. Between the last
two there is a white spongy layer of cellular tissue, compared by
Ramdohr to transuded chyle, and which is sometimes the seat of
gastric glands.

The several divisions and convolutions of the alimentary canal are
supported and attached to the adjoining parts by the air-vessels :
there is no mesentery.

At least three kinds of glands add their secretions to those of the
caeca and follicles of the alimentary canal. The first kind open in or
near the commencement of the canal, and are regarded as salivary
glands. They are classified by Professor Burmeister as follows : —

A. Salivary vessels which open into the mouth, generally beneath
the tongue, sometimes at the base of the mandibles. They take the
following forms : —

1. As simple, long, undivided, twisted tubes ; thus in the majority
of insects, viz. all butterflies, many beetles, and flies.

2. As a narrow vessel which empties itself into one or two
bladders, whence the salivary duct originates {Nepa, Cimex^ Sarco-
phaga).

3. As a ramose vessel with blind branches (Blaps).

4. As two long cylindrical pipes, which unite into one excretory
duct (Heduvius).

5. As four small, round bladders, each pair of which has a common
duct (^Pulex, LygcBus^ Cimex).

6. As a multitude of such vesicles (Nepa).

7. As capitate tubes, in the free ends of which many very fine
vessels empty themselves ( Tabanus).

8. As tubes which at intervals are surrounded by spiral caeca
( Cicada).

9. As granulated glands, which on each side unite into a salivary
duct, both of which join into a single excretory duct. Muller has
observed this high form of conglomerate salivary glands in Phasma ;
Treviranus in Apis; and Burmeister in Locusta, Gryllus, and
Termes.

The biliary secerning organs never attain this condition, but, in all
insects, manifest the condition of long^ slender, cylindrical tubes,
which Cuvier, who seems not to have been aw^are of the conglomerate
structure of certain salivary and seminal glands, describes as the
character of all the secreting organs in insects.

In a few instances, as in Chermes and Aphis, the biliary tubes are
wanting: in almost all insects they are four in number, never fewer;
sometimes they are six or eight in number : in a few instances, as the

INSECTA. 221

mole-cricket and cockroach, they are very numerous. Dr. Burmeister
has generalised the observations of different anatomists on the bile-
tubes, as follows : —

1. Four.

a. Free at the end ; most Diptera, and the families Termi-

tina, Psocina, and Mallophaga.
h. Anastomosing ; many Coleoptera, Hemiptera^ and Diptera.

2. Six biliary vessels.

a. Anastomosing ; many Coleoptera ; for example, Ceram-
hycina and Chrysomelina.

b. Free at the end ; Lepidoptera.

3. Eight free biliary vessels ; Neuroptera.

4. Many biliary vessels ; Hymenoptera, Orthoptera, and the Dic-
tyotoptera subulicornia.

Those biliary vessels are longest which are fewest in number : they
lie in folds by the side of the stomach and intestine, and terminate in
a circle at the commencement of the small intestine. In LygcBus
apterus they terminate in a dilatation on one side of the gut.

The urinary glands are usually in the form of long and delicate tubes,
but sometimes present the structure of groups of round vesicles, as
in the Carabiis, in which the common duct terminates in a small
dilatation : the urinary bladder is likewise present in the water-
beetles. The excretion is poured into the termination of the in-
testine, or evacuated contiguous to the anus.

No absorbent vessels have been detected in msects ; the chyle,
which is a clear or greenish fluid, with round or oval corpuscules, is
supposed to transude through the tunics of the intestine into the
free cavity of the abdomen : it passes, in reality, into the wide and
irregular sinuses which seem to constitute the cavity of the abdomen,
but which communicate with similarly ill-defined venous receptacles
extending into other parts of the body and its appendages, resembling
the general interspaces of the cellular tissue, and constituting the
venous system, through which the blood moves in a definite and regular
course to the heart. This organ {Jig> 104. s) is an elongated muscular
and valvular tube, situated along the middle of the back, and usually
called the dorsal vessel : it is largest in the abdomen, and so dimi-
nishes anteriorly, that its continuation in the thorax may, in most
insects, be regarded as the aorta. It is retained in its position by
flattened triangular bands of muscular fibres. This character, its
distinct transverse linear muscular fasciculi, its slight constriction at
regular intervals, and the peculiar valvular loops at these constric-
tions, characterise the long and slender vasiform dorsal heart in the

222 LECTURE XVII.

lulus and Scolopendra, and indicate its great advance beyond the
condition of the dorsal artery in the Anellides.

In the perfect Hexapod Insect, the heart has the appearance of a
series of slightly conical segments, partially sheathed one upon the
other: lateral apertures exist at the sides of the intus-susceptions,
where, in fact, valvular folds of the inner tunic do project into
the interior of the heart, and partially divide its cavity into so
many separate chambers. The whole of this part of the heart is
included in a saccular venous sinus, from which the blood passes into
the interior of the heart, and, by the disposition of the valves, it is
at once prevented from returning into the sinus, or passing in any
other direction in the heart than towards the head, or into the next
chamber in advance of that by which the fluid was admitted. The
number of venous orifices varies in different insects : — in most species
there are eight pairs of apertures ; in the stag-beetle there are six
pairs ; in the humble-bee five pairs ; in the phasma there is, according
to Miiller, only a single pair at the posterior chamber of the heart,
by which, in fact, in all Insects, the chief currents of the blood
appear to enter the organ. As far as the head the blood is propelled
from the heart along a tubular aorta of the usual form ; but the
branches from this would appear soon to lose themselves in the
generally diffused sinuses. In the Myriapoda, however, the blood is
continued in a vessel along the dorsal aspect of the ventral nervous
chord ; but the traces of the true tubular vascular system are scanty
and obscure.

Cuvier, misled by the anomalous diffused condition of the venous
system, supposed that there was no circulation of the blood in Insects ;
yet the dorsal vessel was too conspicuous a structure to be overlooked.
Such, however, was the authority of the great anatomist, that the
nature of the heart began to be doubted, and the strangest functions
to be attributed to it. Hunter, however, who was prepared to ap-
preciate the true state of the circulating system in insects, by his
discovery of the approximatively diffused and irregular structure of
the veins in the Crustacea, has described in his Work on the Blood *
all the leading characters of the circulation in Insects as it is recog-
nised by Comparative Physiologists of the present day. He says,
that, " As the lungs of the flying Insect are placed through the whole
body, the heart is more diffused, extending through the whole length
of the animal ; " that " where the veins near the heart are large, there
is no auricle, as in the lobster and generally in insects;" that " in
the winged Insects, which have but one heart, as, also, but one cir-

* Quarto, 1794. p. 220. et seq.

INSECTA. 223

culation, there is this heart answering both purposes" (viz. the cor-
poreal and puhnonary circulations) ; and again, " with respect to its
use, it is, in the most simple kind of heart, to propel the blood through
the body, immediately from the veins, which blood is to receive its
purification in this passage, when the lungs are disposed throughout
the body, as in the flying Insect." In the note at p. 221. he alludes
to the animals in which the veins are entirely cellular ; and expresses
his idea more definitely in the following passage from his manuscript
Observations on Insects: — " Of the veins. The veins of the Insect would
appear to be simply the cellular membrane ; but they are regularly
formed canals, although not so distinctly cylindrical canals as in the
quadruped, &c., nor branching with that regularity. They would
appear to be, or to fill up, the interstices of the flakes of fat, air-cells,
muscles, &c., and therefore might be called in some measure the
cellular membrane of the parts." *

The chief merit of the rediscovery of the circulation of the blood
in Insects is due to Carus; its phenomena have been witnessed in
the appendages of Insects by other observers, as Ehrenberg, Wagner,
Burmeister, Bowerbank, and Tyrrell. Hunter counted thirty-four
pulsations in a minute in the heart of a silkworm. Herholt counted
from thirty to forty pulsations of the heart in a minute in a full-
grown caterpillar : Suckow observed thirty per minute in a full-
grown caterpillar of the pine moth, and only eighteen in its pupa
state.

The action of the heart is accelerated in Insects, as in other
animals, by muscular exertion and excitement ; and Mr. Newport has
counted as many as 142 pulsations in a minute, in a species of wild
bee so excited.

Although the anatomist searches in vain for that profusion of ar-
terial and venous vessels which pervade the body of most animals,
the insects are not without their systems of capillary tubes, which
ramify as richly over all the organs and through every tissue, and
which connect together the different parts of the body. These ves-
sels, however, carry air instead of blood ; the relations between the
sanguiferous and respiratory systems are reversed, and the air is dis-
tributed by a vascular system over the reservoirs of blood, instead of the
blood being distributed by a capillary net- work over a reservoir of air.
The aeriferous tubes in insects are called " tracheae," having their
parietes strengthened by an elastic cartilaginous filament, not indeed
disposed in a series of distinct rings, but in a continuous close spiral
coil. By this structure the most delicate and invisible ramifications
of the air-tubes may be easily recognised under the microscope. The

* Physiol. Catalogue, vol, ii. p. 31.

224

LECTURE XYII.

spiral filament is situated between the external cellular, and an in-
ternal delicate epithelial lining.

The trachese commence either from lateral apertures, called spi-
racles and stigmata {fig. 102.
/), or from pneumatic tubes
{i\ generally continued from
the anal segment ; these latter
are peculiar to insects which
live in water, as the Nepa
and Ranatra.

The air is conducted from
the spiracles or the pneumatic
tubes, both which may co-
exist together, into a large
longitudinal tracheal trunk
(<7), which runs near each side
from one end of the body to
the other; they are connected
together by transverse tubes,
which run across the posterior
margin of each abdominal
segment, and distribute an in-
finitude of smaller tracheal
ramifications. Some of these
branches dilate into air re-
ceptacles (/i), the number and
size of which, like the air-cells
in birds, are in direct relation

Respiratory system, Nepa. vvith the pOWCrS of flight. In

the Nepa these reservoirs of air are confined to the thorax : in other
insects, as the grasshopper, they are frequently developed also upon
the transverse abdominal tracheae : they are very capacious in the
abdomen of the bee.

The spiracles differ in number and form in difi'erent insects. In
the Coleoptera there is a spiracle at the interspace between every two
segments ; the Diptera have the fewest spiracles. In some insects the
orifice is situated upon an entire oval horny ring- In many insects,
especially those that burrow, the margins of the spiracles are de-
fended by a fringe of hairs, which prevent the entry of extraneous
particles. In the mole-cricket, the thickened margin of the spiracle is
strengthened by two horny half rings, and can be closed by the
action of the small sphincter muscle.

Most of the aquatic larvae breathe by temporary gills ; in the Phry-
ganeae these consist of vascular laminae developed from each side of the

INSECTA. 225

upper part of each abdominal segment ; in the Semblidae plumose
branchiae are similarly situated.

The amount of respiration is directly as the degree of the activity
of the insect ; and its temperature is increased in an approximate de-
gree. The extraordinary development of the breathing organs de-
monstrate their essential relations to the energies of the muscular
system ; and, by a minor modification, they are made subservient to
the diminution of the weight of the insect. In the Apterous insects,
and especially the Myriapoda, there is no trace of air vesicles, but
both in the Centipede and lulus the minute tracheae ramify throughout
the body.

LECTUEE XVIIL

INSECTA.

The sexes are distinct in all Insects : in certain social species, as
bees and ants, there is a third kind of individuals, commonly called
neuters, but these are essentially females with the organs imperfectly
developed and passive.

In the Centipede the testes are small, slender, fusiform bodies,
placed one behind the other in the dorsal region of the posterior part
of the body : four pairs and an odd one are on the left side, and three
pairs on the right. A minute efferent tube is continued from both
ends of each testis, which tubes unite with those of the adjoining
organ, and ultimately form a single vas deferens, common to the two
lateral series of testes, and situated along the middle of the body : it
forms a kind of epididymis by its zig-zag convolutions, and, after
having received the ducts of three pairs of small prostatic glands, it
terminates in the cloaca.* In the lulus the external openings of the
male apparatus are situated upon a small protuberance behind the
seventh pair of legs.

In the Hexapod Insects the testes usually present a more compli-
cated structure, but are almost as diversified in the form, number, and
disposition of their secerning follicles as the stamens of plants. They
present their most simple condition in the Lepidoptera, in which they
approximate during the metamorphosis, and unite into a single globular
mass, the primitive separation of the two testes being indicated by a

* Prof. R. Jones and Straus Durckheim.
Q

226 LECTURE XVIII.

circular indentation and by the two distinct vasa deferentia. In
certain moths, as the Tiiiea, the original condition is retained in the
imago state. The vasa deferentia and tubular glands are extremely
long and convoluted tubes.

In the male Aphis three, four, or five spherical testes communicate
by short tubes with a common transverse duct, the two extremities of
which bend down and complete the circle by uniting to form the short
ductus ejaculatorius. A long pyriform vesicular gland is appended
to each lateral vas deferens.

In all other insects the testes form a pair of white glandular
bodies : in the dragon-fly they are elongated and fusiform, as in the
Centipede. In the Cercopis each testis is a clavate gland, gradually
contracting to the vas deferens. In the crane-fly ( Tipula) the testis
is a convoluted filamentary tube, dilating into a vesicle before it is
continued into the vas deferens : in the Ranatra the tube is twisted
spirally. In the Dytiscus the testis is a filiform tube, much longer
than the abdomen, but convoluted into a round ball. In the Hydro-
philus, a series of short blind processes are given off from one side of
a common duct. In the Buprestis a fasciculus of longer caecal tubes
radiate from the end of the sperm duct. Sometimes the extremities
of similar radiating tubes are dilated into saccular flattened glands,
as in the rose-beetle {Cetonia), and numerous more composite forms
have been detected ; all, however, are referable to modifications of
the primitive blind secerning sac. Their analogy to the sexual parts
of plants has already been alluded to, and Entomologists have found
it requisite or advantageous to borrow the neat and descriptive terms,
with which Linnaeus has enriched botanical science, in order to indi-
cate the diversified forms of the male apparatus.

The vasa deferentia always receive the ducts of glands which are
analogous to the vesiculse seminales ; these are generally formed of
slender tubes, not exceeding the length of the abdomen in the
Lucanus, Locusta^ and Libellula, but five times longer than the body
and much convoluted in Dytiscus, ten times as long as the body in
Blaps, and thirty times as long in the Cetonia aurata. The sperm-
duct is dilated where it receives the secretion of the accessory glands,
as in the bee. In many insects,, representatives of prostatic glands
communicate with the ductus ejaculatorius.

The intromittent organ is a modification of the last or two last
segments of the abdomen, and is usually retracted out of sight : it
consists of a large exterior sheath and a delicate membranous tube :
the sheath commonly consists of two lateral valves. Accessory pre-
hensile organs are developed in some insects, of which the most
remarkable are attached to the base of the abdomen in the male
Libellula.

INSECTA.

227

103

Noctua Brassicae.

The female sexual organs {fig. 103.) consist of the ovaries (a, «), the
oviducts, the uterus {g), the spermatheca (6), the mucous glands (e),
and vagina ; but these are not all present in all insects. The external

organs are the vulva, the sting, the
holders, and ovipositor, some of which
are likewise peculiar to particular
species.

The most constant and essential
parts of generation of the female in-
sect, viz. the ovaria, are subject to
almost as many varieties as the testes
in the male ; their forms may be ar-
ranged into almost as many genera
and species, which are very often
analogous to those of the essential
glands in the opposite sex. Teh ovaria in the Lepidoptera do not,
however, coalesce into a single mass^ like the testes in the male :
they are either digitate or verticillate ; that is to say, they consist
of a few egg-tubes suspended to the end of the oviduct, be-
coming attenuated as they recede from it; or they consist of nu-
merous very long egg-tubes, proceeding from a short oviduct and
terminating in filiform extremities : they are usually disposed in
spiral coils bending at the two sides in opposite directions, as in the
Noctua BrassiccB. In the forest-fly each ovarium consists of two
egg-tubes ; in the flesh-fly it consists of a single tube, which is of
great length, and twisted spirally. In the mantis a single series of
short egg tubes are attached to one side of a common duct. In the
gnats, crickets, and locusts, the numerous egg-tubes, which are some-
what compressed, lie upon one another like scales, or the tiles upon a
roof. In the Ephemera and Stratiomys, the ovaries have the primitive
form of simple elongated bags in which the eggs are contained linked
together by delicate filaments.

In the plant-louse (Aphis) the ovaria consist of eight short and
straight tubes continued from a very short and w ide oviduct : the an-
terior capillary beginnings of the ovarian tubes are composed of a
single file of nucleated cells. From these a distinct canal is con-
tinued for a short distance, which dilates into a sac filled with numerous
other nucleated cells ; a second constriction separates it from another
dilatation containing a more definite group of nucleated cells forming
a vitelline mass, presenting sometimes an elongated or larviform
figure ; the ovarian tube then dilates into an elongated wide receptacle
in which the development of the larva is completed in the apterous and
larviparous females, which produce their young during the spring and

Q 2

^28

LECTURE XVIII.

summer months. In the autumn the organs are somewhat changed
in form ; the terminal ovarian portion dilates into a clavate ccecal
extremity filled with numerous ova : the rest of the straight canal is
divided into two successive elongated elliptical chambers, the last
being the largest, and generally containing an elongated ovum which
is excluded as such.

The fertility of an Insect is indicated by the length and number
of the egg-tubes. Seventeen ova have been counted in a single tube
in the queen-bee, which has more than a hundred of such tubes.
But her fertility is greatly surpassed by the queen of the Termite
communit}^ in which the abdomen expands to so enormous a bulk, in
order to include the ovaria, that the thorax and head seem like mere
appendages to its anterior part. She lays, according to Smeathman,
sixty eggs in a minute, and this rate is continued, with, perhaps,
intervals of repose, for several days.

However various may be the form and structure of the ovaria, their
situation is nearly the same in all insects. They occupy the sides of
the abdomen, and, when fully developed, distend that cavity, leaving
space only for the intestine and the internal accessory parts of gener-
ation. They are connected together by the branches of the tracheae,
and, in many insects, are retained in their position more particularly
by delicate but firm filaments continued from the anterior extremity
of each ovarian tube, and ascending to become connected with the
thoracic aorta. Professor Miiller describes these filaments as opening
into the dorsal vessel.

The oviduct varies in length and capacity : in the Hydrophilus
four filamentary blind canals are attached to each side ; but in most
insects the accessory glands communicate with the common canal
formed by the union of the two oviducts. The common canal has
usually a dilatation at its middle part, beyond which it receives the
tube of the spermatheca and the duct of the coUeterium or mucous
vesicle.

Experiment has proved the office of the spermatheca {fig. 103, 6.)
to be that which its name implies.* By the application of the fluid
contained in it to the eggs of an unimpregnated female Hunter made
them fruitful : he also found that the intromittent organ penetrated
its canal, an observation which has since been confirmed by Andouin,
and other observers.

The coUeterium i^fig' 103, c.) secretes the white gluten, with which
the impregnated eggs, when not developed in the body, are covered,
and by means of which they are cemented together and fastened to
other objects. In some insects, as the Tinece^ the mucous organ has the

* See Hunter, Animal Economy, 8vo, 1837, p. 461.

INSECTA. 229

simple tubular form ; in the Meloe it is a vesicle furnished with a short
neck ; it is a large ovate bladder in most of the Lepidoptera, as in
Jig. 103. In the stag-beetle there are two mucous vesicles, the short
ducts of which unite into a common tube. In the Elater murinus
the colleterium bifurcates repeatedly, and the base of each fork dis-
tends into a triangular bag.

Accessory filamentary tubes are met with in several of the butter-
flies. Certain social Hymenoptera, which, as John Hunter quaintly
observes, " have property to defend," possess a peculiar poison appa-
ratus, which is essentially a modification of accessory parts of the
female organs, and the only part which reaches its functional activity
in the neuters of the Bee and Wasp. The poison is secreted by two
long and slender ducts, which unite together and empty their secretion
into an oblong bag, which discharges itself by a narrow duct between
the valves of the sting. This is a long, slender, and sharp process,
with a serrated edge, which generally prevents its retraction when
thrust into the skin : the protecting valves are modifications of the
last abdominal segment.

The corresponding parts are variously modified in other insects to
insure a proper deposition of the eggs. In some insects, as the Locusta
viridissima, the bivalve ovipositor is longer than the body, and by
means of it, the ova are conveyed to the proper depth in the soil, the
act of oviposition being precisely analogous to that of setting seeds in
the earth. In the saw-flies, a third organ, analogous to the sting in
bees, and similarly serrated, is superadded to the ovipositor : with this
instrument the female saw-fly (Tenthredo) saws into the substance of
leaves, and there insinuates her eggs. The Ichneumons have a similar
apparatus, but extremely elongated and slender, by means of which
they introduce their ova beneath the skin of other insects.

Insects, like Crustaceans, are occasionally subject to one-sided or
dimidiate hermaphroditism. Numerous instances of this kind are
given by Ochsenheimer. In fourteen of the above cited instances, the
right side was male and the left female : in nine instances it was the
reverse. Occasionally Hermaphrodites are found, where the characters
of one sex, instead of extending over one half, are limited to particular
parts of the body, which agrees in the main with the other sex. Thus
an individual of the Gastrophaga Quercus has been observed, in which
the body, the antennae, and the left wings were those of the female,
the right wings those of the male. The external sexual characters are
very striking and various in the class of Insects, and readily lead to
the detection of the hermaphroditical condition of the internal organs.

The development of an insect commences, as in all other animals,
from a. minute pellucid vesicle, having a central nucleus or spot,

230 LECTURE XVIII.

Such vesicles make their appearance in the capillary beginnings of
the ovarian tubes, where they are drawn out to microscopic tenuity.
From these extremities the ova successively pass into the wider part
of the tubes, and in this course increase in size by the multiplication
of vitelline cells around the primitive vesicle : at first the ova are
separated from each other by an amorphous granular substance of
equal size, which is called a placentida, but lower down by mere con-
strictions of the egg-tube : here they acquire a distinct vitelline mem-
brane, and then, still continuing to increase in bulk, by the progressive
addition of that material which is afterwards to be expended in forming
the tissues of the future insect, they reach the termination or con-
verging point of the ovarian tubes, and enter the shorter and wider
oviducal track : here they receive additions to their external surface
from the collateral and accessory glandular organs, and admit into
their interior the mysterious principle of the male fluid, which would
seem to be assimilated into their substance.

In this state the ova are excluded in most insects ; but there are
some species, as the common flesh-fly (Musca vomitoria), in which de-
velopment proceeds, prior to the exclusion of the ovum, to an extent
equivalent to the acquisition by the embryo of the form and condition
of the young of the viviparous entozoa ; the formative processes
closely according with those which have already been traced, at p. 77.,
in the Ascaris acuminata. The sub-divided and hyalinized cells of the
yolk have arranged themselves into the form, and have been trans-
muted into the tissues, of a worm, — a worm which, coming from the
^%% of an insect, is termed a grub, maggot, or larva. In a few other
insects, again, this stage of intra-uterine development is brief and
transitory, a merely passive, embryonic stage, which is left for a
second one, commencing by the formation of the head, by a slight
excess in the growth of the first three segments of the trunk, and the
budding forth from these of rudimental limbs ; the head is then fur-
nished with eyes, antennae, and trophi, the wings are developed, and in
this state, inclosed in the exuvial skin of the larva, and ready to issue
from it as the perfect insect, the young of the forest-fly are brought
forth. The process is termed pupiparous generation : the more pre-
mature production of the flesh-fly is called larviparous generation.
By far the largest proportion of the class of insects^ as I have already
said, is oviparous ; and the development of the embryo takes place
out of the body of the parent.

There are many striking and beautiful manifestations of instinctive
prescience in the modes of oviposition, and in the location and at-
tachment of the ova. Many insects not only provide the germ
M'ith the nutritive vitelline mass, or the material for the first develop-

INSECTA. 231

ment of the embryo (if, indeed, the parent can be said to be concerned
in that supply which is the result rather of a series of spontaneous
fissions with an inherent power of assimilation of the primitive germ
itself), but, in some cases, the parent, having selected a fit place for
the deposition of her precious burthen, continues the maternal office
by placing near the ovum the kind of food which the larva will neces-
sarily require in order to complete its growth.

Some insects, as bees and ants, feed the larva; supply them with
the required food from time to time, as nurses satisfy the cravings of a
child; bat these cares rarely devolve upon the mother in the insect class:
they are performed by a distinct race of individuals, of the feminine
sex, but incapable themselves of exercising the procreative faculty.

The forms of the eggs of insects are very variable ; often beautiful
and regular, like the seeds of plants ; sometimes very singular ; always
perfectly adapted to the required conditions for the development of
the future insect. The eggs are cylindrical in Bomhyx everia ;
conical, with tuberculate ribs, in Pontia napi ; hemispherical in
Bomhyx dumeti ; lenticular in Noctua psi ; cup-shaped in Orgyia
antiqua ; flask-shaped in Culex pipiens ; petiolate in Hemerobius
perla; provided with diverging processes like ears in Scatophaga
putrisy to prevent their sinking too deep in the soft dung ; provided
with a special adaptation for floating in some aquatic insects ; with
numerous other modifications.

When embryonic development begins, the vitellus becomes con-
densed, as in the Ascaris, receding a little from the vitelline membrane
at its poles. The usual processes of subdivision take place, but in
so much greater a degree at the peripheral layer that the subdivided
vitelline mass becomes invested by a stratum of minute and nucleated
cells. Kolliker, who has observed these early stages of insect deve-
lopment in the Chironomus tricinctus Schrank, gives the following
account of the process. The primordial cells, at first round, and
provided with one nucleolus, become afterwards elliptical, and ge-
nerally two nucleoli can be discerned in them ; afterwards two cells
exist, of smaller size than the parent cell. He concludes that this
fissiparous generation of cells, which accords with that observed by
Siebold and Bagge in the Ascaris, is the general mode of their mul-
tiplication. " Haec omnia, etsi nunquam cellulas in aliis inclusas
off'endi, ne ad sententiam adducunt, posteriores a prioribus gigni, ita
semper binae in unaquaque cellula matre oriantur." *

The vitelline mass becomes elongated and vermiform, and, by
farther subdivision and coalescence of the peripheric stratum of cells

* Observationes de prima Insectorum Genesi. 4to. Turici. 1 842.
Q 4

232 LECTURE XVIII.

(*' cambium " of Herold), a smooth transparent integument is formed,
like that in the Entozoon, first along the ventral aspect, then ascend-
ing up the sides to the dorsal aspect, which is likewise closed in by
the reciprocally approximating folds which cover the cephalic and
caudal extremities. The division of the integument into the thirteen
segments commences at the ventral aspect, which is convex, the ver-
miform body of the embryo being, at first, bent upon the back.

In the capitate larvae the entozoal type is quickly left by the cer-
vical constriction, and the development of a distinct head, which
commences by the formation of the part afterwards retained as the
labrum. The mandibulse and antennae next appear behind the
labrum as convex lobes ; and the part of the head in the lower in-
terspace of the mandibles forms the labium. The maxillae next bud
forth between the labium and the mandibles, and the median fis-
sure, surrounded by the rudimental trophi, sinks deeper into the
substance of the head, and, meeting a slender anterior production
of the internal vitelline sac or cavity, establishes the mouth and
oesophagus. Whilst these stages are in progress^ the peripheral
series of included vitelline cells have undergone a series of spon-
taneous fissions ; whereby the remaining mass becomes included
within a second stratum or cambium, which, by coalescence and
further metamorphoses of the cells, is transformed into the tunics of
the alimentary canal, the interspace between which and the outer
integument forms the abdominal cavity. A certain proportion of
the vitellus^ not included in the ellipsoid alimentary canal, has un-
dergone transformations, by which the foundations of the muscular
system, the ventral nervous chord, and the dorsal vessel, are laid.
An attenuated posterior prolongation of the ellipsoid vitelline or
alimentary sac forms the rectum, and opens upon the thirteenth
segment, while it is bent upon the dorsal aspect.

In such a condition, but without the cephalic and trophal develop-
ment, the entozoiform larva of the flesh-fly is born or excluded from
the parent : in a similar condition the larva of the bee quits the vermi-
form ovum, but without the external communication with the digestive
or vitelline sac, having been established at the posterior extremity.

In some Coleoptera development proceeds to the formation of the
appendages of the head, as above described, and a capitate but apodal
larva is excluded, as in the nut-weevil.

In the other Coleoptera, as the DonacicB*, the ventral arcs of the
second, third, and fourth segments, send out bulbous rudiments of the
thoracic legs, before the tergal or notal elements of the segments are
com})leted ; the abdomen is closed above whilst the development of the

* Kolliker, loc. cit. p. 15.

insectX. 233

extremities has proceeded to the formation of obscure joints and
terminal hooks. The rudimental palpi begin to bud from the maxillae
and labium ; the mandibles acquire their hard terminal hooks, and
closely resemble the thoracic feet. In this state the larva is excluded.

At an earlier period the simple bulbous antennae, mandibles, and
maxillae, indicate three cephalic segments, equal in size and distinct-
ness to those of the thorax. The labrum and labium might perhaps
be regarded as indicative of two other abortive segments, but with
this concession not more than five cephalic segments can be defined
by observation of the early development of the insect. The biliary
and other tubular glands result from juxtaposition in a linear series
of vitelline nucleated cells, which coalesce by liquefaction of the
parts of the capsule in contact with each other, the nuclei remaining
longer and indicating the primitive separation of the cells. The
ovarian tubes have appeared to me, in the larva of the silkworm, to
retain the primitive series of nucleated cells at their capillary begin-
nings without coalescence, which has taken place to form the lower
part of the tube: such persistent, primitive, nucleated granules seem
to form the basis for the formation, by the usual fissiparous multipli-
cationj of the subsequent ova.

In the Aphides the corresponding vitelline cells retain their share
of the fecundating principle (which was diffused through the pa-
rent egg by the alternating fissiparous, liquefactive and assimilative
processes,) in so potent a degree, that a certain growth and nutritive
vigour in the insect suflace to set on foot, in the ovarian nucleated
cells, a repetition of the fissiparous and assimilative processes by
which they transform themselves in their turn into productive insects ;
and the fecundating force is not exhausted by such successive sub-
divisions, until a seventh, ninth, or eleventh generation.

This procreation from a virgin mother, this transmission of the
virtue of the ancestral coitus to the ninth generation, have hitherto
ranked amongst the most marvellous and inexplicable phenomena in
physiology. Reaumur eluded the diflficulty by afliirming the Aphides
to be androgynous ; but all subsequent entomologists deny the ex-
istence of any trace of male organs in the virgin larviparous Aphis ;
and all have recognized the distinct winged male insect. Leon
Dufour referred the phenomena to spontaneous or equivocal genera-
tion, which is independent of any impregnation. But this kind of
generation is purely hypothetical, and has been rendered less and
less probable by every successive exact observation and experiment ;
and in the Aphides the male insects are unequivocal and numerous.

Professor Morren, the latest and most exact observer of the anatomy
and habits of the Aphides, alludes to an opinion he had formerly held,

234 LECTURE XVIII.

viz. that the generation of the Aphides took place, as in some En-
tozoa, by the individualisation of a previously organised tissue.* No
one, however, has observed a portion of mucous membrane, muscular
or nervous fibre, or other organised tissue detach and transform itself
into an Entozoon ; such a process is as hypothetical and as little in
accordance with observed phenomena as spontaneous generation. The
fissiparous nucleated cells, once metamorphosed into a tissue, can pro-
duce nothing further; but those which retain their primitive state amidst
the various tissues which the rest have constituted in building up the
body of the new animal, may, by virtue of their fissiparous and assi-
milative forces, produce something further. They may give rise to a
succession of similar cells which may float, as blood-discs, in the cir-
culating stream, to be afterwards converted into the different tissues
of the individual ; they may, as in the Aphides, retain suflBcient of
the fecundative and organising forces to disseminate the like virtue
through their multiplied subdivisions, and give rise to the different
tissues and organs of a new individual, which in its turn may include
some unmetamorphosed nucleated cells, with organising energies si-
milar to those of the parent cell of which they were the fissiparous
progeny.

The individual Aphides thus generated are all, until the last
brood, females, which are brought forth as larva, and generate and
perish under that form. The last brood includes both sexes,
which acquire their full development and winged state, and the
females exclude impregnated ova. The gemmiparous procreation
by the larval polype of the Medusa of similar larvae ; the subsequent
acquisition by both of a more concentrated form, generating the
young discoid Medusae by a series of spontaneous divisions ; lastly,
the acquisition of the distinct sexes and the procreation by impreg-
nated ova by the perfect Medusae, are phenomena essentially ana-
logous to those of Aphidian generation.

The larvae brought forth by the apterous and virgin Aphis have
reached a more advanced state of development than the normally
generated larvae of the Coleoptera and Lepidoptera. The compound
eyes are developed on the head, and the antennae have acquired
their mature form and proportions : the six thoracic legs have at-
tained their due length, are divided into the normal number of
joints, and gain the requisite firmness for use almost immediately

* " A dire vrai, je me refuse a emettre une opinion au milieu d'un tel dedale,
et je tiens pour plus philosophique d'avouer son ignorance dans un phenomene ou
la nature nous refuse raeme Tapparence d'une explication. S'il fallait une expli-
cation a toute force, j'admettrais que la generation se fait ici, comme chez quelques
Entozoaires, par individualisation d'un tissu precedemment organise."

INSECTA.

235

after birth. The only change which these fertile female larv» after-
wards undergo is increase of size and development of the repro-
ductive organs. In the last generation, which is the seventh, the
ninth, or the eleventh, according to the species of Aphis, the fer-
tilising influence would seem to have expired, and developmental
force exhausts itself in more frequent and numerous moultings, in
the formation of wings, and in the modification of the female organs
already described. Many males, which, like the females, acquire
wings, form part of the produce of the last brood, which takes place
in Autumn. They rise in the air, frequently migrate in incalculable
numbers, unite, and the females then produce eggs, which are glued
to twigs and leaf-stalks, retain their vitality throughout the winter,
are hatched in the spring, and give birth to the apterous and larvi-
parous females, which continue to produce successive generations of
similar females until the close of summer.

But why, it may be asked, should there be this strange combination
of viviparous generation at one season and of oviparous generation
at another in the same insect? The viviparous or larvi parous gen-
eration effects a multiplication of the plant-lice adequate to keep
pace with the rapid growth and increase of the vegetable kingdom
in the spring and summer. No sooner is the weather mild enough
to effect the hatching of the ovum which may have retained its vi-
tality through the winter, than the larva, without having to wait for
the acquisition of its mature and winged form, as in other insects,
forthwith begins to produce a brood, as hungry and insatiable, and as
fertile as itself. The rate of increase may be conceived by the fol-
lowing calculation : —

The Aphis lanigera produces each year ten viviparous broods, and
one which is oviparous, and each generation averages 100 indi-
viduals.

1st generation 1 aphis produces

2d 100

3d 10,000

4th 1,000,000

5th 100,000,000

6th 10,000,000,000

7th 1,000,000,000,000

8th 100,000,000,000,000

9th 10,000,000,000,000,000

1 0th 1 ,000,000,000,000,000,000

If the oviparous generation be added to this you will have a thirty
times greater result.

hundred,
ten thousand,
one million,
hundred millions,
ten billions,
one trillion,
hundred trillions,
ten quatrillions.
one quintillion.

236 LECTURE XVIII.

The last change in the working of the procreative machinery of the
Aphides is essential to the preservation of the race ; the larvae of
these little delicate insects would be all destroyed by the winter
frosts ; but the cold is effectually resisted by the latent vital forces of
the ova, which are defended by a compact case of mucus, and are
instinctively glued by the parent to the sheltered nook or crevice
of the plant, of the inherent temperature of which they have the
benefit.

Other Hemiptera and all the Orthoptera produce eggs in which
the development of the embryo proceeds in the order already de-
scribed until it attains as advanced a state as that of the viviparous
larva of the Aphis. The subsequent changes of these insects consist
in the growth of all the parts, which takes place chiefly during the
period of the moult and the gradual acquisition of the wings, which
is not attended with any loss of activity or diminution of voracity.

The successive states of an apodal worm, of a worm with feet, and of
one with feet and w4ngs, being accompanied likewise with the ac-
quisition and perfection of the antennal and visual organs of sense,
and of the internal and external organs of generation, and often with
great changes in the digestive, muscular, and nervous systems, in the
development of one and the same insect have been emphatically
termed metamorplioses. Entomologists have defined various kinds of
metamorphoses under special heads, as the coarctate, obtected, in-
complete, semi-complete, and complete metamorphosis.

The progress of the insect through these several stages being in
many species interrupted, and active life enjoyed for a longer or
shorter period under one or other of the immature forms, these have
been sooner and more prominently brought under the notice of the
naturalist, than if they had had to be sought for, as in the bird or
mammal in the early periods of the development of the minute embryo.
They have consequently had assigned to them a character of singu-
larity and exception which they do not intrinsically deserve. The
different stages of development have been likewise, for the most part,
studied only in the instances in which they are manifested by insects
after exclusion from the egg, and thus their minor modifications and
differences have attracted more attention than their essential resem-
blances and relations to one and the same type and course of de-
velopment.

As soon as the young insect breaks through the egg-shell it is
called a Larva, whatever grade of development it may have attained
in ovo. During the period when it acquires the wings it is called a
Pupa.

From the importance which has been assigned in some entomo-

INSECTA. 237

logical classifications to the developmental changes of insects, and
the special denominations that have been multiplied to express them,
you might suppose the " complete," the " semi-complete," the " in-
complete," the " obtected/' and " coarctate " metamorphoses, to be
different degrees and distinct species of transformations. But the
insects which are said to be subject to the semi-complete and incom-
plete metamorphosis pass through the same kind and amount of change
as those characterised by the obtected or coarctate pupa. The dif-
ferences resolve themselves essentially into the place where, and the
time in which, they assume and quit the vermiform state.

The Orthopterous and Hemipterous insects, characterised in ento-
mology by a semi-complete metamorphosis, are, at one stage of their
development apodal and acephalous larvae, like the maggot of the
fly ; but instead of quitting the egg in this stage, they are quickly
transformed into another, in which the head and rudimental thoracic
feet are developed, as in the hexapod larvae of the Carabi and
Petalocera ; the thorax is next defined and the parts of the head ac-
quired, at which stage of development the young Orthopteran cor-
responds with the hexapod antenniferous larva of the Meloe ; but it
differs from both these kinds of Coleopterous larvae in being inactive
and continuing in the egg almost until all the proportions and cha-
racters of the mature insect are acquired, save the wings.

Oddly enough that development is called " a complete metamor-
phosis," which is permanently arrested at the stage in which the or-
thopterous insect enters life, and the only hexapod insects, as the
apterous Cimex and Pediculus in which the metamorphosis is never
completed, are those in which it is said to be " complete." Bur-
meister, however, seems to be the only Entomologist who has pointed
out the inaccuracy of the Fabrician definition;* but he failed to
free himself from the thraldom of words when he supposed that,
in the development of any insect there was, " properly speaking, no
change of form, but merely a repeated casting off of the exterior
skin." f

With regard to the terms incomplete, obtected and coarctate, they
indicate, in fact, comparatively unimportant modifications of the last
moulted skin of the larva of those insects which are torpid or quiescent
at the period of the development of the wings. In the bee and
beetle (^Hymeno'ptera and Coleoptera), the legs, wings, and antennae
bud out and carry with them processes of the last larval integument,
which thus forms in the pupa special sheaths for each growing organ

* Manual of Entomology, by Shuckard, p. 43.
f Ibid. pp. 33. 428.

238 LECTURE XVIII.

of sense or locomotion in the perfect insect, and which organs are
therefore comparatively free, although the pupa be quiescent. La-
raark called such pupae " Mumiae."

In the obtected Lepidoptera the growing wings, antlia, antennee,
and thoracic legs are only partially covered by the pupal integument,
being lodged in recesses on its inner surface, which make correspond-
ing projections on its exterior, where their form and position may
thus be recognised.

In the coarctate metamorphosis of the Diptera, the larva sheds its
last skin before the growing legs and wings have impressed their
forms upon it, and the exuvium constitutes an egg-shaped horny case,
upon which there is not the least indication of the parts of the perfect
insect.

Under whatever form the insect be excluded from the egg^ if we
trace its development further back, we shall find that the tendency of
the mysterious multiplication, arrangement, and transformation of the
hyaline and vitelline particles is vermiform. In all insects the em-
bryo first manifests itself as an apodal smooth Entozoon ; next as an
anellide of thirteen rings : in all insects the first segment is quickly
modified and the mouth established ; and in this state the larva is ex-
cluded in some insects, as the bee and fly, without any appendages
being developed.

The maggots of the order Diptera typify the Entozoa ; they have
no distinct scaly head, and no thoracic legs ; hence they have been
termed " vermilarves." They represent the parasitic worms not only
in structure but in habits ; the larvae of the Gasterophili called "bots,"
pass that stage of their existence in the alimentary canal of higher
animals. The larva of the Anthorugia canimilaris may be in like man-
ner considered as entozoa of the human subject. There is a breeze-
fly (CEstrus homi?iis)* which deposits its egg beneath the integu-
ment of the living body, and its larva there grows and flourishes like
the Filaria in the cellular tissue. The larva of a species of Cuterebra
occasionally finds its way into the human frontal sinus. Other vermi-
larves, as those of the CEstri Bovis and Tarandi^ are developed be-
neath the integument or in the nasal sinuses of the Ruminants
indicated by their specific names. I know not to what other modes
of animal life than that of the parasitic Entozoa we can compare the
habits of the voracious maggots of the flesh-fly, the essential condi-
tion of whose existence is the putrid flesh of higher organised beings.
Here, however, the development of helminthoid larva has been bene-
ficently ordained in order to neutralise the noxious effects of the

* Howship, Proceedings of the Royal Society, March 21, 1833.

INSECTA. 239

otherwise inevitable processes by which dead animal matter reverts
to its primitive elements. Insignificant indeed do these larvae seem
to be in the scale of nature, yet Linnaeus* used no exaggeration when
he averred that three flesh-flies would devour the carcase of a horse
as quickly as would a lion. The assimilative power is so great in the
meat-maggot that it will increase its own weight two hundred times
in twenty-four hours.

But the organising energies are not exhausted by the rapid
growth of the larva ; some remain to be exercised in the formation
of the new and peculiar organs which entirely change the form and
properties of the creature. For this exercise they require the sus-
pension of all the ordinary actions of life. The larval skin is
thrust off by the new integument of the new organs, and is con-
verted into an opaque brown case : the inclosed insect shrinks partly
by the loss of exhaled fluids, partly by the condensation of its former
soft tissues into the new and firm substances constituting the legs
and wings. A large and distinct head is now developed, with eyes,
antennae, and instrumenta cibaria ; all which processes are carried
on in the quiescent concealment of the opaque and dark exuvium,
like the analogous processes in the egg of the Orthopterous, and
within the womb of the pupiparous, insect. The active carnivorous
vermilarve returns, in fact, a second time to the state of an ovum,
when it becomes the coarctate pupe ; and the perfect insect, splitting
its cerement, issues forth as by a second birth.

The larvae of the gnats (Culex) and crane-flies {Tipidce) have a
distinct corneous head with jaws : the former have a plumose anal
coronet, by which they sustain themselves at the surface of the
water : the orifices of the tracheae are placed in the middle of this
coronet. A pair of tracheal tubes extend through the long, slen-
der, and extensile anal canal of the aquatic grub of the Musca
(Bristalis) tenax. By this mechanism, which is analogous to the
tube of the diving bell, the rat-tailed larva can derive its requisite
supply of air from the surface while groping for food in the mud at
the bottom of the pool.

The economy of the Hymenoptera and the various circumstances
attending the development of their apodal larvas form the subjects of
a long chapter in the History of Insects.

I must be governed in the unavoidably brief selection from this
rich storehouse of intereresting facts by the specimens which Hunter
has left for our instruction. Here (exhibiting the preparation No.
3104.) we have a portion of the nest of a social hymenopterous

* Systema Naturae, Musca carnaria.

240 LECTURE XVIIl.

insect of the wasp tribe {Polistes tnajor), showing the larvae and their
cells in every stage of growth : the smallest larvae and the shallowest
cells are at the lower margins of the pendent nest ; and observe how,
in these beginnings of cells, the part of the incomplete circumference
forms two, three or more sides of a complete hexagon, demon-
strating that this is the form of cell originally and expressly made
by the insect, and not the accidental and inevitable result of the
reciprocal pressure of originally cylindrical cells, moulded upon the
bodies of their simultaneously -working fabricators. The parent wasp
of this colony began her labours in spring. A solitary mother and
independent builder of the required shelter for her offspring, she
herself nursed and fed her first brood, which, being non-breeding
labourers, soon aided their parent in building the cells and rearing
her larvae. You will observe that the full-grown grubs are shut in
by a transparent convex pellicle, which covers the mouth of the
cell.

In the common wasp, the larva is hatched eight days after oviposi-
tion ; it grows to its full size in twelve to fourteen days, then spins
its delicate hood, casts its integument, which has grown with its
growth from the time of quitting the e^g, and, after a passive pupa
state of ten days, emerges a perfect insect. The males and perfect
females are reared at the beginning of autumn : the abundance of food
yielded by the ripe fruit at that season may influence the higher de-
velopment of the larvae, which are fed by the regurgitated contents of
the crop of the nursers.

The fertile females share with the non-breeders or neuters of the
rapidly increasing community, the labour of rearing the young broods :
the males, or drones, perform no kind of work. At the close of
autumn, when provender is scanty, and hardly to be got, the neuters,
by a strange, and, as it would seem, perverted instinct, save the later
brood of grubs from the pangs of famine by killing and casting them
out of the nest. The young females are impregnated previous to the
setting in of winter : the males soon after die ; the females then dis-
perse, seeking winter quarters in sheltered situations ; and those
which survive the rigours of the frosty season commence, at the re-
turn of spring, the foundation of a new colony.

The higher instincts of the honey-bee (Apis onellifica) teach it to
lay up a winter store of food, upon which, the males having been
destroyed on the performance of their sole office, the queens, with a
family of neuters, subsist till spring. The neuters alone now re-
commence their labours of housing, in waxen cells, the eggs of the
fertile female, and feeding the larvae. New colonies so raised suc-
cessively emigrate from the parent hive, or swarm ; they consist of a

INSECTA. , 241

queen or fertile female, and perhaps a thousand attendant neuters.
Thus the association, which is annually dissolved and recommenced
by the wasps, is permanent in the honey-bee, and the fertile female,
or queen, never shares with the neuters the labours of the hive.

The development of the bee is m re speedy than that of the wasp ;
the larva is hatched in three days after the exclusion of the egg ; it
feeds and grows five days ; is then shut up by the workers, spins itself
a cocoon in thirty-six hours, remaining a passive pupa eight days ;
then breaks through the lid and emerges in its perfect state. Thus
the whole period of development from the exclusion of the ovum is
twenty days ; this, however, relates to the neuter. The male or drone
larva spends only twenty-four hours in spinning its cocoon, and emerges
on the sixteenth day after its deposition as an egg. A young queen
is perfected on the twenty-fourth day.

In these preparations (Nos. 3117. to 3123. inclusive) are showm the
irregular subelliptical cells with the larvge and perfect insects of the
humble bees (^Bombi terrestris and lapidarius.) The societies of this
genus, which consist of about sixty, and occasionally of two hundred
individuals, continue, as in the wasp-tribe, only until the beginning
of winter, and the few impregnated females which survive the frosts,
found fresh colonies at the commencement of the following spring-
The fertile female shares in the labours of the community which she
has originated, and she is provided, like the neuters, with the dense
fringe of hair surrounding the pollen plate of the hind legs, which the
queen of the hive-bee does not possess. The first progeny of the
humble-bee are neuters ; the males are not developed until autumn,
and they are the produce of a smaller kind of fertile female. The
whole economy of the humble-bee was very completely observed by
Hunter, whose MS. notes on this subject have been published in the
fifth volume of the Physiological Catalogue.

The larvge of the Coleoptera are active, although some, as the nut-
grub, are apodal, like the larvae of the bee. In most of the herbivo-
rous species the thoracic legs are represented by fleshy tubercles ; but
the larvae of the carnivorous beetles have the thoracic legs more com-
pletely developed before quitting the ovum. The head is horny, and
the trophi are well developed in all : the jaws frequently resemble
those of the perfect insect, as in the Carahid<s, the larvae of which
likewise have antennae.

The circumstance of most physiological interest in the development
of the Coleopterous order of insects is the great length of time during
which the species actively exist in the vermiform or larval stage of
their development. The larvae of the cockchafer typify the earth-

R

242 LECTURE XVIII.

worm in their habits, and continue for three years burrowing in the
soil and devouring the roots of grass and other vegetables. The larva
of the stag-beetle bores its way into the trunk of a tree, generally a
willow or oakj and remains there six years. It is furnished with two
powerful jaws, with Avhich it gnaws the wood. It forms a cocoon of
the minute chips or tan, to which it reduces the wood, and passes a
considerable period in the pupa state ; during which, the large horns
of the male are folded upon the breast and abdomen, protecting the
antennae and legs.

The anatomy of an insect in its different stages of development, and
the changes of both the external and internal parts in the progress
from the larva to the imago state, have been most accurately
and closely examined in Lepidopterous insects. Many of these
changes are shown by Hunter, in his extensive series of prepara-
tions of the silkworm moth.* They were investigated by Lyonnet
in the Cossus ligniperda. They have been described and illustrated
with much accuracy and detail by Herold in the Papilio Brassicce,
and by Mr. Newport in the Sphinx Ligustri. The larvae of the Le-
pidoptera quit the ^^^ with a scaly head and jaws, with three pairs
of thoracic legs, short, and with claws (^fig. 104, o,p,q), and usually

104

Sphinx Ligustri. Larva.

four pairs of tubercular prolegs (r, r), supported by the sixth, seventh,
eighth, and ninth segments ; sometimes there is also a fifth pair
upon the anal segment. The prolegs, which entirely disappear in the
pupa, are however less constant than the thoracic legs. The larvae
of the lepidoptera are commonly herbivorous, and devour considerable
quantities of vegetable matter. The coarsely masticated leaves are
conveyed by a short and wide oesophagus {Jig. 104. c?), to a much
longer and wider chylific stomach (k). Six pairs of capillary bile-
tubes (/) indicate by their insertion the commencement of the intestine
(m), which terminates by a wide, short, and longitudinally plicated
rectum at n, upon the last segment.

In its perfect state, the butterfly, or sphinx, subsists only on
the fluids of vegetables : its maxillary apparatus is converted by the
abrogation of the horny mandibles and the extreme prolongation of
the maxillae, into the antlia {fig. 105. ^), already described. A

* See Nos. 2976. to 3036. inclusive.

INSECTA.

243

long and slender oesophagus, y, conveys the fluids to the chylific
stomach, and to a v/ide crop {fig. 105. k\ which during the pupa
J05 state has been gradually

expanded from one side
of the end of the gullet.
The chylific stomach (g)
has shrunk into a compa-
ratively short fusiform
cavity, which is still cha-
Sphinx Ligustri. Imago. racterised by the trans-

verse sacculi and constrictions. The small intestine (/) has dimi-
nished in width, but increased in length, and now lies in several con-
volutions between the chylific stomach and colon, the upper part
of which has also been produced into a cascum (m). The biliary ves-
sels are diminished in length, but still communicate, by a short com-
mon duct on each side, with the commencement of the small intestine.

In the bee the metamorphosis of the digestive organs is still more
striking than in the butterfly, inasmuch as the alimentary cavity con-
sists, beyond the short and wide oesophagus, exclusively of a large
transversely plicated chylific stomach without intestine or vent.

The larvae of bees and wasps have from four to six biliary vessels,
which shrink in diameter and contract in ength during the pupa state.

The gizzard is never present in the vermiform larvae of the Coleop-
tera, although usually possessed by the perfect insect.

In the larvae of the Scarahm^ Melolontha, and most herbivorous
Coleoptera, the chylific stomach is shorter than in the imago ; but it is
furnished at both ends with caecal appendages, which disappear during
the metamorphosis, except in the genus Hister^ in which some traces
remain in the perfect insect.

The salivary vessels of the caterpillars of the Lepidoptera are of two
kinds ; one pair is short and broad, sometimes vesicular, as in the
Cossus ligniperda, and their ducts terminate at the base of the max-
illae. Those of the second pair are very long and slender, occupying,
with their longitudinal coils, the sides of the abdomen, and sending
their slender ducts forwards to unite together and terminate upon a
peculiar prominence upon the under lip, which is called the spinneret.*
These tubular glands, though classed with the salivary apparatus, are
peculiar, in their full development, to the larvae, and are called " se-
ricteria " or silk-tubes, because they prepare the glutinous material,
or silk, which the larva spins to form its cocoon. In the perfect in-

See preps. Nos. 2985. to 2988.
R 2

244 LECTURE XVIII.

sect, the remains of the salivary apparatus are limited to the thorax,
and the common duet opens beneath the tongue.

The epithelial lining of the alimentary canal of the larva is shed at
each moult ; that of the closed stomach in the bee-maggot is evacu-
ated in the pupa state through the new formed anus.

The superabundant nutriment prepared by the voracious larva is
stored up in the condition of masses of fat which surround the viscera
and occupy their interspaces.

The parasitic Ichneumons introduce their ova beneath the skin of the
larvae of Lepidoptera. When hatched the Ichneumon larvae subsist
upon the fat of the caterpillars, which they infest. They avoid pene-
trating the alimentary canal, but evidently destroy many of the minute
branches of the trachea which ramify in the adipose tissue. Such
wounded tracheae probably permit the escape of sufficient air for the
respiration of the parasitic larvae ; for though the caterpillars so in-
fested survive and go into the pupa state, they are uneasy, and evi-
dently diseased ; the loss of the adipose store of nutriment prevents
the completion of the metamorphosis, and instead of a butterfly, a
swarm of small Ichneumons emerges from the cocoon.

With respect to the outward form and integuments of the ver-
miform larva, these are contracted lengthwise, and partially dilated
during the pupa state. The longitudinal muscles contract, and are
permanently shortened by interstitial absorption : they shorten the
body by sheathing the segments one within the other, the intus-
suscepted portions being afterwards modified or removed.

The dorsal vessel {fig. 104-, s), which is developed above the
intestine, and begins to pulsate before the larva quits the ^g^^., un-
dergoes a corresponding change with the common integument in the
pupa state. It seems to be contracted by a series of intus-susceptions ;
the abdominal part is slightly expanded, more definitely divided into
chambers, and better provided with valves: the thoracic portion is
simplified, shrunk in diameter, and is more distinctly defined as an
aorta sent off from the heart, {fig. 105.)

The respiratory system undergoes still more remarkable modifi-
cations. The branchiae of the aquatic larvae either disappear or are
developed into wings : the long pneumatic tubes of those which,
living in water, breath air, shrink and disappear. The partial dilat-
ations of certain tracheae to form reservoirs of air for diminishing the
specific gravity of the body, begin to be formed in the pupa state of
the flying insect.

Herold has shown that germs of the generative organs exist in the
larvae of the Lepidoptera : the testes appear on each side as four
nucleated cells in a longitudinal series, which, by progressive coa-

INSECTA. 245

lescence longitudinally, and by approximating transversely, and ulti-
mately uniting at the middle line, first form an eight-chambered, and
afterwards a spherical, gland, (^fig^ 105. s.) The ovaria, retaining
their primitive separate state, increase in length, and assume the spiral
disposition in the pupa state.

I have already* described the chief changes which the nervous
system undergoes during the transformation of the larva into the
imago, and need only now observe that the general principle of those
changes is like that which governs the modifications of the muscular
system, viz. a localisation of special masses at particular parts for
special purposes, the result of which is the dejDarture from a common
to a particular type of arrangement.

One of the most obvious and remarkable phenomena in the larval
life of an insect is the successive sheddings of the skin. The number
and frequency of the ecdyses varies in different species, and relates to
two circumstances, viz. the rapidity of the growth of the body, and
the susceptibility or otherwise of the skin to be distended or to grow
with the increase of the body.

The soft-skinned maggots of many flies, which acquire a vast
increase of size during their brief larval state, never moult until they
change into pupae, when the exuvium forms the pupa-case. In like
manner the soft-skinned apodal larvae of the Hymenoptera do not
moult until they have acquired their full size. The caterpillars of
the Lepidoptera moult at least three times, and some more frequently ;
the Bombyx villica, for example, from five to eight times, and the
tiger-moth (Arctia caja) ten times.

With regard to the nature of the mutations and ecdyses which
culminate in the perfect insect, I should hardly have felt justified,
after what has been already detailed respecting the development of
the larva in the egg, in referring to the hypothesis of Swammerdam,
— that the imago was actually included in the larva, and that all new
skins pre-existed beneath the old one, — if such opinion had not been
adopted to explain the metamorphoses of insects in the admirable
work of our countrymen, Kirby and Spence.* The accurate observ-
ations of Herold on the changes and development of the organs
during the pupa state show these to be, like the original processes of
the development of the larva itself, the results of a transmutation,
increase, and coalescence of primitive elements of the different tissues.

The few instances of the reproduction of mutilated parts in in-
sects have been observed to take place only at the period of the moult,
and are never manifested by the imago. A young Blatta^ in which

* p. 209. t Introduction to Entomology, vol. ii,, p. 61.

R 3

246 LECTURE XVIII.

both the antennae had been cut off, moulted a fortnight after the
operation, and then acquired two new but shorter antennae : the
legs and prolegs of caterpillars are said to be reproduced in like
manner after one or two moultings.

The passive and, as it were, embryonic condition to which most
insects (Coleoptera, Lepidoptera, Hymenoptera, Diptera, many Neu-
roptera) return when, after an active larval life, the organising energies
again superinduce the processes of development upon those of mere
growth, is called the pupa state. The chief modifications of the pupa
have already been explained in relation to the terms coarctate,
obtected, incomplete, by which they were designated by Linnaeus.

Some pupae are protected only by the exuvial skin of the preceding
stage, and have been termed " naked ; " others repose in cases or
" cocoons," artificially prepared by the larva. The valuable silken
cocoons of the larva of the Bombus mori, called, par excellence, the
" silkworm," are familiar examples of pupal chambers. In this
cocoon * of a larger Lepidopterous insect ( Oiketicus Kirbyi), the
larva, by one of those marvellous prescient instincts which give so
much interest to entomological enquiries, covers the close and thick
web of fine and soft silk which it has prepared for its pupal repose
with a strong outer defence of portions of twigs irregularly bound
together by silken filaments : thus suspended to a branch of the tree,
it deceives and escapes the attacks of predatory insectivorous birds.
The pupae whose cocoon remains partially open, as in Saturnia and
Phrygaiiea, are usually called " guarded " {pupce custodiat^).

All pupae which are placed in dark situations are colourless, or
of a yellowish white, and become darker when exposed to the light.
The pupae of most butterflies, which are suspended in open day,
are of a green or yellowish brown colour : some are speckled wath
glittering spots of golden hue, either natural or produced by the
attacks of parasitic insects ; and such pupae have obtained the name
of " chrysalis " and " aurelia."

The active pupae of Orthoptera and Hemiptera are called
" nymphs." These insects, which are also said to have semicomplete
pupae, and to undergo an imperfect metamorphosis, are subjected,
as I trust I have already proved, to the same law of repetition or
analogy which is expressed so conspicuously in insects to which alone
a perfect metamorphosis has usually been attributed : for, although
moulting be no metamorphosis, even when accompanied, as it usually
is in insects, with a certain change in the form of the body, yet the
course of the development of those insects which, after exclusion

* No. 3073.

INSECTA. 247

from the egg, are subject only to ecdysis and growth of wings during
an active nymph-hood, manifests, prior to exclusion, the same ana-
logies, which Oken expresses in the following words : — " Every fly
creeps as a worm out of the egg ; then, by changing into the pupa, it
becomes a crab, and, lastly, a perfect fly."*

It is not, indeed, true that every flying insect creeps, as a worm,
out of the egg : all the Orthoptera and Hemiptera are excluded
under the type of the crab, i. e. with perfectly developed jointed legs,
eyes, antennae, and maxillary organs. The metamorphoses which the
locust undergoes in its progress from the potential germ to the actual
winged and procreative imago are nevertheless as numerous and
extreme as those of the butterfly. The differences are relative, not
essential ; they relate to the place in and the time during which the
metamorphoses occur, and to the powers associated with particular
transitory forms of the insect. The legs of the worm-like embryo-
locust were once unarticulated buds, like the prolegs of the cater-
pillar ; but the creature was passive, and development is not superseded
for a moment by mere growth ; these organizing processes go on si-
multaneously, or, rather, change of form is more conspicuous than
increase of bulk: the six rudimental feet are put to no use, but
constitute mere stages in the rapid formation of the normal seg-
ments, whicli attain their mature proportions and their armature of
claws and spines, before the egg is left. The first segment of the
originally apodal and acephalous larva is as rapidly and uninter-
ruptedly metamorphosed into the mandibulate and antennate head,
with large compound eyes.

Thus developed, the young Orthopteran or Hemipteran issues forth
into active life. It may at once begin the great business of its ex-
istence, the propagation of its kind, as in the Aphis, and feed and die
without further change of form ; but generally the active crab-like
larvae are subject to three moults. After the first the larva has merely
increased in size ; but the rudiments of the wings begin to bud forth
beneath the second skin, and, after the second ecdysis, they present
themselves externally as small leaves, which cover the sides of the
first abdominal segment. When this active pupa or nymph again
moults, the insect attains its perfect condition ; the, at first, short,
soft, and thick wings rapidly expand to their full size, then dry in
the air, the circulation of the blood along the nervures is arrested,
and the metamorphosis of the individual is complete. Here, then,
we see that the pupa stage, which, in the butterfly, was passive and
embryonic, in the locust is active and voracious, whilst their re-
spective conditions in the larval state are reversed : the whole period

* Naturgeschichte fiir Schulen, p. 577.
R 4

248 LECTURE XVIII.

of the life of the Orthopterous insect, from exclusion to flight, may,
if its organisation during that period be contrasted with that of the
Lepidopterous or Coleopterous insects, be called an active nymph-
hood.

Entomologists, overlooking that stage of the orthopterous and
hemipterous insects in which they are masked by the vermiform or
true larval condition, have arbitrarily applied the term " larva " to
the more advanced stage in which these insects, with certain Neu-
roptera, quit the egg. Mr. Westwood, seeing that at this stage they
are nearly similar in form to the perfect insect, though wingless, has
proposed to call them " homomorphous," or "monomorphous;" and
those insects in which the larva is generally wormlike, &c. " hetero-
morphous." It needs only an acquaintance with the embryonic
changes of a cockroach or cricket to feel how inapplicable is the term
monomorphous or uniform to such an insect or its development.

In the Coleoptera and Lepidoptera the general articulate type is
longer retained, and the particular one later acquired : in the He-
miptera and Orthoptera, the morphological and histological changes
more rapidly and uninterruptedly effect the ascent from the common
to the special form. The insects with a so called imperfect metamor-
phosis, contrary to the statement of Burmeister*, do pass through the
earlier forms of the articulate subkingdom, but more rapidly and
uninterruptedly than those in which the metamorphosis has been
deemed more complete. In these the worm-like insect or larva is
active, and the crab-like insect or pupa passive ; in those the larva is
passive and the pupa active.

If the different stages in the development of man were not hidden
in the dark recesses of the womb, but were manifested, as in insects,
by premature birth and the enjoyment of active life, with a limita-
tion of the developmental force to mere growth ; if the progress of
development was thus interrupted and completed at brief and remote
periods, with great rapidity, and during a partial suspension of active
life ; — his metamorphoses would be scarcely less striking and extreme,
as they are not less real, than those of the butterfly.

As the insect must pass through the earlier forms of the Articulate,

* Burmeister's statement is, " In insects with an imperfect metamorphosis there
cannot consequently " (the consequence is a hypothetical necessity in Nature, for a
difference among insects with respect to their metamorphosis) " be a passage through
the earlier forms and grades of the animal kingdom." (Shuckard's Translation,
p. 423. ) But no insect ever passes through the forms and grades of the radiate
subkingdom. Commencing as a Hydatid, it quits that subkingdom by the analogy
of the Entozoa, and its subsequent grades are through the forms of the Articulata
exclusively. No insect ever is or resembles the ciliated Infusory, the Polype, or the
Acalephe.

INSECTA. 249

so must man through those of the Vertebrate, subkingdom. The
human embryo is first apodal and vermiform : not, however, at any
period an articulated worm. The metamorphoses of the germ-cells in
the spherical (hydatid-like) ovum have laid down the foundation of
the nervous sj^stem coeval with the first assumption of a definite
animal form ; and, by placing it along the back as a rudimental spinal
chord, have stamped the vermiform human embryo with the charac-
ters of the apodal fish. When the four undivided compressed extremi-
ties bud out, the form of the abdominal-finned fish, or of the Enaliosaur,
is indicated. The development of the heart, of the vascular arches,
of the generative organs with their cloacal communication with the
rectum, typify the oviparous reptile. But these stages are rapidly
passed, and the special character acquired.

Let us suppose that man, or any mammiferous animal, quitted the
ovum and the parent in the guise of the fish, passed a certain period
in water, retaining the branchial structure, the undivided extremities
and the cloaca, and acquired only increase of bulk under that
guise ; let us suppose that then such larva, seeking some safe hiding
place, returned to embryonic passivity and unconsciousness, and was
rapidly transformed into the perfect state. Under this hypothetical
modification of the course of human development, the changes of
form would be plainly recognisable, and in the accessory circum-
stances, as well as the essentials,, the mammalian metamorphoses
would resemble those of the insect.

If, on the other hand, every insect had been developed like the
Diptera pupipara^ and the changes from egg to larva and from larva to
pupa had been hidden in the oviduct of the mother, a long period might
have elapsed before the recognition of these metamorphoses, and they
could only at length have been discovered by a series of embryo-
tomies, like those that have brought to light the corresponding
metamorphoses of man and the mammalia generally.

By a premature exclusion and activity of the embryo, and by
alternate periods of growth and development, one small group of
vertebrate animals, the anourous Batrachia, do actually manifest the
correspondence with the metamorphoses of insects, which I have
illustrated by an instance of hypothetical possibility in man. Nay,
do not the Marsupial mammalia offer an example of the premature
exclusion ? It needed only that the young kangaroo, with its equal
and rudimental limbs, should possess, like the tadpole or caterpillar,
the power of self-subsistence, and have gone on feeding and growing,
whilst the further and final changes of form were reserved for, and
concentrated in, a future brief period, to render the parallel almost
complete. The creeping or swimming larva of the Mammal M'ould

250 LECTURE XIX.

then have, gained its instruments for leaping, as the caterpillar ac-
quires its organs of flight, and the concomitant development and
metamorphoses of the organs of sense, of digestion, and of generation
would have been closely analogous in both animals.

LECTURE XIX.

ARACHNIDA.

There remains one class of articulate animals to be considered in
our present ascending survey of the animal kingdom, and which,
therefore, you will conclude to be the highest organised of the
homogangliate Invertebrata. Yet the species which are grouped
together under the name Arachnida never acquire wings ; many are
parasitic, many terrestrial, and a few are aquatic ; there are some,
however, that, notwithstanding their apterous condition, can rise and
float through the air, which they effect in a manner analogous to our
balloon aeronauts, by manufacturing and suspending themselves to a
foreign substance light enough to be buoyed up and wafted along the
atmospheric currents. The animals to which I allude, and whose
anatomy and physiology I propose to make the subject of the present
lecture, are those commonly known under the name of mites, scor-
pions, and spiders.

You will be disposed to ask why these Articulata are held superior
to insects ? They present a more concentrated form of the nervous
system and of the heart: the larger species, likewise, present a
higher condition of the respiratory system, which is less diff'used
than in insects, and in some consists only of air-sacs or lungs. Per-
haps the most essential mark of the superiority of the Arachnida
is the course of their development. The spider undergoes n.o me-
tamorphoses comparable with those of insects. It is at no period of
its development an apodal worm. The mature form is sketched out
from the beginning, the divisions of the body characteristic of the
perfect animal are established before the vitelline mass is included by
the tegument ; and, long before the characteristic palpi and legs are
completed, the equally characteristic ocelli are developed upon the
head. If you should still be disposed to think that the superior
organs of vision and the wings of insects are essential signs of a
higher organisation, by parity of reasoning, you must be prepared to
place birds above mammals.

ARACHNIDA.

251

The Arachnida, like insects, are organised to live in air ; but they
are distinguished at first sight by the general form of the body and
the number of their legs, and by some important modifications of
their internal structure. The head is always, in the Arachnida, con-
founded with the thorax, and is deprived of antennae, or at least of
homologous parts exclusively employed in sensation. They have
four pairs of legs. Some of the species respire by pulmonary sacs
only, in others these are associated with ramified tracheee, and the
smaller Arachnidans breathe, like insects, by tracheae exclusively. The
dorsal vessel and a circulating system exist in all : the heart presents
a more compact and muscular form in the pulmonary Arachnidans.

The integument is chitinous, as in insects, but presents the same
variations in density, in difl?"erent species, as in the winged Articulata.
In the scorpions it is as dense and inextensible as in the Coleoptera :
in the spiders and mites it is generally softer than in insects, espe-
cially that of the abdomen.

The body is divided into two principal parts, of which the anterior
is called the " cephalothorax," because it answers to the two first
segments of insects in a confluent state : the second and larger
division is called the abdomen ; it is generally larger and wider than
the first, from which it is divided by a deep constriction ; but in
scorpions it forms, as in Crustaceans, a slender continuation of the
thorax, a kind of caudal appendage divided into many joints. The
organs of locomotion are all attached to the cephalothorax, and
consist of eight legs, presenting different grades of development in the
different forms of the class, but, in most, being very similar to those
of insects, and almost always terminated by two hooks.

The microscopic parasite of the sebaceous sacs and hair-follicles of
the human skin, lately discovered by Dr. Simon of Ber-
lin, and described in Miiller's Archiv. fUr Physiologic
(1842, p. 218. pl.xi.), represents the lowest organised
form of the class Arachnida^ and, like the parasitic
Cymothoe and Bopyrus of the Crustaceous class,
makes a transition from the Anellides to the higher
Articulata. In length, it ranges from ^^th to -j^Qih.
of an inch. Fig. 106. gives a magnified view of the
human hair-follicle (a), containing the bulb of the
hair (6), the appended sebaceous sac (c), and the
duct {d) containing the parasitic Arachnidan in ques-
tion (e). That this parasite ranks with the Arach-
nida, and not with the red-blooded or any of the lower
organised worms, is evident from the division of the
body into thorax and abdomen, from the structure of

Demodex fol-
liculorum in situ.

252

LECTURE XIX.

the head and mouth, which are confluent with the thorax, and from
tiie undivided abdomen. The thoracic appendages {fig. 107. c, c),
107 i eight in number, as in the Arachnida, are however of

"W^ ^^^ simplest and most rudimental kind, and are terminated
by three short setae ; the Anellidous type of the locomotive
appendages being still retained. The integument of the
abdomen is very minutely annulated. The mouth is a
suctorial one, or proboscidiform, consisting of two small
spine-shaped maxillae (b), and an extensile labium, capable
of being elongated and retracted ; it is provided on each
side with a short and thick maxillary palp (a, a), consisting
of two joints, and with a narrow triangular labrum above.
Although the structure of the mouth, as described and
figured by Dr. Simon, has much analogy with that of the
Acari, like which, also, the follicular parasite in one of
its stages of development is a hexapod, yet it differs
Demodex foi- from the Acctri, and from all other Holeterce of Dusres, in

liculorum,

magnified. the articulations of the thorax ; whilst it equally differs
from the Pseudo-scorpionidce^ and the PycnogoiiidcB, which have the
thorax articulated, in the rudimental form of the feet, and the struc-
ture of the trophi.

It can hardly be supposed that the changes of form indicated by
the figures 8, 1, and 2 of Dr. Simon's memoir can be acquired without
ecdysis ; but such a metamorphosis, with the natural divisions of the
body and the structure of the oral and thoracic appendages, indu-
bitably raise the parasite of the hair-follicle above the Entozoa_, to
which class Prof. Erichson, in Dr. Simon's memoir, has correctly
stated that the present parasite cannot belong. For the reasons
above given, I cannot assent to the place which that accomplished
naturalist has assigned to the Arachnidan in question among the
AcaridcB, much less to the genus Acarus. Of the generic distinction
of the parasite there can be no doubt, and I therefore propose to call
it Demodex folliculorum, from ci]uoq, lard, and cijt,, the name of a
boring worm, indicative of the habitat and vermiform figure of
this parasitic arachnidan, which insinuates itself into the hair-follicles
and the sebaceous glands that communicate therewith.

In some of the small and parasitic tracheary Arachnida, or mites,
certain pairs of legs are terminated by adhesive suckers, and others
are occasionally terminated by setae, as in the itch-mite (Sa?'coptes
Galei, fig. 108.).

The mouth, in all Arachnidans, is situated on the anterior segment
and is provided with instruments adapted either for suction or mas-
tication. In the parasitic mites the rudiments of the jaws are more

ARACHNIDA.

253

Sarcoptes Galei, or itch-
insect, magnified.

or less enveloped in a sheath formed by the lower lip : the maxillary-
palpi are usually the only parts which have
free and independent movements, and their ex-
tremity is commonly armed either with a hook
or with a pair of small nippers.

In spiders the mandibles (^fig. IM. ci) are
situated at the front of the head and are
terminated by a moveable and very sharp hook,
which is pierced at its extremity by a small
fissure, serving to give issue to the poison se-
creted by a gland lodged in the preceding
joint. The maxillae {fig, 114. h, h) are two in
number, and the labium {fig. 114. c) situated
between these organs is composed of a single
piece. The maxillary palpi {fig. 114. c), com-
pared with those of insects, are of great length
and size, and resemble the thoracic feet, which, in the Mygale, they
nearly equal in length. In female spiders they are terminated by a
single moveable claw: in the males the last joint {fig. 114. c?) is
dilated, and presents a more complicated structure. In the scorpion
the mandibles are short and terminate in a pair of strong pincers : the
maxillary palpi are proportionally more developed than in the spiders,
and, like the mandibles, they terminate by pincers, which are so
strong and large in the great scorpion {Buthus Africanus), as to
resemble the chelae of the Crustacea, and more especially as they
are succeeded by four pairs of simple and smaller thoracic legs.

In the genus Galeodes the mandibles are chelate, but much longer
and larger than in the scorpions. The maxillary palpi resemble small
slender feet, but without the terminal hooks ; and the succeeding pair
of legs being similarly modified, only six ambulatory feet of the
ordinary structure remain. Two rudiments of antennae have been
noticed attached to the mandibles in certain species of this genus.
The head is likewise more distinct from the thorax, and it supports
the first of the four pairs of legs usually ascribed to the Arach-
nidae. These modifications, with the union of the ocelli into two
groups, indicate the Galeodes to form the passage to the Hexapod
insects.

The modification and the connections of the pair of legs which
succeeds the maxillary palpi in the Galeodes, demonstrate that they
are the analogues of the labial palpi in Hexapod insects. The position
of the rudimental antennae in the same interesting genus confirms the
indication afforded by the nervous system in spiders and scorpions,
that the antennae are confluent with the mandibles, if these be not

254 LECTURE XIX.

altogether modified antennae, as Latreille supposed to be the case in
the present class.

In the composition of the cephalothorax of spiders^ M. Audouin
has discovered that the tergal elements of the coalesced segments are
wanting, and that the back of the thorax is protected by the elon-
gation, convergence, and central confluence of the epimeral pieces ;
the sternal elements have coalesced into the broad plate (^fig, 114. A),
in the centre of the origins of the ambulatory legs, from which it is
separated by the episternal elements. The traces of the original se-
paration of the four epimeral pieces may be easily distinguished in
some spiders, as the Pholcus rivulatus. The non-development of
the tergal elements explains the absence of wings, which we have
seen, in the Articulata, to be the appendages of those elements, and to
be very frequently restricted to the branchial function. The tergal
parts of the thoracic segments are equally absent in the decapod
Crustacea ; but the back of that division of the body is protected by
the carapace, continued backwards from certain cephalic segments :
when this is raised, the epimeral pieces are seen converging, as in
spiders, but not meeting and coalescing.

The soft and flexible integument of the abdomen in mites and
spiders gives no indication of the segments or their component parts,
but it is favourable for the study of its intimate organisation.
Beneath the epiderm and pigmental layer may be distinguished a thin
muscular chorion, the fibres of which surround the abdomen in
various directions. To the epiderm belong the hairy and spinous
appendages : the large bird-spiders (jMygale) are clothed with a thick
coat of hair : some of the smaller species, as the Aranea domestical
have complex hairs, like the down of birds, implanted by a stem. In
other spiders similarly implanted stems support scales, analogous to
those of the Lepidoptera ; the bright colours of the Salticce and Oxy-
opes are due to these scales.

The muscular system is principally aggregated in the cephalo-
thorax for working the organs of mastication and locomotion ;
there are, however, special muscles in the slender jointed abdomen of
the scorpions for its inflection and extension, and more especially for
the purpose of wielding the poisonous weapon with which it is ter-
minated.

The principal masses or ganglions of the nervous system are con-
centrated around the oesophagus in the cephalothorax of the scor-
pion. From the small supra-oesophageal or cephalic bilobed mass are
sent upwards the optic filaments, forwards the nerves of the forcipated
mandibles or " chelicera," and, backwards, the stomato-gastric
nerves ; the sub-oesophageal ganglionic columns distribute nerves to

ARACHNIDA.

255

the great maxillary cheliform palpi, and to the four pairs of thoracic
legs: two slender continuations of the median columns are continued
along the jointed abdomen or tail, and seven small ganglions are de-
veloped upon them, from which and from the interganglionic chords
nervous filaments are distributed to the surrounding parts.

The ventral continuation of the anterior aorta, which lies loosely
upon the dorsal aspect of the ganglionic chords, must be injected in
order that its branches, which accompany the nervous filaments, may
be distinguished from them. The vessel itself has been mistaken for
a nerve, and has been regarded by some as the motor, by others as the
respiratory tract.

In spiders the central masses of the nervous system are wholly, or
in great part, concentrated in the cephalothorax. The brain (^fig. 109.
and 1 10. c) is a bilobed ganglion sending forwards and upwards the op-
tic nerves (o) from its anterior angles, and below these, the two large
nerves (jti) to the mandibles : a short and thick collar encloses the
narrow gullet, and expands into a second very considerable stellate or
radiated ganglion (5), situated below the stomach upon the plastron : it
sends off five principal nerves on each side ; the first (/?) to the
pediform maxillary palpi ; the second (/) to the more pediform labial
palpi, which are usually longer than the rest of the legs and used by
many spiders rather as instruments of exploration than of locomotion :
the three posterior nerves supply the remaining legs, which answer
to the thoracic legs of Hexapod insects. The nervous axis is
prolonged beyond this great ganglion, as two distinct chords, into the
beginning of the abdomen, where, in the Epeira diadema, it divides

into a kind of cauda
equina; but in the My-
gale a third ganglion
of very small size is
formed, from which
the nerves diverge
to supply the tegu-
ments of the abdo-
men and its contents.

Nervous system, Mygale. The Origin of the

mandibular nerves close to the optic ones from the supra-oesophageal
ganglion strongly indicates the antennal relations of the mandibles,
whilst the analogues of the maxillary and labial palpi receive, as in
insects, their nerves from the sub-cesophageal mass. The stomato-
gastric nerves are sent off from the posterior and lateral parts of the
brain and form on each side a reticulate ganglion, which distributes
filaments to the stomach.

109

256 LECTURE XIX.

Many of the lower parasitic species of arachnidans are blind :
not any of this class have compound eyes, although the stemmata
in some, as the Galeodes and the genus Pliolcus, have their ocelli
arranged in two lateral groups. The scorpions have eight ocelli, two
of which are situated near the middle line, and three on each side,
near the anterior angles of the cephalothorax.

In the spiders the ocelli are generally arranged in a group, upon an
eminence at the middle of the anterior part of the cephalothorax ;
they are generally eight, never less than six in number. The posi-
tion of the four median ones is the most constant ; they generally
indicate a square or a trapezium, and may be compared with the
median ocelli in hexapod insects. The two, or the two pairs of
lateral ocelli may be compared with the compound eyes of insects ;
the anterior of these has usually a downward aspect, whilst the pos-
terior looks backwards ; the variety in the arrangement of the ocelli
of spiders always bears a constant relation to the general conformation
and habits of the species. Dujes has observed, that those spiders
which hide in tubes, or lurk in obscure retreats, either under-ground
or in the holes and fissures of walls and rocks, from which they only
emerge to seize a passing prey, have their eyes aggregated in a close
group in the middle of the forehead, as in the bird-spider {Jig. 109.),
the clothos, &c. The spiders w^hich inhabit short tabes, terminated
by a large web exposed to the open air, have the eyes separated, and
more spread upon the front of the cephalothorax.

Those spiders which rest in the centre of a free web, and along
which they frequently traverse, have the eyes supported on slight
prominences which permit a greater divergence of their axes; this
structure is well marked in the genus Thomisa, the species of which
lie in ambuscade in flowers. Lastly, the spiders called Errantes, or
wanderers, have their eyes still more scattered, the lateral ones being
placed at the margins of the cephalothorax. The structure of these
simple eyes resembles that which has been so well described by
Miiller in the scorpion ; Lyonnet had recognised the crystalline lens.
The iris, or process of pigment which advances in front of the lens, is
green, red, or brown in the diurnal spiders, and black at the back
part of the eye. The nocturnal species, as Mygale and Tarantula^
have a brilliant tapetum, but no dark pigment.

In the scorpion the transparent prominence which indicates each
ocellus is a thick dermal cornea, not divided into facets ; it is deeply
excavated at the middle of its inner surface for the lodgment of the
spherical lens : the back part of this body rests upon, without sinking
into, the anterior surface of a hemispherical vitreous body. The
interspace between this body and the lens forms a circular channel

ARACHNIDA. 257

tilled with aqueous humour "and receiving a circular process of the
thick pigmental chorion which defines the pupil and confines the lens
to the anterior chamber. The pigment coats the retina^ and covers
part of the optic nerve.

Spiders have the sense of hearing, but neither the organ nor its
situation are known. The same may be said of the sense of smell.
The membrane lining the mouth and pharynx may have the faculty
of taste, and influence the Arachnidans in their choice of food. The
soft and often hairy integument must be to a certain degree sensitive,
but touch would appear to be exercised principally by the leg-like
instruments into which the maxillary and labial palpi are converted.

The alimentary canal is short and straight in most Arachnidans : a
slight convolution of the intestine takes place in some spiders : that
of mites is straight and wide, but the stomach, in some, is produced
into lateral sacculi. In scorpions, the alimentary canal extends,
without any gastric dilatation or intestinal convolution, from the
mouth to the anus. Five short and straight diverticula are sent off
at equal distances from each side of the thoracic portion, and are
lost in the granular and seemingly adipose masses, which have been
regarded as a kind of epiploon by some, by others as an hepatic
organ. Two delicate capillary secreting tubes unite on each side,
close to the intestine, and open into that part of the canal which is in
the anterior part of the tail-like abdomen.

The spiders are remarkable for the minuteness of the pharynx and
oesophageal canal. Savigny believed that in some species there existed
three pharyngeal apertures, through which the juices, expressed from
the captured insect by the action of the maxillary plates (^Jig. 109. n)
were filtered, as it were, into the narrow oesophagus. In the Mygale,
however, there is certainly but one aperture : this is defended above
by a horny plate, or rudimental labrum ; below by the labium, which
is soldered to the plastron in the Mygale, but jointed and movable
in most of the smaller spiders.

The pharyngeal fissure (^^. 109. 6) ascends between an anterior con-
vex plate or palate and a posterior concave plate, both which are shed
and renewed at each moult. The slender oesophagus passes back-
wards at a right angle to the pharynx, perforates the nervous ring,
and expands into the stomach {^fig. 109. d). In the house-spider
( Tegenaria domesticd)^ the gastric cavity is produced into four sacs,
which are susceptible of great distension when a large prey is cap-
tured. In another species of spider, the oesophagus {fig. 110. a),
having passed under the brain (c), suddenly expands into a stomach,
almost as broad as the sternum, which sends off a long clavate csecal

258

LECTURE XIX.

110 ,,,,^ ;-, process into the base of the maxillary palpi (e),

and of each thoracic leg (e'). A shorter diver-
ticulum (d) is continued from the upper part of
the stomach. The intestine is contracted where
it passes through the pedicle of the abdomen ; it
slightly expands in its straight course (/) along
the anterior part of that cavity, then contracts
and forms two short convolutions (g), and com-
municates w4th a large globular caecum (A), from
which the short rectum passes to the vent. Four
biliary ducts (i, i) open into each side of the
straight portion of the intestine. Two longer
and more slender urinary tubes (k, k) communi-
cate with the beginning of the caecum, which
seems to stand to them in the relation of an
imen ary cana , pi er. y,,jjjg^j.y bladder. Large masscs of adipose epi-
ploon occupy, in well-fed spiders, the sides of the abdomen, and cover
and conceal the granular csecal terminations of the hepatic organ.

The chyle is received immediately by the veins, and conveyed to
the dorsal vasiform heart. This organ is confined to the six dilated
anterior segments of the abdomen in the scorpions, where it is of
uniform diameter, except at its two extre-
mities : it receives the venous blood from the
surrounding pericardial sinus by ten or eleven
pairs of apertures, each guarded by a pair
of valves. From the anterior and larger
extremity the anterior aorta is continued,
which is short, and soon divides into three
branches : a longer and more slender vessel
is continued along narrow terminal segments
of the abdomen from the attenuated posterior
. end of the heart.

I In the spiders the heart (Jig. 111. a) ex-
j tends, as in flying insects, along nearly the
,' whole of the abdomen, but is wider than in
the scorpion or in insects. It is fusiform,
with thick walls, composed chiefly of trans-
verse muscular fibres, slightly decussating on
the inner surface: a narrow strip of longi-
tudinal fibres extends along the middle of the
dorsal surface.

The blood is returned to the heart by three or four veins (b, b) on
each side : it is propelled forwards by the contraction of the mus-

Heart of Spider.

ARACHNIDA.

259

cular walls, which action can frequently be discerned through the
thin integument of the smaller spiders. M. Duges, w^ho succeeded
in throwing a solution of carmine into the heart from behind for-
wards, found a plexus of vessels at the base of the pulmonary lamellae,
and these productions of the breathing sacs were coloured rose-red by
the injection of their capillaries. Hence it would appear that the
heart of the Arachnida served the purposes of both pulmonic and
systemic circulations, as Hunter discovered to be the function of the
heart in the flying insect. An artery is continued from both extre-
mities of the heart ; the anterior aorta (c) immediately gives off two
transverse branches (d), which Duges regards as pulmonary arteries :
the posterior vessel soon divides into the genital arteries (e). The
venous apertures are bivalvular^, as in the heart of the scorpion. The
heart is situated in all Arachnida, as in the other Articulata, beneath
the dorsal integument and above the alimentary canal. The blood
contains colourless round corpuscules, which have been seen to cir-
culate in the limbs of young spiders ; returning by a less regular
channel than the arterial one ; the veins of the great cavities of the
body are doubtless irregular and wide sinuses.

All true Arachnidans breathe the air directly : the tracheary
respiratory apparatus of the mites commences by a few orifices upon
the abdomen : in the species, parasitic on the Hedgehog (Ixodes
Erinacei)y there are three stigmata ; two near the sides, and one below,
at the middle of the abdomen : the latter is described by Audouin as

a spherical tubercle, pierced by a number
of minute holes, by which the air pene-
trates the tracheae. These air-tubes re-
semble in structure, ramification, and ex-
tensive diffusion, the corresponding parts
in insects.

The spiders of the genera Segestria and
Dysdera have four stigmata, situated on
hi\ the under and anterior part of the abdo-
men : the anterior one on each side {Jig.
112. a) is the aperture of the pulmonary
sac (6); the lower orifice (c) leads to a short
and wide cylinder, from which radiate
numerous trachese (d) having the usual
shining surface. These tubes are united
together in bundles and diverge to the sur-
rounding parts by dissociation, not by true
ramification, like the tracheae of mites and
insects. One bundle is dispersed through-
s 2

112

A^A^/ff^

Respiratory organs, Segestria.

260 LECTURE XIX.

out the abdomen ; another enters the cephalo-thorax, and resolves
itself into groups corresponding in number with the limbs to the
extremity of which the fine silvery tracheae can be traced. The pul-
monary sac (^figs. 112, 113.6), which receives the air by the an-
terior respiratory orifice, is of an elliptical form ; the vascular surface
is augmented by a number of broad and close-set lamellae, which pro-
ject into its interior.

In the scorpion, the stigmata or pulmonary orifices are eight in
number, four on each side of the under surface of the anterior broad
segments of the abdomen. They have the form of oblique fissures,
surrounded by a thickened margin, to which the name of " peritrema "
has been given. The vascular lining membrane of the cavity adheres
to this margin, and is at first simple, but afterwards gives attachment
to a series of broad and close-set lamellae, arranged, as in the spiders,
like the leaves of a book.

The peculiar organs of secretion in the class Arachnida are those
Avhich prepare the material of the web, which is analogous to silk, and
those which secrete the venomous liquid. The former are proper
to spiders ; the latter common to both spiders and scorpions. The
modification of the abdominal segment of scorpions, by which its
hinder half is converted into a slender, jointed, flexible, tail-like ap-
pendage, seems to have special reference to the wielding of the en-
venomed sting. The glands which supply this weapon with its poi-
sonous fluid are lodged in that well-known pyriform dilatation formed
by the last joint of the tail, and which is terminated by the slender
sharp, recurved sting.* A minute slit may be observed near the point,
which is the common outlet of two slender ducts, that gradually dilate
into two secreting sacs, lodged in the cavity of the expanded part of
the joint, and separated from each other by a double vertical partition.

The poison apparatus of spiders is placed at the opposite extremity
of the body. The perforated sting or fang forms the second joint of
the mandible or modified antenna, upon which it has a gynglimoid
movement, and lies concealed and protected when not in use in a
furrow with dentated margins upon the basal joint {Jig. 109. m).
The poison gland is an elongated ovoid vesicle, the exterior of which
is characterised by spiral folds produced by the arrangement of the
fibres of the contractile tunic. The duct traverses the basal joint of
the mandible and the cavity of the fang, and terminates in a fissure on
its convex surface near the point. In the true AranecB, the Clubiones,
and the Lycozce, the poison glands extend into the cephalo-thorax ;
but in the bird-spiders {Mygale) they are limited to the mandibles.
It is probable, therefore, that the effects of a wound occasioned by

* See Prep. No. 2161.

ARACHNIDA.

261

these gigantic spiders may be exaggerated : those species of our
native spider which are most formidably armed, are unable to inflict a
wound on the human skin by any means so painful as the sting of a
bee, but their poison rapidly takes fatal effect upon insects.

The organs which secrete the material of the web are lodged in
the posterior part of the abdomen, and in the Epeira fasciata, which
is remarkable for the large size of its web, they occupy, when in full
activity, about one fourth of the abdominal cavity. They present
the form either of slender and more or less branched tubes, or of di-
lated sacs, the excretory ducts of which terminate upon projecting
jointed organs at the posterior extremity of the abdomen, called
spinnarets. (fig. 112. a.)

In the Cluhione atrox-^ the glands consist of four larger and nume-
rous smaller tubes : two of the larger branched tubes are twice the size
of the other pair. In the genus Pholcus
{JiQ' 113.) the organ is reduced to a more
simple condition ; it consists of six vesicles
of different shapes and sizes ; two {q) are
large and elongated ; they occupy the
middle of the under part of the abdomen,
and their slender ducts are continued in a
tortuous course to the sj)innerets ; two
others (r) are also elongated, but are
smaller than the preceding ; the remaining
two are spherical is). The duct of each
of these glands terminates upon its ajDpro-
priate spinneret, and there are conse-
quently six of these organs.

The Mygale avicularia has only four
spinnarets, and in the Mygale cementaria
YYyQicns ^^^ ^^ them are imperforate. Six, how-

ever, is the ordinary number of spinnarets
in the spiders, two of which are longer than the others. The secre-
tion does not issue by a simple outlet, but by a multitude of micro-
scopic pores_, which, in the shorter pairs of spinnerets, are prolonged
from the terminal surface upon minute processes. If you throw a
little dust upon the web of any of the orbitele spiders, of the Epeira
diadema for example, you may observe that it adheres to the spiral,
but not to the radiated, threads. Lyonnet supposed that the adhesive
threads issued from tubes, and the others from sessile orifices. The
secretion is a glutinous fluid, insoluble in water, and which quickly
dries in air ; some species, as the Argyroneta aquatica^ spread their
nets habitually under water.

s 3

262 ■ LECTURE XIX.

The degree and mode in Avhich spiders exercise this singular
secreting faculty varies considerably in the different species. Some,
as the Clubiones, line with silk a conical or cylindrical retreat, formed,
perhaps, of a coiled-up leaf, and having an outlet at both extremities,
from one of which may issue threads, to entrap their prey. Others,
as the Segestrice, fabricate a silken burrow of five or six inches in
length, in the cleft of an old wall. The Mygale cementaria lines a
subterraneous burrow with the same substance, and manufactures a
close-fitting trap-door of cemented earth lined with silk, and so at-
tached to the entry of the burrow as to fall down and cover it by
its own weight, and which the inmate can keep close shut by means of
strong attached threads.

The arrangement of spiders by M. Walcknaer into families, cha-
racterised by their habits, places the principal varieties of their webs
in a very concise point of view.

The Cursores, Saltatores, and Laterigradce, make no webs ; the
first catch their prey by swift pursuit, the second spring upon their
prey by insidious and agile leaps ; the third run, crab-like, sideways
or backwards, and occasionally throw out adhesive threads to entrap
their prey. The Latebricolce hide in burrows and fissures, which they
line with a web. The TubicolcB inclose themselves in a silken tube^
strengthened externally by leaves or other foreign substances. The
NiditelcB weave a nest, whence issue threads to entrap their prey.
The FilitelcB are remarkable for the long threads of silk which they
spread about in the places where they prowl in quest of prey. The
TapitelcB spin great webs of a close texture like hammocks, and wait
for the insects that may be entangled therein. The Orbitelce spread
abroad webs of a regular and open texture, either circular or spiral,
and remain in the middle or on one side, in readiness to spring upon
an entangled insect. The RetiteltE spin webs of an open mesh-work
and of an irregular form, and remain in the middle or on one side to
seize their prey. Lastly, the Aquitelce spread their silken filaments
under water to entrap aquatic insects.

The silken secretion of spiders is not applied only to the formation
of a warm and comfortable dwelling for themselves, or of a trap for
their prey : it is often employed to master the struggles of a re-
sisting insect, which is bound round by an^i^xtemporary filament, spun
for the occasion, as by a strong cord. Lastly, a softer and more
silken kind of web is prepared for the purpose of receiving the eggs,
and to serve as a nest for the young.

All the Arachnidans are of distinct sexes. Among the spiders,
the male may generally be distinguished from the female by his
smaller size, longer limbs, and brighter colours. The essential and

ARACHNIDA.

263

accessory organs of this sex are quite distinct and remote from each
other ; the principle of such separation, which is exemplified in the
relation of the Fallopian tube to the ovarium in Mammalia, is carried
to an extreme in regard to the vesicula seminalis and testis in the
spiders. If the analogy of the female parts be here, as in other
animals, a guide in the determination of the essential organs of the
male, the testes ought to be the two long vermicular tubes, applied to
the under wall of the abdomen, which commence posteriorly, either
by a simple sac, as in the Mygale, or by an oblong vesicle, as in the
genus Pholcus, the ducts of both of which terminate anteriorly by
two approximate orifices, or else by a common opening, situated be-
tween the two pulmonary stigmata (y?^. 114. k).

The second or copulatory part of the generative organs is confined
to the two last joints of the maxillary palp {Jig- 11 4. c, d) : the
1J4 ,,^,, dilatation of these joints is chiefly formed by a
membranous tube or sac, commencing at the pe-
nultimate and reaching its greatest expansion at
the last joint (d) : this tube appears to line a ca-
vity in the ordinary state ; but it can be distended,
everted, and erected ; when it is seen to be termi-
nated by a horny appendage.

In the female spider the ovarium usually presents
the form of a simple elongated fusiform vesicle {fig-
113. o), closed at one extremit}^ and communicating
with a slender oviduct Qj) at the other, which duct,
after more or fewer convolutions, terminates at the
corresponding angle of the simple transverse vulva.
It is situated, like the outlets of the vasa deferentia,
between the pulmonary stigmata. Each ovarium is
divided in the Epeira, or diadem-spider, by a trans-
verse septum, and the eggs are laid at two distinct periods.

The most careful observations, repeated by the most attentive and
experienced entomologists, have led to the conviction that the ova
are fertilised by the alternate introduction of the appendages of the
two palpi of the male. Treviranus's supposition that these acts are
merely preliminary stimuli, has received no confirmation, and is
rejected by Duges, Westwood, and Blackwall. At the same time,
the most minute and careful research has failed to detect any con-
tinuation of the vas deferens into the terminal erectile sac of the palp,
or any other termination than the abdominal opening above described.
Duges offers the very probable suggestion that the male himself may
apply the dilated cavities of the palpi to the abdominal aperture, and
receive from the vasa deferentia the fertilising fluid, preparatory to

s 4

Tegenaria domestica.

264 LECTURE XIX.

the union. Certain it is that an explanation of this singular condition
of the male apparatus, in which the intromittent organ is transferred
to the remote and outstretched palp, is afforded by the insatiable
proneness to slay and devour in the females of these most predacious
of articulated animals.

The young and inexperienced male, always the smallest and
weakest of the sexes, has been known to fall a victim and pay the
forfeit of his life for his too incautious approaches. The more ex-
perienced suiter advances with many precautions ; carefully feels
about with his long legs ; his outstretched palpi being much agitated :
the female indicates acquiescence by raising her fore-feet from the
web, when the male rapidly advances ; his palpi are extended to their
utmost, and a drop of clear liquid ejected from the tip of each clavate
end, where it remains attached, the tips themselves immediately
coming in contact with a transverse fleshy kind of teat or tubercle
protruded by the female from the base of the under side of the
abdomen. After consummation, the male is sometimes obliged to
save himself by a precipitate retreat ; for the ordinary savage instincts
of the female, " etiam in amoribus saeva," are apt to return, and she
has been known to sacrifice and devour her too long tarrying or
dallying spouse.

There is a redeeming feature in the psychical character of the
female spider, in the devotion with which she fulfils all the duties of
the mother. But before proceeding with the examples of the ma-
ternal instinct, I shall first point out the anatomical characters of the
generative organs in the scorpion.

The palpi of the scorpion take no share in the formation of the
generative system in either sex: both male and female are provided
with a pair of peculiar comb-like appendages, attached directly
behind the genital aperture, which is situated at the middle line of
the under and posterior part of the abdomen. Miiller has observed
that the teeth in the comb of the male scorpion {Buthus Africanus)
are much more numerous and smaller than those in the female ; but
the sexes are not otherwise distinguishable outwardly. The males
appear to be fewer in number than the females.

The testis of the scorpion is a long and slender tubulus, which
divides, and the divisions anastomose together to form three loops or
meshes. A short blind sac ( Vesicula glandularis) communicates
with the termination of the tubulus, and the common duct terminates
in an oblong receptacle, the outlet of which is situated close to the
corresponding one on the opposite side of the body, at the middle of
the under part of the last segment of the thorax.

The tubular oviduct of the female scorpion divides and unites with

ARACHNIDA. 265

its fellow through the medium of a third shorter middle canal, forming
three meshes on each side, and a seventh longer anterior loop by the
terminal union of the oviducts before they open upon the bivalvular
vulva.

The ovaria consist of lateral appendages going off at right angles
from the longitudinal canals_, and expanding into elliptical sacculi
before communicating with the canals : the ova are developed in the
slender blind free extremities or beginnings of the ovaria, and the
embryo is developed in the sacculus, the scorpion being viviparous.
The course of its development, which would be a subject of great in-
terest, has not yet been traced.

Spiders are oviparous. The mother prepares a soft and warm
nest for the eggs, which she guards with great care. The Lycosa
vagahunda carries her cocoon about with her : if it be removed and
a ball of cotton substituted, she has been known to bestow upon it
the same care ; but when the cocoon was offered together with the
cotton ball, she seldom failed to select her own fabrication. The
Saltica selects an empty snail-shell for her cocoon, and spins a silken
operculum across the mouth. The Epeira fasciata incloses her eggs,
which are as big as millet-seed, in a papyraceous cell, surrounded by
a cottony covering, which she then suspends by a dozen threads or
pillars to a larger chamber of silk. The whole is attached to a branch
of a high tree, and is guarded by the mother, who quits it only in
extreme danger, and returns when this is past.

The ovum of the spider, at its exclusion^ consists of a large and
finely granular vitellus, invested by the membrana vitelli, which is
separated from the chorion by a very thin structure of colourless
liquid, analogous to the albumen or the white of the hen's e^g. The
yolk is generally of a yellow colour ; but in some species of spider is
grey, white, or yellowish brow^n. An opake white elliptical spot in-
dicates, at this period, the metamorphosed and impregnated centre
from which subsequent development radiates. The previous changes
which have led to this condition of the excluded ovum have not
hitherto been studied : the subsequent ones, up to the complete for-
mation of the young spider, have been described and figured by the
accurate and industrious Herold.

The germ-spot consists of minute opake whitish granules, of smaller
diameter than those of the vitellus : in some species Herold observed
several germ spots on different parts of the superficies of the yolk,
which rapidly coalesced into one body. Development commences by
expansion of the circumference of the germ-spot, which, as it expands,
covers the yolk with a semitransparent thin layer, the basis of the
future integument. Herold next describes the granules of the germ

266 LECTURE XIX.

as being decomposed into almost imperceptible molecules, in which we
may recognise the ordinary result of the fissiparous property of its
constituent nucleated cells : their powers of assimilation are at the
same time manifested by the changes which they effect in the albumen,
at the expence of which they seem, in the first instance, to increase
their numbers and diffuse themselves over the surface of the vitellus.
This covering of the yolk Herold calls " coUiquamentum ;" he observes
that the original position of the germ-spot is indicated by a clear
transparent point (hyaline ?) ; that this point becomes thickened and
pearly ; then opake, so as to conceal the subjacent vitelline cells. A
similar change progressively extends over the coUiquamentum ; and
when one fourth of the circumference of the yolk is thus covered, the
opake layer has taken on a definite form, resembling the figure 8, the
smaller and anterior division being the base of the future head, the
posterior and larger one, of the thorax. A fissure is next observed to
divide the cephalic from the thoracic portion, the two parts being
distinct at this period, and determining the essential nature of the first
great segment of the body in the mature spider. The margins of the
thorax are next seen to be subdivided on each side by three parallel
fissures into four segments : these are the bases of the epimeral pieces
(^^. 115. 1, 2, S, 4.). The part of the opake integument which
connects the two series below is the rudimental
sternum. A second constriction begins to divide
the thorax from the abdomen; the mandibles or
antennae (b b) begin to bud forth as two con-
vex processes from the anterior part of the head :
the part intervening between these and the epi-
meral pieces forms the rudiment of the maxillee
(c). The intermediate labium also begins to be
defined from the sternum. The opake peripheral
layer (e), extending from the thorax to the op-
Embr>o bpider. positc end of the ovum, lays the foundation of

the ventral integument of the abdomen. Upon the opake integument,
which is extending backwards over the dorsal part of the head, the
characteristic group of simple eyes (d) begins at this time to be dis-
tinctly developed, and the rudiments of the maxillary palps and of the
four pairs of thoracic legs become recognisable : now, also, the dorsal
vessel (/) appears along the upper curvature of the abdomen, and
thus all the chief characteristics of the future spider are manifested,
whilst the great mass of the vitellus remains still visible through the
transparent and incomplete lateral and dorsal parts of the integument.
The constriction between the two divisions of the body increases ;
the legs and palpi next present slight traces of articulations ; as they

TUNICATA, BRACHIOPODA. 267

increase in length they cross the middle line of the sternum, and inter-
lock with those of the opposite side. The mouth, the vent, and the
wide alimentary canal are formed ; the integument is completed, as
in other Articulata, by a dorsal cicatrix, and in this state the young
spider breaks through the attenuated chorion. The head, the man-
dibles, the thorax, and abdomen are first extricated, and afterwards,
but with more difficulty, the palpi and legs are withdrawn. It very
soon has to repeat a similar process in throwing off its foetal integu-
ment, which becomes too small for its rapid growth. This moult
always takes place in the silken nest of the parent ; the young spider
then issues forth, and is subject to repeated moults before acquiring
the mature size.

We perceive, therefore, that throughout the whole process of the
development of a spider, there is nothing worthy to be called a meta-
morphosis. The highest of the Articulata indicates in the feeblest
manner, and can scarce at any period be recognised in the condition
of, the apodal and acephalous worm ; but, with the first rudiments of
trophi and legs, the characteristic or special form is acquired.

The regeneration of the legs of the spider follows precisely the
same law as that which regulates their reproduction in the Crustacea.
If the limb be injured at the tarsus, tibia, or femur, it must first be
cast off at the coxo-femoral joint before the process of reproduction
can commence, and this must be preceded by a moulting of the in-
tegument; the new leg being at first of small size, but with all its
joints and appendages, and acquiring the full proportions at the
second moult.

LECTURE XX.

TUNICATA, BRACHIOPODA.

The Articulate series of animals leads the investigator of the ascend-
ing course of organic development from the vermiform Zoophytes to
the higher organised worms which circulate red blood, and through
the strange and changeable forms of Epizoa and Cirripeda to the
Crustacea, the Insecta, and the Arachnida, in which three classes of
articulated animals with jointed limbs, as many diverging branches
from the common vermiform root, seem respectively to terminate.

Yet having attained these different summits of the articulate branch
of organisation, the enquirer still finds himself at a great distance

268 LECTURE XX.

from any of the Vertebrate forms of animal life. How vast the
hiatus which separates the worm from the apodal fish, the crab from
the tortoise, and the flying insect from the bird or bat I He soon
attains the conviction that there is no regular and uninterrupted
ascent in the scale of organisation, as Bonnet fancied ; no single and
continuous chain of beings, as was sung by Pope.

Not even with the insight which we now command into the living
forms that peopled this planet during past and remote epochs of its
history, can we supply all the hiatuses which exist, and connect
together in a linear series the existing and extinct members of the
Animal Kingdom. But we can discern that many connecting links
in partial series have perished ; and we know that the broken hypo-
thetical chain of being nevertheless continues to flourish and to ade-
quately fulfil its appointed office in maintaining the balance of the
conflicting influences of increase and decay, and the general well-
being and progress of organic life upon the present surface of the
earth.

If we would make a closer approach to the vertebrate type of
organisation, we must retrace our steps, and, again returning to the
Radiata, ascend by another and very different series of animals, from
those which have last occupied our attention.

In the Articulata the advance is most conspicuous in the organs
peculiar to animal life, and was manifested in the powers of locomo-
tion, and in the instincts, which are so various and wonderful in the
insect class.

In the MoUusca the organising energies seem to have been ex-
pended chiefly in the perfection of the vegetal series of organs, or
those concerned in the immediate preservation of the individual and
the species.

The Mollusca are so called on account of the soft unjointed nature
of their external integument. The scattered centres, or Heterogan-
gliate type of their nervous system, is often accompanied with an
unsymmetrical form of the entire body ; which, in compensation for
the low condition of the perceptive energies, is protected in most of
the species by one or more dense calcareous plates, called shells.

The nervous system, as has been explained in the introductory
lecture, consists of a medullary collar, surrounding the oesophagus,
and communicating with more or fewer ganglions near the oesophagus,
or dispersed, usually below the alimentary canal, in other parts of the
body.

In a large proportion of the lower organised Mollusca there is no
head, and no nervous centre is needed above the gullet for the recep-
tion of the impressions received by special organs of sense. The

TUNICATA, BRACHIOPODA. 269

mouth is simply a pharynx or beginning of the oesophagus without
jaws, tongue, or mouth properly so called. Such MoUusca are
termed Acephala. All other Mollusca are provided with a head,
which generally supports feelers or soft tentacula, eyes, and a mouth
armed with jaws.

The acephalous Mollusca are all aquatic, and are divided into
classes according to the modifications of their integument or of
their gills.

The Tunicata are those which are inclosed by an elastic gela-
tinous uncalcified integument ; they breathe either by a vascular
pharyngeal sac, or by a riband-shaped gill stretched across the com-
mon visceral cavity.

The Brachiopoda are defended by a bivalve shell, have two long
spiral arms developed from the sides of the mouth, and respire by
means of their vascular integument or mantle.

The Lamellibranchia are bivalve conchiferous Mollusca, which
respire by gills in the form of vascular plates of membrane attached
to the mantle. The common oyster and mussel are examples of this
best known class of Acephalous Mollusca.

The Encephalous Mollusca are divided into classes according to
the modifications of the locomotive organs.

The Pteropoda swim by two wing-like muscular expansions ex-
tended outwards from the sides of the head.

The Gasteropoda creep by means of an undivided muscular disc
attached to a greater or less extent of the under part of the body.

The Cephalopoda have all or part of their locomotive organs at-
tached to the head, generally in the form of muscular arms or ten-
tacula : in this class only do we find, in the present series of animals,
an internal skeleton. In the rest of the Mollusca the hard parts are ex-
ternal ; but the integument is sometimes uncalcified and flexible, as in
the low organised class which will occupy our attention to-day and
which in this condition of their exo-skeleton afford the parallel to the
cartilaginous state of the endo- skeleton in some of the lowest of the
vertebrate series.

To connect the Tunicata with any of the classes of animals which
we have previously considered, it is necessary to revert to the Polypi,
for it is in this group of the Radiata that we shall find the animals
which have the closest natural alliance with the present class of
Mollusca.

Suppose a Bryozoon to have its ciliated oral tentacula reduced to
mere rudiments, and to have the pharynx enormously expanded, with
its vascular internal surface richly beset with vibratile cilia ; it would
then be converted into an Ascidian, and the transition from the

270 LECTURE XX.

Radiated to the Molluscous series would be effected. But the Brjozoa,
after their larval locomotive stage of existence, became rooted, like
plants, and were aggregated together, forming compound animals ;
and you may be disposed to ask whether any Molluscous animal can
present these Zoophytic conditions. Such do in fact prevail among
the Ascidian Tunicaries. All these low-organised Mollusca, after
a brief period of natation, become adherent to foreign bodies, and
many form groups of individuals united together by a common or-
ganised external integument ; the present order of Tunicata consists,
in fact, of compound and simple Ascidians. I shall first demonstrate
the organisation of this group by these large examples of the simple
or solitary Ascidians *, which do not essentially differ in anatomical
structure from the compound species^ whose small size renders this
a subject for microscopic investigation.

The exterior tunic of the solitary Ascidian is a thick gelatinous or
coriaceous elastic substance adhering by its base, or by a long flexible
peduncle to some foreign body, and perforated at the opposite end or
at the side by two apertures. The exterior of this tunic is sometimes
rough and warty, the inner surface always smooth and lubricous.

The second tunic is muscular ; it adheres to the outer tunic at the
circumference of the two orifices, and is connected to it by blood-
vessels at a few other points ; elsewhere it is quite free, and the op-
posed scirfaces of the intervening space between the muscular and
elastic tunics has the aspect of a serous cavity. Its fine fasciculi of
fibres are remarkably distinct, and are arranged in two layers, the
external circular, the internal longitudinal. The fibres or fasciculi
of the outer layer are smaller than those of the inner one, and less
regularly disposed. They describe regular circles around the pro-
cesses leading to the orifices of the shell. Other fibres of the outer
layer pass transversely from one tube to the other. The longitudinal
fasciculi radiate from the two orifices, and decussate each other,
winding round the bottom of the sac. Deeper, again, than this layer
there is a sphincter surrounding the base of each tube, or orifice, from
which a third more delicate layer of longitudinal fibres are given off".

Of the two more or less protuberant and stellate apertures in the
outer tunic, one leads directly into the muscular sac, the other into a
wide vascular sac contained in the muscular one. The entry to the
vascular sac is defended by a circle of short tentacles. The inner
surface of the sac is marked by parallel and equidistant transverse
lines, the interspaces of which are divided into a series of narrow
vertical compartments : the surface is beset with vibratile cilia. An

* Preps. Nos. 614, 615, 616. 785. 898. b. 998. 1303. c.

TUNICATA, BRACHIOPODA. 271

orifice at the bottom of this cavity conducts by a short oesophageal
canal to the stomach, an oblong dilated sac, with longitudinal folds.
The intestine is disposed in a sigmoid flexure, adheres to the branchial
and muscular sac, and terminates by an anal aperture near the base
of the second orifice of the tunic.

A simple follicular liver is developed from the stomach. In the
Cynthia tuherculata it communicates with the stomach by a single
aperture, from which a groove is continued towards the cardia.

A generative gland, generally dendritic in shape, occupies the
concavity of the intestinal fold, and sends a short and simple duct to
terminate near the anus. In the female Cynthia tuher^cidata there are
two ramified ovaria ; the ovisacs being appended to the branches of a
central stem, passing up by the side of the rectum, and extending over
one side of the branchial sac.

The heart is a simple, elongated, vasiform muscle, inclosed in a
pericardium, attached to the branchial sac ; continued at either end
into a vessel ; the ramification of one being expended chiefly upon
the respiratory organ ; those of the other upon the viscera and tunics
of the body. According to the direction of the circulating currents
the one will be an artery, the other a vein^ and the circulation itself
will be pulmonic and systemic.

The nervous system must be first sought for in the interspace
between the two openings of the muscular tunic ; there you will find
a ganglion from which it is not difficult to trace filaments diverging
to each aperture of the sac where the circular disposition of the
muscular fibres prevails ; other branches accompany the longitudinal
fibres, and supply the respiratory sac ; two contiguous filaments are
continued to the oesophageal orifice.

In the animal manifesting this organisation, which is much richer
unquestionably than the amorphous and rugged exterior would seem
to promise, the only vital actions obvious to ordinary vision are an
occasional ejection of water from the orifices of the tunic by a sudden
contraction, succeeded by a slow and gradual expansion. Such
contractions and expansions, aided by the ciliary currents, which the
microscope has detected, and the peristaltic movements of the ali-
mentary, circulating, and secerning tubes, are all the actions which the
organic machinery has to perform in the living ascidian.

The respiratory currents of sea water with the nutrient molecules
in suspension are introduced by the ciliary action through the
branchial orifice into the pharyngeal respiratory sac, from which the
oesophagus selects the appropriate food. The alimentary excretions
and the generative products are expelled through the anal outlet by
the contraction of the muscular tunic.

272

LECTURE XX.

r^'

In consequence of the space between this and the outer tunic being
closed, that tunic accompanies the muscular tunic in its contraction,
through the influence of the surrounding pressure ; when the muscle
ceases to act, the elasticity of the outer coat begins to restore the
fibrous sac to its former capacity, and the surrounding water flows
into its cavity, either directly or by distending the branchial sac.
We shall find other instances of the economising of muscular force
by the substitution of elasticity as we ascend in the survey of the
molluscous organisation.

In the small compound Ascidians the organisation is essentially
like that of the solitary species, but the viscera are somewhat dif-
ferently disposed : the cavity is longer and narrower, the entire
animal viewed singly being more vermiform.

In Jig. 116., from Dr. M. Edwards' elaborate memoir, the anatomy
of one of the individuals of the species which he has
called Amarouciuin proliferum, extracted from the
common investing tunic, is displayed, a is the proper
or muscular tunic, in which most of the fibres are
longitudinal ; it is much more feeble than in the
solitary Ascidians : c is the oral or branchial orifice :
e, the branchial sac : z, the anal or cloacal outlet ; it is
protected by the overhanging valve 'i, which is re-
quired by the compound Ascidians on account of the
excretory outlet in the muscular tunic communicating
with a common cloacal cavity in the external tunic,
around which the individuals of the composite series
are grouped : j is the ganglion of the nervous system :
k, the short and wide oesophagus : /, the stomach, the
exterior of which is rendered shaggy by the appended
biliary follicles ; m, is the intestine : 7i, the anus : o,
is the heart, which, by its remoteness from the
branchial sac, diff'ers more in relative position from
its analogue in the simple Ascidians than any other
viscus ; it is provided with a pericardium o i p is the
ovarium, p^' an ovum about to escape through the
cloacal outlet, with the embryo ripe for exclusion.
The most important structural difference between the
aggregate and solitary Ascidians is the combination
in the former of a male apparatus with the ovarium.
In Jig. 115. g is the testis : r, the vas deferens, which
terminates at r\ in the common cavity of the muscular tunic.

Some of the compound Ascidians are ramified, and their tunics so
transparent as to permit the movements of the internal organs to be

m

Compound Ascidian.

TUNIC AT A. 273

studied in the living animal. A very singular condition of the circu-
lating system has thus been detected. The blood actually moves
backwards and forwards, to and from the heart in the same vessels,
as it was supposed to ebb and flow in the human veins before Harvey's
great discovery. The oscillation of the currents is not constant and
regular ; the blood is received from the vessel at one end of the heart,
and propelled by a contractile wave into the vessel at the opposite
end : after a true circulation has gone on in this course for a cer-
tain period, a change is observed in the course of the peristaltic
contractions of the heart; the blood for an instant stagnates in
the vessels, and then the wave travels in the opposite direction ;
the heart drives the blood into the vessel from which it had before
received it, and the course of the circulation is reversed. In the
compound Ascidians the vascular systems of the different individuals
anastomose freely with each other.

At first sight it is difficult to conceive how the fixed and compound
Ascidians can multiply their race in situations at a distance from
that which they themselves occupy. This difficulty has been removed
by M. M. Audouin and Milne Edwards, who observed that the young
of the compound Ascidians were not only at their origin solitary and
free, but possessed the power of swimming rapidly by the aid of
the undulatory movements of a long tail. They were seen occasionally
to attach themselves to the side of the vessel of sea-water containing
them, and then to recommence their course, as if to seek a more
suitable point of attachment. After two days of free and locomotive
life, they finally fixed themselves; and, when detached, remained
motionless.

These phenomena are now known to be common to the embryo of
many of the lower sedentary animals. In regard to the Ascidians, it
has been confirmed by M. Sars in the Botrylli of the coast of Nor-
way, and has been more recently observed by Sir John Graham
Dalyell, in a solitary Ascidian of the Frith of Forth.

In the genera Polyclinum and Amaroucium, Dr. Edwards has ob-
served that the ovum, whilst still included in the ovarian mass, con-
sists of the small central germinal vesicle, of a granular vitellus and a
vitelline membrane. In the progress of the ovum to the cloacal
cavity, the yolk acquires a deep yellow colour, the germinal vesicle
disappears, and in its place there is a nebulous speck upon the surface
of the yolk. This is doubtless the remains of the germinal vesicle,
which has come to the surface of the yolk to meet the impregnating
influence, and has undergone the changes by fissiparous multipli-
cation, to which I have so often had occasion to allude. Dr. Ed-

T

274

LECTURE XX.

Larva of Ama-

roucium proli-

ferum.

wards has observed the contact of the spermatic animalcule with the
ova in the cloaca.

The next stage which he records, viz. the granular or
mulberry structure of the vitellus, is the result of the
spontaneous divisions and assimilative powers of the
yoke-cells. The subdivided mass through which the
properties of the hyaline and fertilising principle have
been diffused, is next covered by the expansion of the
germ-spot, forming the basis of the integument. A
process of this integument then begins to extend from
a particular point, and, rapidly elongating, wraps itself
like a cord about the vitellus. This body with its in-
tegument then becomes condensed, and separates from
the chord, which, retaining only its basal attachment to
the pellucid integument, forms the caudal appendage.
The integument {fig. 111. a) increases in thickness.
The extremity of the yolk opposite the caudal attachment
developes a series of cylindrical productions, which re-
minds one of the arms of a polype, but they are few in
number. Three of them have expanded extremities
{b'\ b"), which increase in length ; whilst the other processes di-
minish, and finally disappear. A spiral filament is continued from
the membrane of the vitellus down the centre of the tail (5').

In this state the embryo escapes from the ovum, generally while in
the cloaca of the parent, but sometimes after the e^g has been ex-
pelled from the common central outlet. The young animal immedi-
ately unfolds its tail, and begins to swim like the tadpole of the frog,
which it so much resembles in form. The three clavate cephalic
processes are the organs by which it effects its final adhesion and
settlement. When this has taken place, the tail shrinks, and is
usually detached by progressively increasing contraction at its base ;
— a kind of spontaneous fission.

The sessile and adherent trunk now becomes the seat of an active
development : the integument is thickened ; the yolk becomes elon-
gated and divided by a circular constriction into two unequal parts,
in each of which a clear spot can be recognised. One of these spots,
by subsequent development, becomes the heart ; the other the res-
piratory sac. The subdivided vitelline mass, which now begins to be
rapidly metamorphosed into the special tissues, also acquires a distinct
tunic, which soon separates itself from the thick and gelatinous ex-
ternal integument. The quadrifid orifice of the branchial sac is first
formed upon the internal tunic. The contour of the great respiratory
pharynx can next be discerned, and the constriction of the sac opposite

TUNIC ATA. 275

to the mouth, which indicates the cesophagus. About the same time
may be seen the outline of the anal orifice upon the internal integu-
ment : then the opaque yellow tunics of the dilated stomach, and the
reflected intestine appear ; and below these parts the pulsations of the
large transparent vasiform heart render that organ conspicuous.

The whole of the viscera included by the smooth integument have
been observed to rotate in the cavity formed by the thick gelatinous
tunic, to which the visceral mass again becomes attached by the
adhesion of the muscular tunic at the branchial and anal orifices, and
by the establishment of corresponding orifices in the integument.

Savigny was of opinion that the ovum of the compound Ascidian
contained the germs of all the individuals composing the characteristic
groups in the mature aggregate animal, and that their development
was simultaneous ; but the observations of Dr. Edwards have proved
that a second mode of reproduction, namely that by gemmation, is
superinduced upon the young Ascidian, after the foregoing develop-
ment from the impregnated ovum, which offers an interesting analogy
to the phenomena presented by the polype-larva of the Medusa
The individuals formed by the gemmation of the primary bud of
the young Ascidian, instead of being detached, are retained; the
process of gemmation being regulated so as to produce the charac-
teristic pattern in which the different individuals are grouped in the
mature compound animal.

The gemmation commences by the development of a small tubercle
from the abdominal portion of the internal tunic of the young
Ascidian. This is prolonged, retaining an active circulation in its
interior, and is accompanied by a corresponding growth of the outer
gelatinous integument, which becomes clavate. The process then
bifurcates ; the divisions, in like manner, becoming elongated, ex-
panded and bifurcated at their extremities. Soon the outline of an
Ascidian is sketched in each of these extremities. The primitive
connection with the parent is obliterated ; but the young individuals
remain united together by their primitive peduncle, according to
the law which determines their mode of grouping into systems.
By the progressive increase of their outer gelatinous integument, they
finally coalesce and form the compound mass.

The second order of the class Tunicata includes the Salpiajis,
which float in the open sea, and are characterised by their transparent
elastic outer tunic, which is elongated, compressed, and open at both
extremities. The muscular fibres of the mantle, or membrane lining
the cartilaginous tunic, are arranged in flattened bands. The mouth
and stomach, the liver and the heart, are aggregated in a small mass
or nucleus, near the anterior aperture of the tunic ; the intestine ex-

T 2

276 LECTURE XX.

tends towards the opposite aperture, and terminates freely in the com-
mon cavity of the mantle. A single narrow plicated ribband-shaped
branchia extends obliquely lengthwise across the pallial cavity. The
heart is elongated, and in some species slightly curved and sacculated ;
it communicates with a large vessel at each extremity, one of which is
ramified principally upon the visceral mass ; the other upon the
branchia and the muscular tunics.

From recent observations made by Dr. Edwards on young Pyro-
somata (a compound genus of Salpians), it appears that the circu-
lating currents change their direction periodically, by virtue of
peristaltic and antiperistaltic vermicular contractions of the heart, as
in the Ascidians.

The sexes are distinct in the Salpians, as in the solitary Ascidians.
The ovarium or testis is usually of an oblong form, sometimes single,
sometimes double, adherent to the inner surface of the mantle ; where,
likewise, the embryo is developed.

The only conspicuous vital action in the Salpians is the rythmical
contraction and expansion of the mantle ; in which the elasticity of
the outer tunic antagonises the contraction of the inner one. During
expansion the sea-water enters by the posterior aperture, and is ex-
pelled, in contraction, by the anterior one ; its exit by the opposite
end being prevented by a valve. The reaction of the jet, which is
commonly forced out of a contracted tube, occasions a retrograde
movement of the animal. The currents which successively traverse
the interior of the animal, renew the oxygenated medium upon the
surface of the respiratory organ, bring the nutrient molecules within
the reach of the prehensile subspiral labial membrane of the mouth,
and expel the excrements and the generative products. Thus a single
act of muscular contraction is made subservient by the admirable
co-adjustment of the different organs to the performance of the
functions of locomotion, nutrition, respiration, excretion, and genera-
tion.

Certain genera of Salpians, as the phosphorescent Pyrosoma, are
permanently aggregated into a compound organic whole having a
definite form. All Salpians quit their viviparous parent associated
together in long chains ; after floating for a certain time under this
form the society is dissolved, and each individual, according to Dr.
Chamisso, propagates a solitary young one like itself. This grows to
the size of the grand-parent, and then brings forth a social chain of
young Salpae, which, by the exercise of their uniparous generation,
again give origin to the solitary and multiparous individuals. Thus,
observes Chamisso, only the alternate generations resemble each other.
The case is strictly analogous to the generation of the compound

BRACHIOPODA. 277

Ascidians, of which the solitary young gives origin, by gemmation,
to a compound group, which again procreates, by impregnated ova,
solitary individuals.

Class Brachiopoda. c^, ^.^-^v. z^^Jr m,-z.

These Acephalous Mollusca are deprived, like the Ascidians, of the
power of locomotion, and are attached by a longer or shorter peduncle
to foreign bodies. Their muscular tunic or mantle is, as it were, slit
open, and consists of two broad membranous expansions, called lobes,
which are covered by two calcareous plates, adapted to inclose and
defend all the soft parts of the animal.

The Brachiopoda flourished during the ancient secondary periods,
and are most abundant in the fossil state. Of the few existing genera,
ihc Lingula is characterised by its long peduncle, and the equality of
the valves of its shell, neither of which are perforated : the Orbicula
is sessile, and adheres by one end of a short transverse muscle, which
perforates one of the valves of the shell : the Terebratula is attached
by a short peduncle, which projects through a hole in a beak-shaped
prolongation of one of the valves.

The viscera are situated at the part of the shell next the hinge or
peduncle, and are confined to a very small space in the Terebratula.
The rest of the interspace of the lobes of the mantle is almost entirely
occupied by two long ciliated arms, continued from the sides of the
mouth, and disposed in folds and spiral curves. The bases of the
arms are confluent, and form a transverse fringed band above the
mouth ; a narrow parallel fold of membrane passes below the mouth,
Avhich opens upon the mantle-lobe attached to the perforated valve.

In the Terebratula australis each arm extends outwards, advances
forwards, curves slightly inwards, and bends abruptly back upon
itself, the two parts of the bend being connected together: then the
stem again curves forward, and becomes united to the corresponding
bend of the opposite arm, the conjoined extremities describing spiral
convolutions turned towards the dorsal valve : the bent portions of
the fringed arms are supported by slender and elastic calcareous pro-
cesses. Remains of more complicated internal calcareous appendages
are presented by certain extinct Brachiopods, as the Spirifer. In
some species of existing Terebratula, as Ter. psittacea, the arms are
disposed in a series of spiral folds; but they have only short and
simple calcareous processes at their base. The spiral arms of the
OrbiculcB and Lingulce have no internal calcareous support. In all
the Brachiopods the stem which supports the braciiial fringe is

T 3

278 LECTURE XX.

hollow. In the Terebratulce and OrbiculcB the spiral terminations of
the arms have their central canal surrounded by a double oblique
series of muscular fibres : the canal is filled with fluid, and, by the
contraction of the muscular fibres, the extremities are extended by
the pressure of the contained fluid which is injected into them.

The alimentary canal is very short and simple : in the Terebratula
it soon expands into a gastric cavity, surrounded by groups of the
minute hepatic follicles, included in the peritoneal membrane behind
the base of the arms. The stomach bends, and is continued in a
short and straight intestine, which terminates between the lobes of
the mantle, on the right side. A small transversely plicated membra-
nous process is continued from each side of the beginning of the
intestine.

The principal centres of the vascular system are two dilated sinuses
or ventricles, situated on each side of the visceral mass, and commu-
nicating by one extremity with the vessels which ramify over the
lobes of the mantle, and by the opposite extremity with those which
supply the viscera. In the Terebratula and Orbicula, the respiratory
function would seem to be performed chiefly by the pallial vessels;
and in this conclusion we are supported by observing the prolongation
of vascular loops from the pallial vessels in the Lingula, which
afl'ords the only indication of distinct branchial organs in the class
Brachiopoda. The margin of the mantle is fringed with cilia, which
are very long in the Lingula and Orbicula. In the latter Brachiopod
I found them beset with smaller cilia: these, with the brachial
fringes, and the microscopic vibratile cilia, which, doubtless, beset
the whole surface of the vascular mantle, must be the chief agents in
introducing the currents of sea water within the cavity of the mantle
for nutrition, respiration, and excretion.

A nervous collar, with small ganglionic enlargements, surrounds
the oesophagus in the Terebratula, as in the Lingula and Orbicula,
Nervous filaments are continued from this centre to the adductor
muscles, and to the vascular lobes of the mantle.

In the Terebratula, two pairs of muscles arise from each valve,
some of which are attached to the opposite valve, and others lost in
the pedicle. The pedicle is surrounded by an elastic yellow horny
layer and a tubular prolongation of the mantle. In the Orbicula
there are eight distinct muscles adapted for closing the shell, sliding
the valves upon each other, and attaching them to foreign bodies.

In the Terebratula and Orbicula the ovaria are dendritic, and
attached to the mantle, four on the lower and two on the upper lobe :
the ova appear to be developed from the inner surface of the large
and wide pallial veins, to the parietes of which they adhere. The

BRACHIOPODA. 279

testes in the male have the same form and disposition : they differ
from the ovaria in their closer texture and their whiter colour.

On comparing together the three existing genera of Brachiopoda
which hav^e been selected for anatomical demonstration in the present
Lecture, we may perceive that the modifications which are traceable
in their respective organisations bear relation to the different situ-
ations which they occupy in the sea.

The Lingula, living usually near the surface, and sometimes where
it would be left exposed by the retreating tide, if it were not buried in
the sand of the shore, must meet with a greater variety and abundance
of animal nutriment than can be found in the deeper waters, where
the Terebratula usually resides. Hence its powers of prehension are
greater ; and Cuvier suspects that it may even enjoy a species of
locomotion from the superior length of its peduncle. The organisation
of its mouth and stomach indicates the molecular character of its
food; but its convoluted intestine shows a capacity for extracting a
quantity of nutriment proportioned to its superior activity and to the
greater extent of its soft parts. The more obvious and complex
respiratory apparatus is in exact harmony with the above conditions
of structure and habits.

With regard to the Orbicula, and more especially the deep sea
species of Terebratula, both the respiration and nutrition of such
animals which exist beneath a pressure of from sixty to ninety fathoms
of sea water, are subjects suggestive of interesting reflections, and lead
one to contemplate with less surprise the great strength and com-
plexity of some of the minutest parts of the frame of these diminutive
creatures. In the unbroken stillness which must pervade those
abysses, their existence must depend upon their power of exciting a
perpetual current around them^ in order to dissipate the water already
laden with their effete particles, and to bring within the reach of
their prehensile organs the animalcules adapted for their sustenance.
The actions of the Terebratula and Orbicula, from their attachment
to foreign bodies, are confined to the movements of their brachial
and branchial filaments, and to a slight divarication and sliding mo-
tion of their protecting valves ; the simplicity of their digestive ap-
paratus, the still greater simplicity of their branchiae, and the
diminished proportion of their soft to their hard parts, are in harmony
with such limited powers. The soft parts, in both genera, are, how-
ever, remarkable for the strong and unyielding manner in which they
are connected together. The muscular system is much more complex
than in ordinary bivalves, and is remarkable for the compactness of
its fibre and the density of the glistening tendons. Here is obviously
an apparatus of sufficient power to effect the requisite motions of

T 4<

280 LECTURE XXT.

the valves at the depths at which they may be destined to live. The
Terebratula, in this respect the most remarkable of Bivalves, has an
internal skeleton superadded to its outward defence, by means of
which additional support is afforded to the shell, a stronger defence
to the viscera, and a firmer basis of attachment to the spiral arms.

LECTURE XXI.

LAMELLIBRANCHIATA.

The relation of the contained soft parts to the bivalve shell of the
Brachiopoda is such that, in the Terebratula, the perforated valve
must be regarded as the inferior or ventral one, and the imperforate
or shorter valve the dorsal one. In the Lamellihranchiata one valve
is applied to the right, and the other to the left, side of the animal.
In the common oyster and the Anomia, which are fixed and mo-
tionless, as in the Brachiopoda, the two lobes of the mantle are as
little united with each other, and there is as little evidence of any lo-
comotive organ or foot. The spiral brachia would seem to be reduced
to two shorter and more simple processes^, and the inferior labial fold
to be produced on each side to the same length, so that there is a pair
of labial processes on each side the mouth. These appendages have
no internal calcareous support, which, by being bent, could open the
valves ; nor are they long enough, save in some species of Anomia,
to be protruded from the shell. In other Lamellibranchiate Bivalves
the labial processes are short and simple. In all the present class
the divarication of the valves is provided for by the insertion of an
elastic substance at their hinge ; and the valves are closed by the
contraction of short and thick subcircular muscles, thence called
the adductors. In the common oyster, and some other allied Bivalves,
there is but one adductor muscle. The visceral mass occupies about
half the cavity of the shell next the hinge. The rest of the interspace
of the pallial lobes being almost wholly occupied by the branchial
laminae, which are four in number, of a crescentic figure, placed two
on each side of the visceral mass. This is the characteristic condition
of the respiratory organs in the present class of Acephalous Mollusca,
and from which it derives its name.

In the oyster the mouth is continued by a short oesophagus to an
expanded stomach, from which numerous ramified hepatic follicles
are developed. The intestine, after describing a few convolutions, is

L AMELLIBRANCHI AT A. 281

continued along the interspace of the branchiae towards their extre-
mities which are furthest from the mouth. The ovarium or the testis
surrounds the intestinal convolutions, and forms with the liver the
chief part of the visceral mass.

The veins of the oyster terminate in a single auricle, which trans-
mits the blood to a pyriform ventricle ; the two divisions of the
heart being contained in a distinct pericardium, situated between the
visceral mass and the concave margin of the adductor muscle.

The principal centre of the nervous system lies upon the opposite
convex margin of the same muscle^ supplies it with nervous influence,
distributes branches to the mantle, to the gills, and sends forwards
two long filaments, parallel with each other, one on each side of the
visceral mass, to the sides of the mouth, where they form small
ganglions, communicating with each other by a transverse branch
above the mouth, supplying the labial processes, and forming a second
feeble communicating arch beneath the mouth, from which the
gastric nerves are continued.

Most of the Lamellibranchiate Bivalves are free and locomotive.
The instrument by which they move from place to place is a single
symmetrical muscular organ developed from the ventral surface of
the visceral mass. The body and protecting shell is longer in pro-
portion to its depth in these locomotive bivalves ; and there are two
muscles provided for closing the valves. The superadded one is an-
terior to the mouth ; the analogue of that which exists in the oyster
being the posterior adductor.

The bivalves with one adductor muscle are termed " monomyaries ; "
those with two adductors " dimyaries." The dimyary bivalves have
always a foot ; in its least developed condition it is subservient to
the function of a gland which secretes a glutinous material analogous
to silk, the filaments of which serve to attach certain bivalves, as the
Pinna and the common mussel, to rocks ; these filaments are termed
the "byssus."

In most dimyary bivalves the foot is a true organ of locomotion.
To some which rise to the surface of the water, it acts, by its expan-
sion, as a float ; to others it serves, by its bent form, as an instrument
to drag them along the sands ; to a third family it is a burrowing
organ ; to many it aids in the execution of short leaps.

We may generally observe in relation with the greater development
and more active functions of the foot, a corresponding complexity of
the respiratory system. This is generally eff'ected by the superaddition
of accessory organs in the form of tubular prolongations of certain
parts of the margin of the mantle, which are provided with a
special development of muscular fibres forming tubes called ''siphons,"

282

LECTUKE XXI.

which require for their retraction special muscles attached to the
valves of the shell : in the Pholas crispata there is a third small ac-
cessory gill on each side.

In the Ve7ius chione {Jig. 118.) we have an example of one of

Venus chione.

these highest organised of the acephalous Mollusca, in which the
characters of its grade of structure are indelibly impressed upon the
valves of the shell. The muscular fibres («, a) which retract the
margins of the mantle have their fixed point within the margin of the
shell, and leave there a linear impression at a' : the adductor muscles
leave deeper impressions : b is the anterior adductor, and b' its corre-
sponding impression : c is the posterior adductor, and c' its cor-
responding impression : d is the retractor of the siphons, and d' its
corresponding impression : e shows the transverse fibres of the foot,
which, by thin contraction, lengthen the organ, and cause it to pro-
trude : / marks the longitudinal fibres or retractors of the foot.
When the siphons are present, they are always two in number, corre-
sponding with the oral and anal apertures in the tunic of the
Ascidian : in Jig. 118., g is the inhalent, and g' the exhalent, siphon.
The labial processes arc shown at h : the stomach at i. A remarkable

LAMELLIBRANCHIATA. 283

elongated amber-coloured body, called the crystalline style, is indi-
cated at k : it is contained in a special cyst, with its free extremity
protruding into the stomach ; it is peculiar to certain species of
dimyary bivalves, and its use is unknown. The intestine {l) forms
a few convolutions, and terminates in the rectum (?«), which per-
forates the ventricle of the heart {ii). The blood is received from
the veins of the gills (jt?) in this, as in all other dimyary bivalves, by
two auricles (o, o), which transmit their contents to the single fusiform
ventricle, perforated in the remarkable manner just shown. In the
genus Area, which is remarkable for its great breadth, the ventricle
itself is divided into two cavities, having the rectum in the interspace.
An artery is continued from each extremity of the ventricle, which
distributes the oxygenated blood over the viscera, the muscular
system, and the mantle.

The branchial plates are essentially internal folds of the pallial
membrane, and are strengthened by series of delicate jointed fila-
ments, which support as many series of curved vibratile cilia. The
respiratory currents are occasioned by the ceaseless action of these
cilia, and are not dependant upon any opening or closing of the
valves of the shell. The ciliary action is that likewise which brings
the nutrient molecules to the mouth.

The two branchial lamellae of one side are usually connected with
those of the opposite side by their posterior extremities only ; but
sometimes the union is more extensive. In a few genera, as Afiatina
and Pholadomya the two lamellae of the same side are so united as to
appear like a single gill. In the Pholadomya it forms a thick oblong
mass, finely plicated transversely, attenuated at both extremities,
slightly bifid at the posterior one. A line traverses longitudinally the
middle of the external surface, which has no other trace of division.
The branchiae on each side adhere to the mantle by the whole of their
dorsal margin, and are united together where they extend beyond the
visceral mass, being separated, by the interposition of that mass,
along their anterior two-thirds. A narrow groove extends along the
free anterior margins of each gill. When the inner side of this ap-
parently simple gill is examined it is seen to be divided into three
longitudinal channels, by two ridges, containing the vascular trunks
and nerves of the gills. A style passed from the excretory siphon,
behind the conjoined extremities of the branchiae, enters the dorsal
channel, from which the excretory respiratory currents are discharged :
the middle channel is characterised by an orifice which conducts into
the cavity of the gill, where the ova are hatched : the third channel
forms the inner or mesial surface of the gill, which is not otherwise
divided.

284 LECTURE XXI.

The returning veins of the body form a remarkable plexus at the
base of the gills, near the pericardium, which assumes the form of a
distinct glandular organ in the higher bivalves. The secretion of this
venous body abounds with calcareous particles, and the gland was
called by Poli the secreting organ of the shell : it is shown at
fig. 118. i\ Modern analysis has detected a large proportion of uric
acid in the peritoneal compartment enclosing this venous plexus, and
has thus determined it to be the renal organ.

The nervous system advances in a regularly proportional degree
with the complexity of the general organisation, and especially with
the muscular system : the ganglion upon the posterior adductor,
which is most conspicuous in the oyster, is the largest and most
constant in all other bivalves : it supplies the branchiae with their
nerves, and when these are approximated on each side, it is single ;
when they are wider apart, it is double. It is called, therefore, the
branchial ganglion, but it distributes an equal share of nerves to the
posterior and dorsal parts of the mantle.

In the common mussel the labial ganglions may be distinguished
by their yellow colour at the base of the labial processes. They are
connected by a short transverse nervous chord, passing above or in
front of the mouth. From each of the ganglions two principal nerves
are given off, one passing forwards to the anterior adductor, the other
backwards along the base of the foot and the visceral mass to the
posterior adductor. At a short distance from the labial ganglion,
this latter nervous chord sends off a branch, which communicates
with its fellow by means of a bilobed ganglion, situated at the anterior
part of the base of the foot. This pedial ganglion and the labial and
branchial ganglions just described, constitute the principal centres of
the nervous system in the common bivalve here dissected with so
much elaborate minuteness by Mr. Goadby. The pedal ganglion
distributes nerves in one direction to the retractors ; in another to the
substance of the foot. The branchial ganglions send off nerves
which are distributed principally to the posterior pair of the breathing
organs, and two large nerves which diverge as they pass over the
adductor muscles to proceed to the base of the tentacular processes
guarding the posterior lobes of the mantle : these continue along
the margin of each lobe of the mantle until they meet and anas-
tomose with corresponding branches, which are continued over the
anterior adductor muscles from the labial ganglions. Cuvier ac-
curately describes this important feature in the nervous system of the
bivalves. The marginal pallial nerve is not, however, simple, but
consists rather of a series of elongated loops.*

* Many other particulars of the nervous system of the Mytilus, demonstrated in

LAMELLIBRAXCHIATA. 285

The nerves of this and other bivalves present the soft and pellucid
structure which is so common in the aquatic invertebrata. The mo-
dification of the nervous system, in other bivalve mollusca, have been
ably compared and reduced to their analogues by Mr. Garner. In
the oyster the suboesophageal loop is slender and contracted, and
unconnected with any other ganglion excepting the labial ones in the
pedate bivalves ; the suboesophageal loop is more or less lengthened,
having the form of a Roman arch in the Pecten, and that of the
Gothic or pointed arch in the Cardium and Mya ; it has for its key-
stone, if we may pursue this analogy, the pedial ganglion. In some
species this ganglion is more distinctly bilobed than in others ; some-
timesj as in the Pholas, it is situated more superficially near the tip
of the foot ; in all it seems to be the centre from which the viscera
derive their nerves. The largest and most constant ganglions are
those situated upon the posterior adductor muscle, following this
muscle in all its varieties of position, and manifesting likewise dif-
ferences in relation to the branchise, but always brought into direct
communication with the oral or labial ganglions.

In these bivalves, as the Ostrea, Cardium, Unio, Anomia, Vejius,
PholaSi Teredo, Solen, Mya, and Mactra, in which the gills of
one side are united to those of the opposite, the branchial ganglia
are conjoined. But in those, as the Mytilus, Modiola, Pecten, in
which the branchia are separate, and at a distance from one another
the two ganglia are distinct, and joined by a transverse chord of
greater or less extent.

A small siphonic ganglion is developed at the point of confluence
of the muscular respiratory tubes in tlie bivalves which possess those
accessory organs of respiration.

Dr. Siebold has recently described a small sacculus in the Cyclas
cornea, attached to the anterior part of the labial ganglion, and con-
taining a cretaceous nucleus of a crystalline structure, performing
remarkable oscillatory movements : this sac he regards, with much
probability, as a rudimental organ of hearing. The Pecten has a
number of small ocelli arranged around the inner margin of the ,
mantle, and which have been regarded from the period of Poli, who
called the Pecten Argus, as rudimental organs of vision. Oysters
appear sensible of light, and close their valves when the shadow of
an approaching boat is thrown forward, so as to cover them before

the beautiful dissections and drawings exhibited, were detailed by the Professor,
under the names of the " pre-pallial," and " post-pallial nerves ;" the " circumpallial
plexus," the " dorso-pallial plexus," the " visceral nerves," " branchial plexus," &c.,
the special description of which, with figures, would, he stated, shortly appear in a
monograph directed to be published by the Council of the College. W.W, C.

286 LECTURE XXI.

any undulation of the water can have reached them. The labial
palpi seem well adapted, both by structure and position, to exercise
the sense of smell ; but of the existence of this sense, or of taste, we
have no proof. The mantle is highly susceptible of impressions by
contact.

Between the freely open state of the mantle in the oyster and
similar monomyary bivalves (^Ostracea), and its condition in the
dimyary bivalve ( Ve?ius) selected for the demonstration of the general
organisation of the LamelUbranchiata, there are intermediate modifi-
cations. The common mussel is the type of a family (^Mytilacea) in
which the mantle is widely open anteriorly, the margins of the lobes
being united together posteriorly, except for a small space forming
an outlet for the excrements. In the Chamacea the margins of the
pallial lobes coalesce, leaving a small anterior aperture for the foot, a
second smaller one for inhaling the respiratory and nutrient currents,
and a third posterior orifice for excretion. The family typified by
the Venus has the two latter orifices produced into a siphonic tube, and
the anterior or pedial aperture corresponds in width with the supe-
rior size of the foot. The modifications of the mantle are essentially
the same in the family called Incliisa ; but the narrower and longer
figure of the body occasions a greater proportion of the confluent
margins of the mantle between the anterior pedial and the posterior
siphonic apertures, whereby the mollusc, especially when the foot is
small, becomes inclosed in a membranous tube or sheath. The
most essential diff'erence is presented by the Pholadomya, which has,
besides the pedial and two siphonic apertures, a fourth orifice at the
under part of the base of the siphon, leading by a valvular protuberance
into the interior of the pallial cavity. This additional aperture co-
exists with a second small muscular process or foot, which is bifur-
cate at the extremity.

The bivalve shell of the Palliobranchiata offers, as might be
expected, many modifications corresponding with those of the mantle.
The shell consists essentially of an organised extravascular com-
bination of gelatinous membrane and calcareous earth, chiefly car-
bonate of lime, arranged in successive layers, the innermost being
the largest and latest formed ; and each layer presenting a cellular
or fibrous texture, which presents characteristic variations in different
families.* The distinction between the internal or nacreous layers.

* The microscopic structure of shells has formed the subject of the investigations
of a committee of the Microscopical Society of London, and of the independent and
original observations of Dr. Carpenter, The results of these inquiries will form a
valuable addition to the anatomical history of the Mollufca, and to the physiology
of the extravascular tissues in general. R. O.

LAMELLIBRANCHIATA. 287

and the external or fibrous layers, has long been recognised, and has
been forced, as it were, upon the notice of the palaeontologist by the
circumstance of the two being often separated from each other in
fossil shells, and sometimes from one having perished whilst the other
remained. As the nacreous layer alone forms the characteristic
hinge uniting the two valves of the shell, and alone receives the im-
pressions of the soft parts, the true characters of fossil shells, as those
of the genera Podopsis and Spherulites, which, in consequence of
their position in porous chalky beds, have lost all the nacreous layer,
cease to be determinable. When the inner layer is preserved, its
impressions reveal the organisation of the ancient fabricator of the
shell as clearly as do the forms and processes of fossil bones that of
the extinct vertebrate animal.

The siphon in some of the elongated Inclusa cannot be retracted
into the shell ; they are consequently exposed, as in the Pholadomya
and Pholades : such species derive extrinsic shelter by burrowing in
sand or stone. The Pholades have supplemental calcareous pieces in
the hinge of the shell. The ClavagellcB and Aspergilla line their
burrows with a calcareous layer, which forms in the latter a dis-
tinct tube, closed at the larger extremity by a perforated calcareous
plate. One of the valves of the normal shell adheres to the tube
in the Clavagella^ and both are cemented to its inner surface in the
Aspergillum,

In the Teredo, or Ship-borer, the most vermiform of molluscous
animals, the valves are reduced to mere appendages of the foot, at
one extremity of the animal, and are restricted in their function to
the operation of boring. As the ship-worm advances in the wood it
lines its burrow with a thin layer of calcareous matter. The length
of the body is chiefly due to the prolongation of the respiratory tubes,
each of which is provided with a small elongated calcareous triangular
plate. In the Teredo gigantea the tube, which sometimes surpasses
six feet in length, has parietes of from four to six lines in thickness,
the texture of which is crystalline or spathose.

The valuable pearls of commerce are a more compact and finer
kind of nacre, often developed in the substance of the mantle, or
around a particle of sand or other foreign body which has gained
admission to the pallial cavity. The Meleagrina or Avicula mar-
garitifera of the Indian seas is most famous for these productions.

The latest and best observations of naturalists and physiologists on
the sexual characters and generation of the Lamellibranchiata have
established the correctness of Leuwenhoek's conclusion that these
moUusca are of distinct sexes, some individuals being male and others
female. In the small species of Ariomia parasitic upon fuci on the

288 LECTURE xxr.

south coast of England, I have found the males and females nearly
equal in number, the males being distinguished by their opake white
testis abounding in spermatozoa, the females by their yellow or orange-
coloured ovarium. There appears indeed to be only one observed
exception to the dioecious condition, namely in the Cyclas, in which
Wagner found, in addition to the ovaria, an isolated pair of testes.
In the males the testes are double and have a somewhat more cir-
cumscribed form than the ovaria, but sometimes appear to be blended
together at the median line : in the oyster they are situated on each
side of the liver, and extend in the form of a triangular process be-
tween the adductor muscle and the gills. The testes extend at the
breeding season in certain genera, as Mytilus and Modiola, into the
substance of the lobes of the mantle ; but in those bivalves which
have a large foot, the testes are confined to the base of that organ.
The ultimate texture of the testes is a congeries of vesicles con-
taining a milky fluid, which seems to consist almost wholly of sper-
matozoa in the breeding season. The vasa deferentia are short and
wide, and they open behind the mouth in the oyster, and terminate
upon papillae at the posterior part of the foot in most dimyary mol-
lusca, as the Cardium. Pholas, Venus, &c.

The ovaria have a similar form and position in the female bivalves,
but are usually more extensively ramified. At all seasons of the year
some ova may be discerned in the ovarian cells, characterised by the
germinal vesicle and spot. Towards the breeding season they are
developed in immense numbers ; and the addition of the coloured
vitellus to the essential part of the ovum gives the characteristic
colour to the ovaria. They are generally distended with the ova
in the winter months. The fertilising filaments retain their in-
fluence after being discharged from the males ; are drawn in with the
respiratory currents, and at the breeding season the ovaries and
oviducts contain a milky fluid abounding
^v with the moving filaments. The ova then
escape by the short oviducts, which ter-
minate in positions analogous to those of
the vasa deferentia. They are conveyed
along the basal margin of the internal
branchiae, enveloped in mucus, from the
oviducts to the posterior terminations of
the inter-branchial space, where they en-
ter the canal which traverses the base of
the external gill, and pass into the recep-
tacles formed by the interspaces of the
transverse lamellae, connecting the outer

LAMELLIBRAXCHIATA. . 289

with the inner wall of this gill. In/^.119. is shown a transverse sec-
tion of the right lobe of the mantle («), and of the right pair of
gills in a fresh-water muscle (^;^of/o;i), at the period when the external
gill is performing its marsupial function, and is laden with the ova :
h is the inner gill, c the outer gill, showing the basal canal and the
free margins of the partitions of the branchial cells in which the ova
are incubated.

The development of the ovum takes place in this temporary
marsupium : it has been studied by Cams in the Unio and by Quatre-
fages in the Anodon. Fig. 120. a shows the ovarian ovum of the
120 Unio litoralis before impregnation : the germinal vesicle
is seen at a, the coloured vitellus with the membrana
vitelli at ^, the albumen at c, covered by the chorion.
Before the ovum reaches the branchial marsupium, the
germinal vesicle has undergone the ordinary changes
which lead to its apparent destruction: the albumen in-
creases in quantity: pentagonal and hexagonal epithelial
cells are developed upon the surface of the vitellus, as
shown in^^. b. ; vibratile cilia are developed upon them.
'Movements in the albumen are then observed in the vi-
cinity of these cells. They extend over the yolk ; the
currents in the albumen increase in strength, and, finally,
the yolk itself begins to revolve in the surrounding fluid.
This singular phenomenon was observed by Leuwenhoek in 1695.

Two parallel fissures next make their appearance, which, sinking
deeper into the yolk, divide that part, which is now included in
the rudimentary digestive sac, from the lobes of the mantle.
Calcification commences on the outer surface of these lobes, and
the first layer of the future shell forms a small triangular valve
on each side. When the rotation of the embryo is most active,
seven or eight revolutions may be observed in the minute. The
gills make their appearance as minute processes from the inner
surface of the mantle, near the angle between the pallial lobes and
the visceral mass. The development of the adductor muscle, single
at the beginning and near the hinge, is indicated by feeble actions of
opening and shutting the valves. The albumen during this develop-
ment is absorbed and assimilated ; and the embryo now distends the
chorion. In the young Anodon, long filamentary processes, twisted
together like a byssus, are developed from the visceral mass, which
mass seems to shrink in size as the lobes of the mantle and valves of
the shell increase. The thick, short, fleshy foot is subsequently de-
veloped in place of the byssiform filaments.

The young Uniones and Anodontes escape from the chorion before

290 LECTURE XXI.

they quit the marsupium, and may be observed swimming freely about
in the cavity of the external gill. They were mistaken for parasitical
animals by Rathke, and described by him under the name Glochidium;
and the difference of form between the young and the old Anodontes
was such, that Professor Jacobson adopted the same opinion, con-
sidering it to be improbable that they could be the offspring of the
animal in which they were found. In fact, besides the byssiform ap-
pendage which characterises the young Anodon^ the valves are, at first,
triangular, with one side short and straight, where they are united by
the ligament, and the other two sides meet, and terminate in a point,
beyond which a process of the mantle is continued, which is dentated .
on its outer surface : two pointed processes project from the inner
surfaces of the valves. The entire amount of change effected in the
progressive acquisition of the mature form merits the name of a me-
tamorphosis.

The course of the intrabranchial development of the young Anodon
extends over two, three, or four months : the young sometimes escape
from the parent as late as in September. The young animal, after
exclusion^ uses the prehensile or adhesive filament to anchor itself to
the shell of the parent, or to some foreign body.

In the genus Cyclas, ]Mr. Garner * has observed from ten to twenty
of the young fry, situated in the internal branchiae : they are discharged
one by one when they attain about the sixth of an inch in diameter.
The oviducts in the Cyclas open over these internal branchiae, and
are only accessible to the w^ater from behind, as are the external
branchiae of the Unio. The young Cydades are sometimes found
adhering by a byssus to different parts of the body of the parent.
The young of the genus Naias have been observed to anchor them-
selves after exclusion from the parent, by a byssus, which is usually
wanting in the large and full-grown animals.

This temporary means of attachment must prevent many of the
young and feeble bivalves from being carried away by the stream at
a period when their shell has not attained sufficient hardness to
protect them from the numerous predatory aquatic animals to whose
attacks they would be exposed ; and we may thus discern, in the de-
ciduous byssus, an evidence of prospective design for the well-being
of the weak and defenceless.

* Zoological Transactions, vol. ii. p. 97,

PTEROPODA. 291

LECTURE XXII.

PTEROPODA AND GASTEROPODA.

Although the Acephalous Mollusca are for the most part deprived
of the power of locomotion, or have it granted to them in a very low
degree, yet some species of Lamellibranchians can swim, and the
pectens, from their lively movements in the water, and the vigorous
flappings of their brightly tinted valves, have obtained the name of
sea-butterflies. Amongst the Mollusca provided with a distinct head,
locomotion is the rule not the exception. The Lithedaphus is fet-
tered by its calcareous operculum to the rock on which it grows, and the
Magilus becomes immoveably sunk in its coral bed. Certain extinct
genera of the family Rudistes, allied to the Ccdyptreid(B, were also
sedentary ; but all the other encephalous Mollusca are free and loco-
motive : some creep, some climb, some swim : a few combine these
different powers ; whilst certain small species have no other mode of
progression than by floating or swimming on the surface of the
ocean. These are provided with two fin-like muscular expansions,
attached to the sides of the neck, which, from their resemblance to
wings, suggested to Cuvier the name Pteropoda for this small and
lowest organised class of the encephalous Mollusca.

Some Pteropods are provided with a light and delicate semitrans-
parent shell. In the Hyalcea^ it resembles a bivalve shell, of which
the two valves had been cemented together at the hinge ; leaving a
narrow fissure in front and at the sides. In the Cleodora, the two
plates of the shell are united together along the sides as well as at the
base, leaving an opening only in front. The shell of the Limacina
is a cone twisted spirally in one turn and a half. The shell of the
Cymhulia is symmetrical, like a boat or slipper, but is cartilaginous,
'i'he Clio and Pnewnodermon are naked, or without shells.

All the species of Pteropoda are of small size ; they float in the
open sea, often at great distances from any shore, and serve, with the
Acalephae, to people the remote tracts of the ocean. In the latitudes
suitable to their well-being, the little Pteropoda swarm in incredible
numbers, so as to discolour the surface of the sea for leagues ; and
the Clio and Limacina constitute, in the northern seas, the principal
article of food of the great whale.

Those Pteropoda which have symmetrical shells composed of two
plates have one applied to the dorsal, and the other to the ventral,
surface of the body, as in the Brachiopoda ; and the two muscular

u 2

292 LECTURE XXII.

cephalic expansions may be regarded as analogous to the large arms
of those Acalephae : but the Pteropods manifest a much higher grade
of development in having a distinct head, with tentacula and jaws
anterior to the attachment of the wing-like expansions. In the
Hyalaea, the head and fins form together a large division of the body,
which has been compared to a cephalo-thorax ; the part containing
the viscera and which is lodged in the shell forming the abdomen.

In this species the upper or dorsal valve is nearly flat, and is pro-
longed anteriorly beyond the ventral plate, which is convex. Thin
lobes of the mantle correspond with the divisions of the shell, but are
united together at the sides ; from which long membranous processes
are continued in some species. The principal part of the muscular
system arises by a narrow tendon from the posterior point of the
shell, passes forward through the abdomen between the ovary and
branchia, expanding as it approaches the head, where the fibres de-
cussate, and diverge in the substance of the fins : other strata of
muscular fibres decussate the preceding obliquely.

The mouth is a small longitudinal fissure, at the apex of two
diverging labial eminences : it contains a lingual prominence, covered
by a thin uncinated horny plate. In the Clio the tongue is more
prominent, and is beset with transverse rows of recurved hooks ; and
the mouth is provided with two small lateral jaws, supporting a row
of unequal horny teeth. * Salivary glands coexist with the maxillary
organs in the Clio; they are wanting in the Hyalcea. In both
Pteropods the stomach is large and globular, the intestine disposed in
three or four coils, and terminating at the right side, and towards the
anterior part of the mantle. The liver is voluminous, in part conceal-
ing the stomach, but transmitting the bile by a single duct to the be-
ginning of the intestine. In the Pneumodermon the biliary secretion
is said to be poured into the stomach by many pores ; as, in the ace-
phalous bivalves.

The cephalic expansions of the Clio are muscular, like those of the
Hyalcea, subserving locomotion, not respiration, as Cuvier believed.
The true branchial vascular network is developed in both Pteropods
upon the inner surface of the mantle. A heart, consisting of an au-
ricle and ventricle, is lodged in a pericardium, and situated on the
left side in front of the branchia, from which it receives the blood by
a large vein, and propels it by two aortas to the locomotive append-
ages and other parts of the head, and to the abdomen and its viscera.
The Hyalaea and Cleodora have no cephalic tentacles. The Cymbu-
lia has two small tentacula with an ocellus at the base of each.

* Eschricht, Anat. Unters. uber die Clione borealis. 4to. 1838.

GASTEROPODA. 293

The head of the Pneumodermon is characterised by two groups of
numerous tentacula, each terminated by a sucker ; and the recent re-
searches of Eschriclit* have brought to light an analogous structure in
the Clio, whose cephalic organs of prehension are much more complex
than Cuvier supposed. Each of the six conical retractile processes of
the head are perforated by numerous cavities, recognisable to the
naked eye as red points, but containing about twenty microscopic
pedunculated discs, the total number of which in the head of the
CliOi Eschricht estimates at 360,000 ! There are two slender and
simple tentacula which seem to exercise only the tactile faculty. Two
supra-cesophageal or cerebral ganglia are developed upon the upper
part of the nervous collar which incloses the beginning of the ali-
mentary canal; the two pedial and the two branchial ganglia are
closely approximated and connected with the inferior and lateral parts
of the nervous collar. From these centres the nerves are distributed
to all the viscera and parts of the body.

The male and female sexual organs are combined in the same in-
dividual. The duct of the voluminous testis communicates with a
spherical vesicula seminalis, and is then continued to the base of an
intromittent organ, which projects from an orifice on the right side of
the head ; this organ Cuvier compares in the Cymhulia to a small
proboscis ; in the Clio it is almost as long as the body, and proves
impregnation to take place by reciprocal coitus, as in many of the
inferior Gasteropods.

The ovarium is also a voluminous organ ; and the oviduct is wide,
and provided with glandular parietes through a great part of its
course ; it terminates close to the base of the intermittent organ.

The development of the ova of the Pteropoda has not yet been
observed.

Class Gasteropoda.

The transition from the Pteropoda to the present class is obviously
made by the Philliroe, the Glaucus^ the Carinaria^ and the Firola^
all floating pelagic genera remarkable for the delicacy of their tissues,
and the rudimental character of their gastric foot : these aberrant
Gasteropods manifest the same affinity to the preceding group by the
presence, in some, of lateral, symmetrical, more or less aliform ex-
pansions, and, in others, of a shell characterised by its elegant sym-
metry, lightness, and transparency ; that of the Carinaria much re-
sembles the shell of the Cymhulia in form, but is of a calcareous
texture.

* Loc. cit.
u 3

294 LECTURE XXII.

The typical Gasteropods, characterised by the greater development,
especially the breadth of their ventral muscular locomotive disc, con-
stitute a very extensive, and widely distributed class of Molluscous
animals, many of which appear to have superseded the extinct in-
habitants of the chambered shells in the organic economy of the ex-
isting shores. Most of the species are marine ; many inhabit fresh
waters ; a few are terrestrial. They offer corresponding conditions of
the respiratory organs in relation to these media, with minor modifi-
cations, of which systematic naturalists, and especially Cuvier, have
availed themselves,, in distributing the numerous and diversified mem-
bers of the class into orders.

In the lower organised Gasteropods the respiratory organs are ex-
posed ; those genera which support them on the back, or the sides of
the back, as the Glaucus, Eolida^ Tritonia, form the order Nudi-
branchiata, in which all the species are without shells, in the mature
state ; those genera which carry the gills at the lower part of the
sides of the body, between the foot and mantle, as the Phyllidia^
constitute the order Inferobranchiata : they are likewise naked or
shell-less. The genera in which the gills have a similar position, but
extend around the body, as the Patella and Chiton, form the order
Cyclobranchiata : they are defended by a conical shell composed of
one or many pieces.

In the rest of the class the respiratory organs are concealed. Those
genera, as the Aplasia and Bulla, which have the gills protected by
a fold of the mantle containing a rudimental shell, or by a reflected
process of the foot, form the order Tectibraiichiata. Those genera,
as Limax or Helix, which have a vascular air-sac or lung, protected
by a rudimental, or fully developed shell, form the order Pulmonata.
A small order of marine Gasteropods, including the Fissurella, and
Haliotis, which have their pectinated branchiae protected by a wide
shield-shaped shell, is called Scutibranchiata. Another small order,
in which similar branchiae are protected, with the entire body, by a
tubular shell, is called Tubulibranchiata.

In all the foregoing orders of Gasteropods the male and female
organs of generation are associated in the same individual ; in the
last and highest organised order, called Pectinibranchiata, the sexes
are distinct.

The soft parts of the Gasteropods are immediately invested by a
soft inarticulated lubricous integument called the mantle, in which
may be recognised an epidermal, a pigmental, and a dermal layer,
the latter being highly contractile. The shell results from the meta-
morphosis and calcification of cells deposited in layers beneath the
epidermis, in the situation of the rete-mucosum in the human integu-

GASTEROPODA. 295

ment. Its formation in the univalve Gasteropods commences in the
embryo, and the first-formed part is called the nucleus of the shell ;
the succeeding layers are not, however, formed around this, but are
added to the inner surface of the circumference of the previously
formed parts ; and the proportions in which the new formed layers
extend beyond their predecessors determine the figure of the future
shell. In some Gasteropods, at certain seasons, the margin of the
mantle in which the shell-forming processes have greatest activity
extends outwards at an obtuse or right angle to the last-formed mar-
gin of the shell, and after having formed a calcareous plate in this po-
sition, the mantle extends in the ordinary direction, increasing the
length of the shell, and is again similarly extended at a right angle
with the last formed part : it is to this periodical growth of the
mantle and plethoric condition of the calcifying vessels that the
ridges on the exterior of the shell in the wentletrap (^Scalaria
pretiosa) are due. Should the margin of the mantle, instead of
being uniformly extended, send outwards a number of detached
tentaculiform calcifying processes, these will form a row of spines
corresponding in length and thickness to the soft parts on which they
are moulded ; and, as the calcification of the processes proceeds, the
spines, which were at first hollow, become solidified, and finally sol-
dered to the margin of the shell. This development of pallial calci-
fying processes or filaments and of the resulting spines, likewise
alternates with periods of the ordinary increase of the shell ; and thus
its exterior surface may become bristled with rows of spines, as in the
Murex crassispina.

The most simple form of univalve shell is the cone, which may be
much depressed, as in the genus Umbrella, or extremely elevated and
contracted, as in the Dentalium, or of more ordinary proportions, as
in the Limpets. The apex of the cone is always oblique and ex-
centric ; directed in the Limpets towards the head, but in other Gas-
tropods towards the opposite extremity of the body. The conical
univalve shell is generally spirally convoluted, sometimes in the same
plane, as the Planorbis, but more usually in an oblique direction.

As a general rule the spiral univalve, if viewed in the position in
which its inhabitant would carry it if it were moving forwards from
the observer, is twisted from the apex downwards from left to right,
the spire being directed obliquely towards the right ; but in a few
genera, as in Clausilia, Physciy the shell is twisted in the opposite
direction, when it is called ' perverse ' or ' sinistra.l' Some species
of Bulinus, Partula, and Pupa, and a few marine shells, as Fusus
sinistrorsus, are sinistral. The part around which the spiral cone is
wound is termed the ' columella : ' this is sometimes simple, sometimes

u 4

^96 LECTURE xxir.

plicated : in some shells it is solid ; in some hollow ; in the latter case
its aperture is termed the ' umbilicus.'

The aperture which forms the base of the spiral univalve is bounded
by an ' outer lip ' and an ' inner lip,' which oflPers a smooth convex
surface, over which the foot of the Gastropod glides to reach the
ground. In many univalves the aperture of the shell is entire ; in
others, the margin is broken by a notch, or perforated by one or more
holes, or a portion of it is produced into a canal or siphon. These
modifications are important on account of the constancy of their re-
lation to certain conditions of the respiratory organs. Thus the
Pectinibranchiate Gastropods, in which the water is conducted to the
shell by a muscular tube or siphon, have the margin of the aperture
of the shell either notched or produced into a canal.

In some of the Gastropods the shell consists of one piece, when it
is termed an * inopercular univalve ; ' but the aperture of the shell
is in the majority of the species closed by a plate, attached to the
back of the foot, and called the ' operculum.' It is sometimes cal-
careous, forming a second shelly plate ; but it more frequently consists
of albuminous membrane only, or is horny ; thus presenting the con-
dition which the univalve shell itself manifests in certain genera, as
Limax and Aplysia. Some opercula increase by the addition of
matter to their entire circumference, and these are either concentric,
as in Paliidina, or excentric, as in Ampullaria and most of the Pecti-
nibranchiate Mollusks. Other opercula grow by the addition of matter
to part of their circumference ; and these are either spiral or imbri-
cated ; in the latter the layers of growth succeed each other in a
linear series. No operculum presents an annular form. As the
operculum sometimes varies in structure in species of the same genus,
as it is present in some volutes, cones, mitres, and olives, and absent
in other species of those genera, and as some genera in a natural
family, as Harpce and Dolium among the Buccinoids, are without an
operculum, whilst the other genera of the same family possess that
appendage, it obviously affords characters of very secondary import-
ance. In Lithedaphus ( Calyptrced) equestris the whole base of the
foot secretes a calcareous plate which is cemented to the rock, and
the shell appears to consist of two valves. In the Chiton the shell is
divided into many pieces arranged like scales upon the back.

Most univalve shells are composed of three strata, which differ in
the arrangement of the calcareous particles. Hunter* discovered
that the molluscous inhabitant of a shell had the power of absorbing
part of its dwelling. This property, which is now generally recog-

* Philos. Trans, 1785, p. 343.

GASTEROPODA. 297

iiised, is well illustrated by the thinning of the parietes of the internal
whorls of the Cones and Olives, from which two out of the three layers
of which they were originally composed may be observed to have
been removed. The absorption of shell is also illustrated by the re-
moval or smoothing down of the spines of the 3Iurices ; by the flat-
tening of the inner lip of the mouth of the Purpurce ; by the widen-
ing of the foecal aperture of the Fissurellce ; and it gives rise to
various other modifications in the form and structure of shell in the
progress of growth. Another change of form is due to the physical
decomposition or destruction of a part of a shell during the lifetime
of the inhabitant. This occurs to the apex of ceriain Univalves after
the shell has been evacuated by the original occupant in the widen-
ing and lengthening the shell to accommodate it to an increase of
bulk. Such shells are said to be " decollated," as, for example, the
Helix decollata.

The inhabitants of univalve shells dispose in different ways of that
part of their calcareous abode which they evacuate in the progress of
growth ; in the decollated shells the vacated spire is portioned off,
prior to its abrasion, by the formation of a thin nacreous plate. In
the Vermetus gigas the vacated portions of the tube are retained, and
successively portioned off, a series of concave plates or septa being
thus developed ; a similar structure is indicated in the remains of the
large elongated fossil shells, called Icthyosarcolites. In the Magilus
antiquus the posterior part of the shell, as the soft parts move for-
wards, is progressively filled up with a dense, solid, subtransparent,
crystalline deposit of carbonate of lime.

The part of the mantle which invests the viscera in the conchiferous
Gasteropods is smooth, thin, and sub-transparent, resembling the sac
of a hernia, which, with the viscera themselves, appears to have
escaped from the common muscular integument of the body. This
visceral mass, as it is termed, is lodged in the upper part of the cone
of the shell, the spiral turns of which it follows. The head and foot
of the animal can be protruded from the mouth of the shell, and be
retracted within its last whorl, by the action of a muscle, which has
its fixed point in the columella of the shell. The form and size of
this compartment of the shell, and of its aperture, correspond with,
and indicate the size of, the foot.

In the Pectinibranchiate Mollusca, which are the chief fabricators
of the beautiful turbinated shells of the conchological cabinet, the
foot is attached to the anterior part of the body by a narrow base ;
whence they have been termed by Lamarck Trachelipods.

These with the true Gasteropods are organised to subsist on a great
variety of food : they select both animal and vegetable matter in both

298 LECTURE XXII.

their living and decomposing states. The damage which the common
snail produces, by devouring the produce of the garden, is too well
known ; and, on the other hand, the common whelk preys upon its
congeners, nor do their strong shells defend them from its attacks.

The mouth is bounded by fleshy contractile lips in most of the
Gasteropods, and these are developed, in the Haliotis^ into a pair of
labial processes : it is likewise generally armed with horny plates,
trenchant or spiny, disposed either as jaws, or covering the tongue.
The upper lip in the snail is armed with a crescentic dentated horny
jaw, which is opposed by the bifid soft lip below. In the Tritonia, a
curved trenchant horny plate works vertically upon another of similar
form, and with these, as with a pair of curved scissors, this moUus-
cous animal crops the tough sea-weed which constitutes its food.
Certain fresh-water Gasteropods, as Limnceus and Planorhis^ combine
two lateral horny jaws with a superior dentated labial plate. The
Limpet rasps marine plants with a narrow horny plate or ribband beset
with numerous rows of minute recurved hooks, which armature ex-
tends beyond the mouth, and is longer than the entire body. The
whelk is provided with a more complicated instrument in the shape
of a proboscis, susceptible of considerable elongation, or of being
entirely concealed within the interior of the body. Its extremity is
vertically cleft, the divisions or lips having their inner surface beset
with recurved spines. In the interior of the muscular cylinder, there
is a tongue armed by a horny uncinated plate, as in the Limpets, but
of much less length : it is stretched upon two elongated cartilages,
which can recede from or approximate each other, or be moved together
to and fro, by special muscles : by these movements the spines can
be made to scrape with force against any opposed surface ; and it is
by the repetition of such movements, aided, as Cuvier conjectures,
by a solvent property of the saliva, that the whelk effects the per-
forations in the hard shells of other mollusca, upon the soft parts of
which it preys.

The salivary glands present different forms and degrees of develop-
ment in different Gasteropods, bearing the ordinary relations to the con-
struction of the mouth and the nature of the food. In the Calyptrcea
I found the salivary glands represented by two simple elongated se-
creting tubes. In the whelk they present a conglomerate structure,
are situated on each side the oesophagus, at the base of the proboscis,
along which they transmit their slender ducts to terminate on each
side the anterior spines of the tongue. In the Paludina vivipara
{Jig^ 121.), here selected for the illustration of the Gasteropodous type
of the molluscous organisation, the salivary glands are shown at v.
The proboscis, or muscular parietes of the mouth, is seen at /) in its

GASTEROPODA.

299

retracted state. The oesophagus 5' is long and slightly convoluted ; q'

is the last bend which the tube makes before expanding into the

121

Paludina vivipara.

Stomach, r : s, / show the folds of the intestine in the substance of the
liver and ovary ; it penetrates the branchial chamber at s^^, in which
the rectum, ty is seen passing along the base of the pectinated gills, g,
to terminate at i, close to the margin of the mantle f^ whicli forms
the branchial aperture. The letter a indicates the foot in its state of
contraction, when its inferior or ambulatory surface is bent trans-
versely upon itself : b shows the operculum attached to the posterior
part of the foot : c are the tentacula, with the attached ocelli : d is
the small siphon which projects below the right tentacle : n is the
heart, which consists, as in almost all Gasteropods, of a single auricle
and ventricle : h is the long and wide oviduct, w hich performs the
office of the uterus in this ovoviviparous species of Gasteropod : lis the
duct of a mucous or renal organ attached to the walls of the branchial
cavity.

The disposition of the viscera of other Gasteropods offers few im-
portant deviations from that in the Paludina vivipara ; but some of
the peculiarities in the structure of certain organs deserve special
mention.

In a few Gasteropods, the whelk, for example, the oesophagus pre-
sents a small ingluvial dilatation : the crop is wider in the AplysicB,
in which the coats of the second stomach, or gizzard {Jig. 122.), are

300

LECTURE XXII.

122

Stomach of Aplysia.

thickened, and the interior cal-
lous lining is beset with firm
horny processes, some in the
form of hooks or canine teeth,
others in that of rhomboidal
plates or molar teeth. These
complexities relate to the low
organised character of the food
of the AplysicB : the sea-weed on
which these Mollusca subsist,
after coarse mastication and com-
mixture with the salivary secre-
tions, is macerated in the crop,
conveyed to the stomach, there
pierced by the gastric spines,
percolated by the solvent juices, and pounded by the horny plates.
The chyme is then mixed in the duodenum(o) with the hepatic secre-
tion, and with the fluid, probably analogous to pancreatic juice, which
is secreted by a single long blind glandular sac (6), communicating
with the beginning of the intestine. A similar simple form of pancreas
is present in some species of Doris, and other fucivorous genera of
Gastropods, as Tritonia and Scyllcea, which likewise have horny gastric
teeth. In the Bidlcea aperta * the stomach is surrounded with three
large horny plates, concave externally and convex towards the cavity.
In the Bulla ligjiaria \ the gastric triturating plates are calcareous :
two of these plates present an irregular triangular form, with the
angles rounded off, slightly concave externally, and convex towards
the gastric cavity : they are united together by strong transverse
muscular fibres attached to their circumference, except at the upper
part of the gizzard, where a third valve of an oblong form is inter-
posed between the two lateral ones. The imposition of the name
Gioe7iia upon the large gastric plates of the Bulla, as the valves of a
new bivalve shell, will not soon be forgotten by conchologists.

In regard to the number of cavities, the most complex stomach in
the Gastropoda is that of the Onchidium, which has three longi-
tudinally plicated gastric compartments.

The intestine, after performing a few convolutions in the substance
of the liver and generative gland, always more numerous, and of
greater width in the herbivorous than in the carnivorous Gasteropods,
terminates, with a few exceptions, at or near the entry of the respi-
ratory cavity on the right side of the body. The anus has a median

Preps. Nos. 493, 494.

t Prep. No. 492.

aASTEROPODA. 301

position in the Doris and Testacella, and terminates on the left side
of the body in the Plahorbis.

The liver is a bulk}- gland, and is subdivided into numerous lobules
in all the Gasteropods : its secretion is derived from arterial blood,
and is usually poured by one or two ducts into the commencement
of the intestine. It is carried, however, into the stomach, and even
into the oesophagus, in the Onchidium : and the Haliotis not only
resembles the Palliobranchiata in the perforation of the stomach by
the bile-ducts, but likewise in the perforation of the ventricle of the
heart by the rectum, and in the division of the auricle into two
cavities.

The auricle is divided in the Fissurella and in the Chiton as in the
Haliotis. Both auricles, however, equally receive the oxygenated
blood from the respiratory organ^ as does the single auricle in all
the other Gasteropods. The ventricle propels the blood to the viscera
and muscular system of the body, and the heart is thus systemic, co-
ordinately with the condition of the muscular system and the general
endowments of the animal, as has been already explained in the
Introductory Lecture. * The aorta, continued from the apex of
the ventricle, divides into two principal branches in most of the
Gasteropods. The auriculo-ventricular aperture is usually defended
by two semilunar folds. The aorta, at its commencement, is fre-
quently strengthened and enlarged by a muscular layer, similar to
the bulbus arteriosus in fishes, and which, in the Aplysia, is continued
beyond the origins of the primary branches of the aorta. The large
venae cavse of the Aplysia are perforated by minute apertures, com-
municating with the cavity of the abdomen ; and the exterior of the
veins is provided with decussating muscular fibres, which probably
regulate the diameter of their peritoneal communications. Cuvier
supposes that this structure has relation to an absorption or passage
of fluid from the abdomen into the veins. The vessels conveying
the venous blood to the branchiae are continued from these veins
without the interposition of any muscular ventricle.

The general modifications of the respiratory organs are indicated
by the characters of the orders of the present class already defined.
In the terrestrial Gasteropods the breathing organ has the form of the
simple undivided vascular sac, like the lung in the lowest air-
breathing Vertebrate animals. The forms of the aquatic breathing
organ are as various as its position.

In most of the Nudibranchiate species the gills are tufted and rami-
fied, as in the higher Anellides ; they are penniform in the Haliotis,

* Page 6.

302 LECTURE XXII.

and pectinated in all the dioecious Gasteropods, as the name of their
order indicates ; in these they never exceed two in number, which
are of unequal size. In a few genera of amphibious Gasteropods a
pulmonary sac is combined with branchial organs. The branchial
surface is ciliated in all the Gasteropods, as is also the exterior surface
of the body in the small fresh-water species.

Besides the large and well developed hepatic and salivary glands
which are associated with the alimentary canal, we have seen that cer-
tain fucivorous Gasteropods present the simplest rudimental condition
of the pancreas. The situation of the follicular urinary gland and of
its excretory duct has already been pointed out in the Paludina
mvipara : in some species the duct dilates to form a small recep-
tacle. A group of follicular glands, sometimes imbedded in a distinct
glandular sac, is present in many species for the elimination of some
peculiar and characteristic colour; the yellow liquid of the BuUcb,
and the famous purple secretion of the Purpura, are products of
saccular modifications of this follicular gland. Numerous simple and
scattered follicular glands lubricate the mantle with its characteristic
mucus in all the Gasteropods.

At the grade of the Molluscous organisation which the Gasteropods
have reached, their capabilities and spheres of action become more
extended and diversified than in the Pteropods and Acephala ; some
are terrestrial, some arboreal, whilst the more numerous aquatic
species are endowed with power to attain, subdue, and devour organ-
ised matter, dead and living. The nervous system of the Gastero-
pods is accordingly not only more complex and concentrated, not
only subordinated to better developed masses in connection with
organs of special sense and exploration, but it offers greater variety
in its general arrangement and especially in the position of its gan-
glionSj than in the Lamellibranchiate class ; and with these modi-
fications considerable differences in the outward configuration of the
body are associated.

Some Gasteropods, for example, are symmetrical, more or less flat
or depressed ; others are compressed ; the majority are contorted and
lose their symmetrical form in an oblique twist : there are other di-
versities of organic structure which more immediately affect the con-
dition of the nervous system, for some species possess both eyes and
tentacles, whilst others are blind and akerous.

In the limpet (Patella), and in the Bulla, we find that the cerebral
ganglions, as in the bivalves, are still distant from each other, and
situated at the sides of the oesophagus, connected together by a
nervous chord or commissure which arches over that tube : from
these ganglions two filaments proceed backward on either side ; the

GASTEROPODA. 303

median and superior pair passes along the sides of the oesophagus, con-
verges and meets below to form a pair of ganglions in close contact
with one another which supply the foot and viscera : these are evi-
dently analogous to the bilobed pedial ganglion of the Mytilus. The
lateral and inferior filaments pass downwards to join two widely sepa-
rated branchial ganglions, analogous to those situated on the posterior
adductor in the Mytilus. We observe, however, a considerable dif-
ference in the relative positions of the pedial and branchial ganglions
in the limpet ; the latter have advanced into close contiguity with the
pedial ganglions, and are connected with them by the same transverse
chords, which in the Pecten and Mytilus serve merely to bring the
branchial ganglions themselves into mutual communication.

We thus observe in the lowest and least locomotive Gasteropods a
tendency in the nervous system to be aggregated at the fore-part of
the body, the cerebral ganglions rising more to the upper surface of
the now well-developed head, and the branchial and pedial ganglions
beginning to concentrate themselves about the mouth. But this
march of development does not prevent the homologies of the different
ganglia from being satisfactorily traced. In the limpet there is a dis-
tinct head and mouth, with organs of special sense ; and besides the
large antennal and small ophthalmic branches given off from the
cephalic ganglia, we find also superadded ganglia, having evident
relation to the muscular mouth and pharynx and to the complex
tongue, which are so many accessory parts appended to the simple
opening of the gullet, with which the alimentary canal commences in
the bivalves. The additional ganglia in question are placed below
the pharynx, and are brought into communication with the sentient
centres by a filament continued downwards and forwards from each
of these ganglia : they also inter-communicate by a loop which
forms a third azygos rudimentary ganglion beneath the oesophagus
completing an anterior ring corresponding to that which is formed by
the means of the pedial ganglion posteriorly.

The ganglions corresponding to the pedial pair in the Bullcea appear
not to be joined together by a transverse band, but to be connected
only with the branchial ganglion, and through them with the
cerebral ones. The three are placed so close together, that Cuvier
describes them as forming one mass. There are two pharyngeal
ganglia formed upon filaments descending from the cerebral ganglions.
The labial ganglions, which are devoloped in addition to the pedial
ganglions, originate from the latter in the Bulla lignaria, and are
connected with the cerebral ring only through them.

In the Haliotis^ the superior or oesophageal part of the oesophageal
circle is still a simple commissural chord. The sides of the circle are

304 LECTURE XXII.

formed by a double chord, which unite below in a single branchio
pedial ganglion; from which the visceral, as well as the branchial and
muscular, nerves radiate.

In the Doris and Onchidium the cerebral, pedial, and branchial
ganglions have coalesced into one annular mass, which, however, is
chiefly supra-oesophageal in its position, united below by a slender
chord passing across the under parts of the oesophagus. Two small
nerves are given off, which descend and form two small pharyngeal
ganglia, which, according to Cuvier, are united together. In the
Doris Solea the quadripartite character of this large mass is however
obvious.

In the Paludina vivipara the supra-oesophageal ganglions (^^. 121.
w, u) are distinct, and connected together by a transverse commis-
sural filament. The sub-oesophageal mass sends its principal branches
to the foot; but one nerve comes off from the right side, crosses the
oesophagus, and expands into a small ganglion Xy which distributes its
filaments to the retractor muscle that attaches the animal to its shell.

In the slug and snail the principal centres of the nervous system
are a supra-oesophageal and a sub-cesophageal mass ; but the complex
character of the latter and larger mass is indicated by the triple
nervous chord, which completes on each side the collar round the
alimentary tube. From the inferior mass the nerves radiate to the
muscular foot, the soft and susceptible integument, and the circulating
and respiratory organs. The upper ganglion receives the large nerves
of the tentacles and ocelli ; it also communicates on each side by two
minute filaments, proceeding from its posterior and outer angles, with
a small pair of stomato-gastric ganglions situated on the side of the
oesophagus.

The sub-oesophageal mass in the Limnceus stagnalis is of an
orange-colour, and consists of seven ganglions united together by a
loose cellular tissue.

In the Aplysia the sub-oesophageal ganglionic mass is divided
into two parts, which are joined together by a sub-oesophageal chord,
and brought into communication with the cerebral ganglions by ascend-
ing and converging chords. The cerebral ganglions are also joined
together above the oesophagus, and assume the position of a true
brain. They supply nerves to the tentacula, and give off anteriorly
two chords, which turn forwards to join below the mouth, where
they form a second oesophageal collar upon which the pharyngeal
ganglions are developed. The branchial ganglion is situated towards
the posterior part of the body; the connecting chords of this ganglion
join those of the pedial ganglia, but may be traced directly to the
brain.

GASTEROPODA. 305

The position of the cerebral ganglions varies according to the
degree of extensibility of the mouth and oesophagus. Thus, in the
Helix^ they are placed above the mouth ; in Carocolla, at the com-
mencement of the oesophagus ; in the Biiccinum or Whelk, low down
on the tube ; in the Purpura^ beneath the stomach.

As a general rule, we find that the superior ganglions give off
tentacular, ocular, and oral nerves, whilst the inferior masses are the
centres of the muscular, respiratory, and visceral internuntiate chords.
In the spiral pectinibranchiate univalves, where the .branchiae and
their nerves are twisted to the left side, it is the left branchia which
is atrophied, while the right one is of large size. The nerves are
similarly affected, the left one being filamentary ; whilst the right is a
large chord, and has the accessory branchial ganglion developed
upon it.

The principal oesophageal ganglionic circle is surrounded by a
thick membrane, which, in the large Tritons, assumes almost a carti-
laginous hardness. A coloured pigment is not unfrequently found
occupying a position analogous to that of the arachnoid, between
the dense outer membrane and the ganglions. In the Limnceus and
in the Planorbis this pigment gives to the ganglions their orange or
roseate hue.

Amongst all this diversity in the number, size, and position of the
nervous masses, certain ganglia are obviously analogous to those
which have received determinate names in the lamellibranchiate
Mollusca. The branchial ganglions receive impressions from^ and
transmit them to, the gills ; they communicate also with the brain, and
through that centre associate the gills with all other parts of the body.
The pedial ganglion is more commonly divided than in thebivalves, and
the two divisions are wider apart, in consequence of the great breadth
of the foot. In those Gasteropods which possess a naked muscular
mantle, we find a pallial ganglion associated with a pedial one, as in the
Aplysia. The cephalic ganglions assume the character of optic lobes
concurrently with the constancy and better development of the eyes ;
even when the organs of vision are more than usually minute or
wanting, the cephalic ganglions are always larger than in the
Acephala, and more decidedly superior in position. When separate,
they are united by a thicker communicating chord, and are larger in
proportion to the nerves given off from them. With the cephalic
ganglions, likewise, we find connected the labial and pharyngeal
ganglions, in which, perhaps, may reside the olfactory sense ; there
is good evidence, at least, that snails scent their food. The anterior
of the aggregated ganglions, which form the suboesophageal mass
in most Gasteropods, are in immediate connection with the acoustic

X

306 LECTURE XXII.

vesicles. The functions of the other ganglions of the body seem
to be limited to the automatic reception and reflection of stimuli.

Soft and lubricated and sensitive as the skin of the naked Mollusks
seems to be, there are not wanting reasons for supposing it to be
possessed of a very low degree of true sensibility. Baron Ferussac,
for example, states that he has seen the terrestrial Gasteropods, or
slugs, allow their skins to be eaten by others, and, in spite of large
wounds thus produced, show no sign of pain.

The vascular inferior surface of the foot can, doubtless, take cog-
nisance of the character of the surface over which it glides ; but the
special organs of the tactile sense are the tentacula or horns which
project from the lateral and upper parts of the head. These are
wanting in a few Gasteropods, hence called Akera : they are some-
times two, and never exceed four, in number in the present class In
the snails and slugs they can be retracted by an act of inversion.
The anterior is the normal or constant pair; the posterior pair,
which supports the eyes in the snail, is reduced to two short pro-
cesses, which extend from behind the basis of the anterior tentacula
in the Turho ; and which form slight projections from the outer side
of the base of those tentacula themselves in the Faludina (^Jig. 122.),
and in most Pectin ibranchiata. In the Aplysia, however, which has
four tentacula, the ocelli are sessile, and situated in advance of the
bases of the posterior pair.

The eyes never exceed two in number in the Encephalous Mol-
lusca : in the Gasteropods they present their largest relative size in
the Pectinibranchiata. In this preparation * from a large species of
Murex, you may readily discern the sclerotic tunic with its anterior
orifice, the expansion of the optic nerve posteriorly between the fibrous
and the pigmental tunic, and the large spherical crystalline lens,
covered anteriorly by the transparent corneal integument ; between
which and the lens, there is a very small interspace for the aqueous
humour and the pupillary circular opening left by the pigmental
layer or choroid.

The existence of the sense of hearing in the Gasteropods was
inferred by Dr. Grant, long before the organ was detected: he justly
concluded that the sounds emitted by the Tritonia arboresceiis under
water, were doubtless intended to be heard by others of the same
species. The very general existence of an acoustic apparatus under
its most simple conditions, in the lower Mollusca, has been esta-
blished by the discoveries of Siebold. It consists of two round
vesicles, containing fluid and crystalline or elliptical calcareous par-
ticles, or otolithes, remarkable for their oscillatory action in the living

* No. 1628.

GASTEROPODA. 307

or recently killed animals. In the Limnceus {fig. 123.), the acoustic

cells adhere to the posterior part of the
anterior ganglions of the great sub-
oesophageal mass {a, a)', e is the cap-
sule ; / the otolithes. They hold a
similar position in the snail and slug, in
which the number of otolithes ranges
from eighty to above a hundred. The
acoustic sacs are easily recognised by
"\ / submitting the head of the smaller

Limnffius sta^iis specics of Gastcropod, or of the young

of the larger species^ to a gentle com-
pression under the microscope.

From the analogy of the soft mucous skin of the Gasteropods to the
pituitary membrane of the nose, Cuvier was led to conjecture that
it might be the seat of the sense of smell ; but the analogy seems to
be too vague to render so general a diffusion of the nerves of a special
sense very probable. That the sense is possessed by these MoUusca,
is determined by the evidence which snails afford of scenting their
food.

The tongue is, in almost all the Gasteropods, a mechanical organ for
the attrition of the food : its complex horny uncinated armature seems
to unfit it for the delicate office of appreciating the sapid qualities
of nutritive substances ; but some sense of taste may be exercised
by the soft membranes of the pharynx.

Gasteropods have the power of repairing injuries and of reproducing
lost parts to a considerable extent. New tentacula soon grow to
replace those which may have been amputated. When they support
eyes, as in the snail, the organs of vision are also reproduced : the
mouth, with the horny jaw, has grown again in this Gasteropod ; and
when the snail has been decapitated, but with the oesophageal gan-
glions left behind, the head has been restored.

The general conditions of the sexual system have been already
briefly defined. The complexity and bulk of the combined organs in
the common slug and snail are truly extraordinary. The testis is the
small, compact, minutely follicular gland, imbedded in the substance
of the liver, and occupying, in the snail, the apex of the shell. The
vas deferens becomes closely attached to the oviduct in its course
towards the right side of the head, where it is joined by the short and
simple duct of a small prostatic sac in the slug, the corresponding sac
in the snail having a longer duct, from the middle of which a caecal
tube is developed. The vas deferens terminates near the base of a
very long and slender intromittent organ, usually retracted and con-

X 2

308 LECTURE XXII.

cealed within the visceral cavity, but which can be everted like the
finger of a glove and protruded externally.

The ovarium is a larger, more elongated, and less minutely granular
body than the testis, to which it is inferior or anterior in position.
The oviduct is long and wide, with thick glandular tunics, and, near
its termination, it communicates with the short and wide ducts of
two ramified tubular glands, called the ' multifid vesicles.' But the
complexity of the generative apparatus does not end here : the snail
is provided with a pyriform muscular sac, the aperture of which ter-
minates close to the generative outlet. The expanded base or head
of a slender conical calcareous style or dart is attached to the fundus
of the sac : its sharp apex extends close to the orifice, and by the
contraction of the sac it can be protruded outwards. With it the
snails pierce each other's skin, and the function of this curious organ
would seem to be to cause a preliminary excitement to the reciprocal
union of the two androgynous individuals.

In the dioecious Gasteropods the intromittent organ is usually of
extraordinary length : it is grooved in most, perforated in a few ;
capable of retraction in the Paludina, but doubled back upon the
outside of the mantle when drawn into the shell by the Biiccinum
and Strombus. In the Carinaria it is bifid.

The ova of the marine Gasteropods are enveloped, before exclusion,
in mucous capsules, prepared by a special gland situated near the
termination of the oviduct. The secretion in some species is soft,
flexible, and transparent; in most it hardens by contact with the
sea water, and assumes various definite and characteristic forms : the
nidus is sometimes simple, sometimes compound, but each compart-
ment contains many ova; and the development of the embryo pro-
ceeds in the nidamental chamber until its own little defensive shell is
acquired.

In the terrestrial Gasteropods the ova are usually spherical and
opake, and separately extruded. Snails and slugs oviposit in the
earth. The tropical Bulini * cement leaves of trees together to form
an artificial nest for their large eggs.

The ova of the sea.-s\ug (Trifo?iia) are expelled together in the
form of a long thread, and are arranged in a spiral manner in the
tenacious transparent covering of the thread. In the Doris muricata
the ova are aggregated in a flattened spirally disposed albuminous
band when excluded from the oviduct. The harder albuminous cap-
sules which defend the ova of other marine Gasteropods ofl^er a great
variety of forms, some of which are remarkable for their complexity,

* Prep. 2943. B.

GASTEROPODA. 309

others for their symmetry and beauty. Here are displayed the nida-
mental sacs of the frail Jantluna^\ they are of a flattened pyriform
shape, composed of a delicate reticulate film of albumen, and are at-
tached by one extremity to a float, formed likewise by a secretion of
albuminous matter, dilated into a group of cells filled with air. To
this float the parent Janthina commits her little progeny, and having
securely fastened their several cradles or nursery cells, she detaches
the float, which bears the ova to the surface, and sustains them where
they may best receive the full influence of solar light and heat. These
nidamental capsules of the Pyrula rapaf are attached in regular
linear series to portions of decayed wood ; they are of a flattened
sub-conical figure, adhere by their apex, and have their base emar-
ginate. The nidamental capsules of the whelk J are common objects
on our sea-shore ; they are aggregated in large irregular masses,
often attached to portions of oyster-shell ; each capsule presents a
depVessed ovoid figure, with one side convex, the other flat or concave.
The small nidamental cells of the Cowrey (Ci/prea) are aggregated
in a flattened group. In the Turbinella^ the cells are of a flattened
sub-pentagonal form, and adhere together, superimposed one upon
the other, forming what is termed a camerated nidus. Each chamber
contains between twenty and thirty embryos. In this preparation
you may observe that the rudimental shell is completely calcified and
fitted to defend the little Gasteropod before it emerges from the tem-
porary shelter provided for it by the parent. Numerous other modi-
fications of these secreted nests of the Gasteropodous MoUusca might
be enumerated.

The general course of development of the Mollusca of the present
class has been observed in the Planorbis by M. Jacquemin, and in
the LimncBus by M. Dumortier. The transparency of the mucous
capsules of the ova and of the ova themselves in these fresh-water
Gasteropods renders them favourable subjects for such observations.
The development of marine Gasteropods has been traced by M. Sars
in the Tritoiiia, Doris, and Aplysia, and has been likewise studied
in the latter genus, by Dr. Van Beneden.

In all these Mollusca the first steps in the formation of the embryo,
after the disappearance or metamorphosis of the germinal vesicle,
are the multiplication of the cells of the vitellus producing the
twofold, fourfold, and more numerous subdivisions, like those which
have been observed in the ova of so many of the foregoing classes.
The leading differences in the Gasteropods at this stage of develop-

* See Preps. 2945, 2946. f See Prep. 2947. A.

\ Preps. 2948, 2949. § Prep. 2950.

X 3

310 LECTURE XXII.

ment depend upon the aggregation of the fissiparous cellules around
one or around several centres ; whereby, since all subsequent deve-
lopment radiates from such centres, one or many embryos may be
matured in the same ovum. Thus the ovum of the Tritonia may give
issue to seven or eight embryos ; whilst that of the Planorbis and of
most other Gasteropods is the seat of development of a single young one.
In the Planorbis the single centre of the ovum, or the germinal
vesicle with its nucleus, is very evident in the ovarian ovum. The
metamorphoses, which lead to the disappearance of the vesicle^ take
place in the oviducal pouch called the ' matrix.' The transparent nida-
mentum in which the ova are excluded is shield-shaped and striated ; it
is not attached to any foreign body but falls to the bottom. After the
usual subdivisions of the yolk, a group of less opake cells makes its
appearance in a particular part of the periphery of the granular mass ;
and an epithelial membrane begins to spread over its surface, from which
cilia are soon developed. Their action begins about the third day to
affect the surrounding albumen, and afterwards to rotate the yolk
itself. The aggregation of stronger and more numerous cilia on a
particular part of the surface of the yolk indicates the seat of the de-
velopment of the respiratory organs. Two groups of extremely
minute and compact cells, covered by a thicker epithelium, project
from two other parts of the surface, and constitute the rudiments of the
head and foot. The centre of the yolk presents the form of larger
and less regular globules, which indicate the position of the wide
digestive sac. The rudiments of the head and foot are sufficiently
obvious on the fifth or sixth day ; the respiratory organs are formed
on the sixth or eighth day, according to the warmth of the weather.
On the eighth day the characteristic tentacles begin to sprout from
the rudimental head. On the tenth day all that part of the vitellus
or embryo M^hich is not occupied by the head, the foot, and the
breathing organ, is covered by a thin and transparent pellicle, which
is the rudiment of the shell. On the eleventh day one of the large
central globules of the yolk begins to distinguish itself from the ali-
mentary mass by feeble contractions and dilatations, of which about
sixty may be counted in a minute : this is the heart. The mouth can
now be discerned, and the small eyespecks appear like black granules
at the base of the tentacula. On the twelfth day the embryo moves
by its own contractions independently of the rotation produced by the
cilia. On the thirteenth day acts of deglutition are discernible ; the
embryo swallows the remaining albumen, the anus is completed, and
the genital organs begin to be formed. On the fourteenth day the
young Planorbis ruptures by more violent contractions the chorion,
and escapes into the water, protected by its own flexible shell.

GASTEROPODA. 311

In the Physa, the nidamental mass is short and ovate : in the
LimiKBus it is oblong, and not striated, as in the Planorbis. The
double movement of the embryo is more conspicuous in the LimncBus
than in the Plajiorbis. The first movement of the yolk is one of
rotation upon its axis ; but, as development proceeds and the ciliary
vibrations are strengthened, the embryo begins to travel in an ellip-
tical course around the interior of the e^^ ; its two movements (to
compare small things with great) resembling those of the planets in
the solar system.

The ova of the Aplysia are excluded in a long string, enveloped
by a transparent flexible mucus, the ova being aggregated in several
irregular series in its centre. When examined at this period, tlie
yolk has apparently divided itself into six, seven, or more numerous
globules ; or_, in other words, as many germinal vesicles included in
the same mass of albumen and in a common chorionic coat, have
given origin to as many aggregations of vitelline cells ; these, therefore,
may be regarded as so many independent yolks^ in each of which the
same progressive fissiparous multiplications have been observed, as
in the single vitellus of the ovum of the Planorbis, and of animals in
124 125 general. Fig, 124. exhibits one of these yolklets

C^^ prior to the commencement of the fissiparous
\jj\ action, by which subdivision of the mass is pro-
Apiysia. " duced. Fig. 125. shows the quadrifid product of
that action and of the assimilative powders of the resulting divisions
A small clear vesicle, probably the seat of further subdivisions, is
specially indicated by M. Van Beneden at a.

In Jig. 126. the multiplication of the globules has increased, and
126 127 two of them, of larger size than the rest,

indicate, one, the seat of the future branchial
organs, the other that of the muscular mass.
The ciliated epithelium, with which the
vitellus is now almost entirely covered, oc-
casions the usual rotations of that body.
The progress of transformation of this monad-like embryo to the Gas-
teropodous form, resembles closely that which has been described in
the Planorbis. The remains of the vitelline msiss (Jig. 127. a), not
yet metamorphosed into special organs, indicates the expanded
alimentary sac; b is the apex of the rudimental foot, and c the
coarsely ciliated surface, which constitutes the now external branchia.
These parts protrude from a rudimental, thin, pellucid and flexible
shell, which covers all the rest of the surface of the body. The
arrows indicate the direction of the rotatory movements of the embryo,
which now likewise describes its elliptical revolutions in the chorionic

x 4

312 LECTURE XXIII.

cavity. As development proceeds and the embryo increases in size,
the shell acquires a more distinctly turbinated form, and is slightly
bent out of its vertical plane (^^7. 128.).
An operculum (e) is now observed to be
formed upon the protruded surface of the
foot; the oesophageal ganglion is visible at
d. The ciliated branchial surface (c) begins
to be withdrawn more into the interior;
and, in this state, protected completely by
an external shell, the young Aplysia is
^v^y^^^- launched into the ocean.

Truly may the subsequent growth, which effects an entirely internal
position of the shell, with such a mutation of its form that the primi-
tive nucleus can scarcely be detected upon the almost flattened plate
now destined to protect the equally internal respiratory organs of the
mature animal, justify us in applying to it the term metamorphosis.
This term is still more applicable to the developmental phenomena
in the Tritonia and Doris ; since these Gasteropods, which are not
only naked, like the Aplysia, but devoid of any internal rudiment of
a shell, are provided with a delicate little nautiloid horny external
shell in their young state.

LECTURE XXIII.

CEPHALOPODA.

We trace the progressive diminution of the existing species of Gas-
teropodous Mollusca by their fossil shells through the descending
strata of the tertiary periods of geology, beyond which such indi-
cations become very doubtful and obscure.* In the oldest tertiary
deposits, not more than ^\ per cent, of the remains of any class of
Mollusca have been identified with species now living. From this
striking fact, which Mr. Lyell looks upon as indicating the dawn of
the existing state of the testaceous fanna, he has proposed the term
' eocene ' for these strata. In the next, or ' miocene ' tertiary
period, there are about 17 per cent, of fossil shells, identical with

* The supposed recent species of Trochus observed by Defrance in chalk, and
the Paludina and Cyclas, described by Dr. Fitton from the Wealden, are not con-
sidered to be identical with existing species by Deshayes and Lyell.

CEPHALOPODA. 313

recent species; in the deposits of a third or newer era (pliocene),
from 35 to 40 per cent., and, in still more modern formations
(pleistocene), the primitive forms have almost disappeared, and the
number of species identical with those now living is from 90 to 95
per cent.

Amongst the shells which characterise the eocene strata, there
appear four or five of symmetrical figure, divided into chambers,
which are perforated by a tube or siphon, like this large Nautilus
and this little Spirula, but belong to species which are unknown
in modern seas. In the secondary formations, which succeed the
eocene in depth and order of antiquity, the chambered siphoniferous
shells become more numerous and diversified ; they depart further
from the two remaining recent types, and manifest a rich variety of
form and structure. From these modifications of the shells we not
only infer corresponding differences in the habits of their extinct
occupants, but we can trace, in some instances, the nature of the
associated differences in the organisation of the perishable soft parts.

The vast number of the complex shells known by the names of
Ammonites, Orthoceratites, Hamites, Baculites, Turrilites, Belem-
nites, &c. ; and the constancy which particular genera and species
manifest in their relations to particular strata, indicate that the
functions which their molluscous fabricators performed in the organic
economy of the ancient world must have been equal and closely
analogous to those which have since been assigned to the Pectini-
branchiate Gasteropods, that have superseded them in the seas of the
tertiary and existing epochs.

What, then, were the nature and affinities of the extinct con-
structors of those ancient chambered siphoniferous shells ? Earnestly
and repeatedly had this question been pressed upon the attention of
zoologists and comparative anatomists, and long was it before any
satisfactory reply could be returned. The Nautilus Pompilius and
Spirula australis, which represent in the existing seas that vast
assemblage of siphoniferous Mollusca which peopled the ocean
during the secondary epochs, could alone yield the requisite data for
its determination, and for a long period comparative anatomists were
disappointed in their demands for these most rare and coveted sub-
jects. In fact, until the year 1832, geologists could be supplied only
with conclusions based upon more or less probable analogies and
conjectures. Before this period, only one account of the Nautilus
Pompilius was extant, in the work of Rumphius, a Dutch naturalist
of the 17th century, whose figure of the animal was pronounced by
Cuvier, the profoundest malacologist of his age, to be ' indechiffrable.'
The little light that it might have thrown upon the interesting

314 LECTURE XXIII.

question of the affinities of the Nautilus was obscured by the gro-
tesque, and, as they have since proved to be, fictitious figures of the
animal, subsequently published by De Montfort and Dr. Shaw, and
the evidence of Rumphius seems to have been rejected by the natural-
ists of the French circumnavigatory expedition under Captain Freycinet,
who, on their return in 1831, published a description and figures of part
of an unknown molluscous animal, presumed to be that of the Nautilus
Pompilius ; and which, had their conjecture been verified, would have
indicated the chambered shell of the Nautilus to have been an ap-
pendage to some huge Gasteropod, allied to the Carinaria.

If the claims of the Ammonite and its extinct congeners to take
rank in a higher class of Mollusca, had appeared to some zoologists
to be established by the figure of the animal of the Spirula, pub-
lished by Peron, it might, at the period to which I allude, have
been objected that this evidence, likewise, had been invalidated by
Fremenville's assertion to Brongniart, cited by De Blainville *, that
the animal of the Spirula was wholly different from Peron's descrip-
tion of it.

If an appeal had been made from the unsatisfactory and conflicting
evidence derivable from the existing chambered siphoniferous shells
to the simple univalve of the Argonauta, which resembles them in its
symmetrical figure, it might, on the one hand, have been objected that
the correspondence of outward form alone, without the camerated and
siphonated structure, was insufficient to support the conclusion of the
cephalopodic nature of the Nautilus or Spirula, since the shell of the
Carinaria might have been adduced as much more closely resembling
that of the Argonauta ; and, on the other hand, the scepticism of the
majority of conchologists as to the Argonaut shell being actually
fabricated by the Cephalopod usually found in it, might, until a very
recent period, have been adduced to show how little value could be
attached to the superficial resemblance between the Argonaut shell,
and that of the Nautilus, in the determination of the Cephalopodic
character of the constructor of the latter ; and, by inference, of those
of the allied extinct chambered shells. Most acceptable, therefore,
at this conjuncture, was the arrival of the molluscous inhabitant of the
Nautilus Pompilius, and a just subject of congratulation to us when
we reflect on the share which this College has had in supplying the
much wanted information.

The long-sought-for animal was captured in the South Seas by
Mr. George Bennett, a member of the College, and by him presented

* Malacologie, t. i. p. 381., 8vo. 1825. Nouvelles Annales du Museum, t. iii.
p. 20. 4to 1834.

CEPHALOPODA.

315

to the museum : here it was anatomised, and the description with
copious and beautful illustrations published by the Council.*

The dissection of this unique specimen established the claims of the
Nautilus Pompilius to rank in the highest class of Mollusca, and at
the same time brought to light so many important modifications in
the cephalopodic type of structure as to necessitate the establishment
of a new order for its reception. I propose to devote the present
Lecture to the demonstration of the principal organic characters of
this order, which I have called Tetrabra?ichiata, and to a brief review
of the extinct chambered siphoniferous shells, and of their relations
to the existing Cephalopoda.

The soft parts of the pearly Nautilus (Jiff. 129.) form an oblong

Nautilus Pompilius.

mass divided by an irregular transverse constriction into two nearly
equal segments ; the posterior is smoothly rounded, soft, and membra-
nous, containing the viscera, and adapted to the last chamber of the
shell ; the anterior is densely muscular, and includes the organs of
sense and locomotion.

The mantle is very thin upon the posterior part of the body ; it is
continued backwards in the form of a slender tube, which penetrates
the calcareous siphon (c), in the septum closing the occupied chamber
behind, and is thence continued, as the membranous siphon (c?),
through all the other divisions of the shell to the central nucleus. As
the mantle advances tow^ards the anterior part of the abdomen, it in-
creases in thickness, becomes more muscular, and extends freely out-

* Memoir on the Pearly Nautilus, 4to. 1832.

316 LECTURE XXIII.

wards, forming a wide concave fold in the dorsal aspect (e), which is
reflected over the black-stained involuted convexity of the shell. The
margin or collar of the mantle is continued downwards and forwards
on each side with a sinuous outline, and is perforated below for the
passage of the muscular expiratory and excretory tube called the
funnel (i). Besides the muscularity of the free border of the mantle,
which indicates its power of extension and contraction, its surface is
studded with the orifices of many minute glandular crypts ; and it is
the organ by which the growth of the shell is principally effected.
The nidamental glands form two circular convexities on the ventral
surface of the abdomen, behind which the mantle is encircled by a
thin layer of brown matter, like the periostracum, which is very nar-
row above and below, but expands on each side into a broad plate,
corresponding in size and form with the surfaces of attachment of the
two great muscles for adhesion to the shell.

The anterior or muscular division of the Nautilus, which may be
termed the head, forms a strong and wide sheath, containing the
mouth and its more immediate appendages ; its inner surface is for
the most part smooth, the outer one divided and extended into many
parts or processes. The chief of these forms a broad triangular mus-
cular plate or hood (/), covering the upper part of the head, and
presenting a middle and two lateral superficies ; the former being
traversed by a median longitudinal furrow, indicating the place of
confluence of the two large hollow tentaculiferous processes of which it
is composed. The back part of the hood is excavated for the lodge-
ment of the involuted convexity of the shell, and the above- described
fold of the mantle covering it. Each side of the head supports a
group of perforated processes or digitations, the largest of which is
next the hood, and the rest decrease in size as they descend in posi-
tion. Exclusive of the short subocular_, perforated process *, the digi-
tations are eighteen in number on each side disposed irregularly, but
all directed forwards, some not reaching as far as the anterior margin
of the head, others projecting a few lines beyond it. They are of a
conical, subtriedral form : the large one next the confluent pair which
forms the hood, has, like that part, a papillose outer surface. Each
process contains a long and finely annulated tentacle (g), of a sub-
triedral form, with the inner surface incised, as it were, by deeper and
fewer cuts {^fy- 132. e), so as to present the appearance of a number of
close set transverse plates, slightly indented by a median longitudinal
impression (Jiff- 132./). This modification must increase the prehen-
sile and sentient properties of the inner surface of the tentacle, and it is

* Particularly described and shown not to be tentaculiferous by M.Valenciennes,
Nouvelles Recherches sur le Nautile Flambe, Archives du Museum, 4to. 1839.

CEPHALOPODA. 317

on the corresponding part of the larger and fewer tentacles of the
dibranchiate cephalopods that the acetabula are developed. The
angle between the two outer finely annulated surfaces subsides near
the end of the tentacle, which thus becomes flattened.

To the nineteen tentacula which are supported by the confluent
and free digitations on each side of the head, two others must be
added, which project from very short sheaths, one before, the other
behind, the eye ; the lateral transverse incisions are deeper in these
than in the digital tentacles. The eyes are about the size of hazel
nuts, and are attached each by a short peduncle to the side of the
head, behind the digitations, and a little below the margin of the
hood. The inferior surface of the oral sheath is excavated for the
lodgement of the infundibulum.

The mouth is armed with two mandibles, shaped, as in other
cephalopods, like the beak of a parrot reversed, the lower mandible
i^fig' 129, I) overlapping and curving upwards beyond the upper
one iji). Both mandibles are horny, with their tips encased by dense
calcareous matter, and their base implanted in the thick muscular pa-
rietes of the mouth.

They are immediately surrounded by a circular fleshy lip with a
plicated anterior border, external to which there are four broad flat-
tened processes continued forwards from the inner surface of the oral
sheath, two of which are superior, posterior, and external, the other
two ill) are inferior, anterior, and more immediately embracing the
mouth : the latter are connected together along their inferior margins
by a middle lobe, the inner surface of which supports a series of
longitudinal lamellae. On the inner surface of the oral sheath beneath
these processes there are two clusters of soft conical papillae, and on
each side of these a group of lamella?. Each of the four processes,
which I have called ' labial/ is pierced by twelve canals, the orifices
of which project in the form of short tubular processes from the an-
terior margin, and each canal contains a tentacle similar to, but some-
what smaller than those of, the digitations. Thus the number of tenta-
cula with which the pearly Nautilus is provided, amounts to not less than
ninety, of which thirty-eight may be termed digital;, four ophthalmic,
and forty-eight labial. In the second specimen of this rare molluscous
animal, presented to the college by Captain Sir Edward Belcher,
there was a slight diff'erence in number in the digital tentacula
of the two sides, nineteen being on the right, and seventeen on the
left side. The labial processes in the specimen of Nautilus described
by M. Valenciennes contained thirteen tentacles instead of twelve; and
some slight variation is not surprising in the number of prehensile
organs developed in such unwonted profusion in the Nautilus.

318 LECTURE XXIIl.

The skeleton of the Nautilus consists of two parts, equally distinct
in their position, texture, and organic properties : the one is the
external chambered shell; the other is a rudimental cartilaginous
cranium, which sends out processes for the attachment of the prin-
cipal muscular masses. The shell of the Nautilus consists of an
elongated sub-compressed cone, convoluted in close spiral whorls,
upon the same plane, so as to be perfectly symmetrical. In the full-
grown mollusk, three fourths of the shell from the commencement no
longer serve to lodge the animal, but have been partitioned off, as
they have been progressively evacuated, into a number of chambers
(yfig^ 129. 5, 6), increasing regularly and gradually in size from the
first to the last, or to the last but one. The open chamber («, a),
which contains the animal, is much larger than the rest, slightly
curved, rounded behind and on the ventral aspect, and divided into
two concavities on the dorsal aspect, by the projecting involuted
spire. On the anterior surface may be observed two slight impressions
of the large lateral muscles, and that of the connecting narrow cincture,
and, posteriorly, the infundibular aperture of the calcareous siphon
is seen at the middle of the last septum. This calcareous tube extends
about one fourth of the way towards the succeeding septum, which,
with all the others, is similarly perforated and prolonged backwards
near their middle part. The septa, about thirty-five in number, are
concave towards the aperture of the shell, except below, where they
are convex transversely ; for their circumference does not follow
precisely the internal surface of the spiral cone, but describes a
slightly sinuous outline. The shell consists of two layers ; the outer
one opake, white, or stained with the characteristic red- brown stripes ;
the internal layer is twice as thick as the former, and of a nacreous
structure and aspect : the external surface of the shell is naturally
covered with a reddish brown or greenish epiderm or periostracum ;
and upon the involuted convexity of the shell, the dorsal fold of the
mantle deposits a thin plate of a vitreous texture, stained externally of
a deep black colour, which can be traced as an extremely thin ad-
ditional layer along the interior whorls of the shell. In the Nautilus
Pompilius the hole or umbilicus, at the extremities of the imaginary
axis round which the involutions of the shell have been made, is
filled up by the deposition of the semi-vitreous material : but in the
species or variety termed Nautilus umbilicatus, the margins of the
dorsal fold of the mantle are not developed to the same extent, and
the umbilicus continues open. The septa consist exclusively of the
nacreous substance : they are thinnest at their margins, which, from
their oblique applications to the wall of the shell, increase its thick-
ness at the line of contact. The chambers are lined by a thin mem-

CEPHALOPODA. 319

branous pellicle, thrown off by the mantle when the animal was in
the act of advancing forwards to enlarge its shell and form a new
septum.

The internal cartilaginous skeleton of the Nautilus is confined
to the inferior surface of the head : no part of it extends above
the oesophagus. Viewed sideways, it presents a triangular form ; a
portion of the annular brain is protected by a groove on the upper
surface of the cartilage : two strong processes are continued from its
anterior and superior angles into the crura of the infundibulum,
giving origin to the chief muscles of that part. Two other thinner
processes are continued backwards, and curve inwards and down-
wards : they give origin to the two great muscles which pass from
the internal to the external skeleton, or, in other words, attach the
animal to the shell.

The muscular fibres of the head or oral sheath arise from the
whole of the anterior or outer part of the internal skeleton. The
muscular structure of the funnel presents a much greater develop-
ment than in the naked Cephalopods ; and, from its relation to those
masses which, on the one hand, attach the soft parts to the shell, and,
on the other, connect the head to the body, we may conclude that
the funnel is the principal organ of natation^ and that the Nautilus is
propelled, like the Octopus, by a succession of jerks occasioned by
the reaction of the respiratory currents upon the surrounding water.
The orifice of the funnel is guarded by a valve {fig. 129. i^).

The retraction of the tentacula is done by longitudinal fibres, the
elongation by transverse ones. These are not, however, disposed in
circular or spiral series, so as to attenuate and lengthen the tentacle
by a general compression, but present a more complex and beautiful
disposition by w^hich they diminish the transverse diameter without
compressing the central nerve. The transverse fibres {fig. 1^2. a)
arise in numerous and distinct fasciculi from the dense cellular tissue
(fig. 132. b), surrounding the nerve in the centre of the tentacle
(fig. 132. d), and radiate at equal distances to the circumference; they
divide and subdivide as they diverge, and also send off lateral fibres,
which form a delicate network in the interspaces of the rays, especially
at the angles : the meshes include the longitudinal fasciculi, the cut
ends of which are shown at c, fy. 132.

The mechanical arrangement of the contractile fibres is very similar
to that of the complex muscles described by Cuvier in the proboscis
of the elephant. The attenuation and elongation of this brobdigna-
gian tentacle must be effected without compressing the central
breathing tubes, and transverse fibres accordingly radiate from the
dense ligamentous tissue which surrounds them : the same prospective

320

LECTURE XXIII.

contrivance is manifested to prevent the compression of the nerves
and vessels in the muscular system of the ninety proboscides of the
Nautilus.

For the special account of the myology of the Nautilus, which
includes the muscles of the oral sheath and its digitations, those
of the labial processes and mouth, those of the infundibulum, those
for adhesion to the shell, those of the mantle, those of the tongue,
the fibres of the tunic inclosing the liver and stomach, and the
muscles of the organic system, I must refer to the published mono-
graphs on the anatomy of this animal.*

The principal masses of the nervous system of the Pearly Nautilus
{fig* 130.) are concentrated in the head. The supra-oesophageal

part, or brain (a), presents the form
of a short, thick, transverse, round
chord or commissure, connected at
each extremity with three gangli-
onic masses. The middle and supe-
perior of these {h) supplies the eye
and the inferior hollow tentaculiform
organ : the anterior and inferior
ganglion (c) meets its fellow below
the oesophagus ; the posterior gan-
glion {d), in like manner, joins that
of the opposite side and forms a
second and posterior oesophageal
ring. The nerves given off imme-
diately from the supra-oesophageal
mass supply the muscular and other
parts of the mouth, and have small
pharyngeal ganglions developed up-
on them. The anterior oesopha-
geal ring gives off principally the
nerves to the tentacula (/,/), and
the two median ones (^) are con-
nected with a ganglion (/^), which
supplies the tentacula of the inferior
labial processes and the lamellated
Nervous System. Nautilus. organs on that part of the Oral

sheath. The tentacular nerves are continued, like those of the arms
in the higher Cephalopods, along the middle of the tentacle, at-

* Memoir on the Pearly Nautilus.
Museum d'Histoire Naturelle. 1839.

4 to. 1832. Valenciennes, Archives du

CEPHALOPODA. 321

tached by loose cellular tissue to the vessels of the part. The pos-
terior collar gives off numerous nerves (m) of a flattened form,
which supply the muscles of the shell. The respiratory nerves
form a small ganglion (q) at the base of each pair of gills, from
which branches are sent to those organs, to the heart, and to the
appendages of the veins. A plexus of more delicate visceral nerves
(r) is continued backward along the interspace of the branchial
nerves, and the chief branches are connected with a small ganglion
situated between the cardiac and pyloric orifices of the stomach. The
posterior subcesophageal nervous mass combines the analogues of both
the branchial and pedial ganglions in the inferior Mollusca : the an-
terior ring answers to the ganglia in the higher Cephalopods, called
' pes anserinus ' by Cuvier : the ophthalmic tentacula, which derive
their nerves (71, n) close to the origin of the optic ganglion, may be con-
sidered as analogous to the four tentacula in the Aplysia. The hollow
plicated process beneath the eye, which Valenciennes regards as the
olfactory organ, likewise receives its nerves from the extremity of
the supra-cesophageal chord. Three small nervous filaments, de-
scribed by the same author as passing from the extremity of the
supra-oesophageal chord to the adjoining part of the cephalic cartilage,
he considers as acoustic nerves ; but these nerves are given off from
the sub-oesophageal ganglion in the higher Cephalopods, and in all
the Gasteropods, in which the organ of hearing has been observed.

The eyes, as before stated, are attached each by a short pedicle to
the side of the head, over-arched by the projecting margin of the hood.
The form of the ball is sub-hemispherical, being flattened anteriorly
along its inferior border, there is a slightly elevated ridge, from which
a smaller ridge is continued to the middle of the anterior surface of
the eye, which is perforated by a round pupillary aperture, about a
line in diameter. The sclerotic tunic, which is a tough, ligamentous
membrane, is thickest posteriorly, and becomes gradually thinner to
the margin of the pupil. The optic filaments form a pulpy mass at
the floor of the eye, from which the retinal expansion is continued as
far forwards as the semidiameter of the globe : it is lined, like the
rest of the interior of the eye, by a thick black pigment, which is
doubtless perforated by the retinal papillae, or otherwise a perception
of light must take place in a manner incompatible with our know-
ledge of the ordinary mode in which the retina is effected by lumi-
nous rays. The crystalline lens would seem to be small, if it exists
independently of the vitreous humour : it was not present in the speci-
men dissected by me, and M. Valenciennes states that he was unable
to observe any of the humours of the eye.*

* Loc. cit., p. 289.
Y

322

LECTURE XXIII.

The cavity in the cephalic cartilage, apparently that described in
my Memoir * as containing a sinus of the cephalic veins, but which
M. Valenciennes regards as the organ of hearing, is defective in the
structures which the uniform analogy of that organ in the molluscous
subkingdom leads us to conclude are essential to it : there were no
traces, for example, of otolithes.f This militates more strongly against
the idea of the French anatomist than even the place of origin and
anomalous number of the minute nervous filaments which he describes
as penetrating the cavity in question.

With respect to the organ of smell, most physiologists will, I
think, admit that the structure and position of the soft close-set
membranous lamellae at the lower and inner part of the oral sheath
immediately in front of the mouth, manifest the conditions of the
olfactory organ more fully and naturally than do those short hollow
tentacles which project from the outside of the head beneath the eyes.
The complex and well developed tongue of the pearly Nautilus
exhibits in the papillae of its anterior lobes and in the soft ridges of
its root, the requisite structure for appreciating the quality of taste.

The papillae upon the exterior surface of the two large confluent
digital processes forming the hood and of the two digitations next in
size immediately beneath them, form a remarkable character in the
Nautilus, on account of their obvious similarity to tactile papillae ;

but the sense of touch must be
specially exercised by the nu-
merous cephalic tentacles, which,
from their softness of texture, and
especially their laminated inner
surface {fig- 131. /), are to be
regarded as organs of exploration
not less than as instruments of
prehension.
Section of tentacle, Nautilus. The calcareous extremity of the

upper mandible is sharp-pointed and solid to the extent of five lines.
The lower mandible is sheathed with a thinner layer of the hard
white substance, which forms a dentated margin. The fossils termed
« rhyncholites,' are the analogues of these calcareous extremities of
the beak in cognate extinct cephalopods. The muscular subspherical
mass, which supports and moves the mandibles, is provided with four
retractors, and can be protruded by a strong semicircular muscle,
which is continued from the margin of one of the inferior labial

i3i

* On the Pearly Nautilus, 4to, 1832, p. 16.

f '« Elle etait remplie d'une pulpe homogene " (coagulated blood?), " et ne con-
tenait aucune sorte de concretions." — Loc. cit., p. 291.

CEPHALOPODA. 323

processes over the mandibles and their retractor muscles to the labial
process of the opposite side.

The tongue is supported by a horny, slightly curved, and transversely
striated plate. The fleshy substance of the tongue forms three dis-
tinct papillose caruncles anteriorly, into which the retractor muscles
are inserted. The dorsum of the tongue is incased by a thin layer
of horny matter, supporting four longitudinal rows of recurved spines;
behind which the surface is again soft and papillose. Two broad
duplicatures of mucous membrane project forwards from the sides of
the pharynx; they each include a simple layer of salivary follicles, the
secretion of which escapes by a single perforation in the middle of
the process.

The lining membrane of the pharynx is disposed in numerous
longitudinal folds, w^here it begins to contract into the oeso-
phagus. This tube, having passed through the nervous collar, dilates
into a capacious crop, from the bottom of which a contracted canal,
half an inch in length, is continued to an oval gizzard. The intestine
commences near the cardiac orifice, and soon communicates with a
small round laminated pouch, through which the biliary secretion
passes to the intestine. This tube forms two abrupt inflections, and
terminates in the branchial cavity near the base of the funnel close to
the proboscidian end of the oviduct.

The epithelium of the oesophagus and ingluvies is developed into a
thick cuticular membrane, with minute ridges in the gizzard. In the
specimen dissected by me the crop and gizzard were laden with the frag-
ments of a small crab, the pieces being more comminuted in the gizzard.

The liver is a bulky gland, extending on each side of the crop as
low down as the gizzard ; it is divided into four lobes, connected
posteriorly by a fifth transverse portion : the lobes are subdivided into
numerous lobules of an angular form. The secretion of the bile is
derived, as in other mollusks, from arterial blood ; it is conveyed
from the liver by two main trunks, which unite into one duct, about
two lines from the laminated sac. The bile, having entered the
sac, is diverted by a peculiar development and disposition of one
of the laminae from flowing towards the gizzard. The follicular
structure of this and the other folds of membrane indicate their
glandular character; and the entire laminated pouch may be con-
sidered as a more developed form of pancreas than the simple
caecum which represents that gland in some of the Gasteropods.
No other foreign secretion enters the alimentary canal, as there is
not any ink-gland in the Pearly Nautilus.

The heart and large vessels, with their follicular appendages, are
contained in a large cavity, subdivided into several compartments,

Y 2

324

LECTLKE XXIII.

which I have termed pericardium ; it is separated from the branchial
cavity by a strong membranous partition, in which the following ori-
fices are observable. In the middle the termination of the rectum,
to the right of this the orifice of the oviduct, and on each side at the
roots of the anterior branchiae there is a small mamillary eminence
with a transverse slit, which conducts from the branchial cavity to
one of the compartments of the pericardium containing two clusters
of venous glands. There are also two similar, but smaller, slits con-
tiguous to one another, near the root of the posterior branchia on
each side. These, which seem to have been overlooked in my first dis-
section, were detected by M. Valenciennes in the specimen of the
Nautilus Pompilius which he has recently described* ; and I have ob-
served them in that subsequently presented to the College by Capt.
Sir E. Belcher. They lead to the compartments which I formerly
described and figured f, containing the posterior clusters of the
venous follicles. These compartments M.Valenciennes regards as
shut sacs, communicating only by the above-mentioned apertures
with the branchial cavity.

The venous branches, from the labial and digital tentacles, and
adjacent parts of the head and mouth, terminate with those from the
funnel in the sinus, partly excavated in the body of the cartilaginous
skeleton, and in part continued round the oesophagus. From this
sinus, the great vena cava(^^. 132. a) is continued, running in the in-
terspace of the shell-
^•^^ F=t^3z^gj muscles on the ven-

tral aspect of the ab-
dominal cavity, and
terminating within
the pericardium by a
slight dilatation (c),
which receives by
two veins (d) the
blood from the difFer-
ent viscera. The vena
cava is separated by
a layer of decussat-
ing muscular fibres
from the abdominal
cavity, which closely
adheres to the pa-
rietes of the vein.

S'aurilus Pompilius

♦ Archives du Museum, p. 257. 4to. 1839.

t Memoir on the Nautilus, p. 32. 1832. Plate 5. u, u.

CEPHALOPODA. 325

There are several small intervals left between the muscular fibres and
corresponding round apertures (b) in the membrane of the vein and
peritoneum. This communication, with the general abdominal cavity,
is similar to that already noticed in the Aplysia*: M.Valenciennes
detected the same structure in the specimen of the Nautilus dissected
by him.-|-

The branchial circulation may be considered to commence, when
the blood again begins to move from trunk to branches, four of
which are continued from the terminal venous sinus to convey the
carbonized blood to the four gills, of which there is a larger (and a
smaller one) on each side. Each pair of gills is connected by a
common peduncle to the inner surface of the mantle ; the larger
branchia consists of a central stem supporting forty-eight vascular
plicated lamellae on each side : the smaller branchia has thirty-six
similar lamellae on each side.

The four yesseh(f,f) continued from the venous sinus have attached
to them, in their course to the gills, clusters of glandular follicles
(ff, ff) of a simple pyriform figure : each vessel has three clusters of
such glands contained in the membranous receptacles above men-
tioned. The walls of these receptacles exhibit in some parts a fibrous
texture, apparently for the purpose of compressing the follicles, and
discharging the contents of the membranous receptacles into the
branchial cavity, by the apertures above mentioned at the base of the
gills. Doubtless, therefore, the glands are eraunctories, and eliminate
from the venous blood an excretion, most probably analogous to
urine. Their analogues exist in the higher Cephalopoda, in which
they are considered to act as kidneys by Mayer ; and it is more
philosophical to conclude that the organs of so important an excretion
should be present in all the class, than that they should be represented
by the ink-gland and bag, which are peculiar to one order.

The veins (/, /) extend beyond the follicles each to the root of its re-
spective gill, where it receives a small vein. At this part there is a valve
(A) which opposes the retrogression of the blood ; the vessel, which may
now be termed branchial artery, penetrates the root of the gill (2), and
dilates into a wider canal, which is continued through the soft white
substance forming the branchial stem. A double series of branches
are sent off from the lateral lamellae, which ramify and subdivide to
form the capillary plexus, from which the returning vessels terminate
in the branchial vein. These veins (/, /) quit the roots of the gills,
and return to terminate at the four corners of a subquadrate trans-
versely elongated ventricle (m). From this ventricle two arteries

* P. 301. t Loc. cit. p. 287.

Y 3

326 LECTURE XXIII.

arise, one superior and small (w), the other inferior (r), and strength-
ened by a muscular bulb (§') to the extent of nearly half an inch.
An elongated pyriform sac (o) is attached by a contracted origin
near the root of a large aorta, and dilates to a width of two lines ;
then, again contracting, becomes connected by its other extremity
to the venous sinus : it contained a firm coagulated substance.
M. Valenciennes does not appear to have noticed this peculiar
organ. The anterior aorta supplies the nidamental gland, and ad-
joining part of the mantle, and the rectum ; then bends back to form
the small artery (jl»), continued along the membranous siphon (s).
The large aorta supplies the gizzard and ovary, winds round the
bottom of the abdominal sac, sends off large branches to the liver, and
regains the dorsal aspect of the crop along which it passes to the
oesophagus, distributing branches on either side to the great shell-
muscles. It bifurcates near the beginning of the oesophagus, and
terminates by furnishing branches to the mouth, the surrounding
parts of the head and funnel.

The female organs of the Nautilus consist of an ovary, an
oviduct, and, as in the Pectinibranchiate Gasteropods, of an ac-
cessory glandular nidamental apparatus. The ovary (Jig. 129. u)
is situated at the bottom of the sac on the right side of the
gizzard in a peritoneal cavity peculiar to itself. It is an oblong com-
pressed body, one inch and a half in length, and an inch in breadth ;
convex towards the lateral aspect, and on the opposite side having
two surfaces sloping away from a middle longitudinal elevation. At
the anterior and dorsal angle there is an orifice about three lines in
diameter, with a puckered margin, which conducts into the interior of
the ovary. It is filled with numerous oval ovisacs of different sizes,
which are attached by one extremity to the ovarian capsule^ but are
free and perforated at the opposite end ; are smooth exteriorly, but
rugose and apparently granular on the inner surface, owing to nu-
merous minute wavy plicae adhering thereto. The largest of the
ovisacs were four or five lines in length ; they were principally at-
tached along the line of the exterior ridge, at which part the nutrient
vessels penetrated the ovary.

The oviduct (Jig- 129. ^^) is a flattened tube of about an inch in length,
and from four to five lines in breadth ; it extends forward by the side
of the intestine^ and terminates at the base of the funnel close to the
anus. It becomes enlarged towards the extremity, and is deeply
furrowed in the transverse direction both within and without ; the
parietes are also here thick and pulpy, and apparently glandular. It
is probable, however, that the ova derive an additional exterior co-
vering and connecting substance from the secretion of a large glan-
dular apparatus, which is situated immediately below the terminal

CEPHALOPODA. 327

orifice of the oviduct. This apparatus is attached to the mantle, and
gives rise to the two rounded convexities observable on the ventral
aspect of the body behind the funnel. It is a transversely oblong
mass, composed of numerous close-set pectinated membranous la-
minae, which are about a quarter of an inch in depth, and are dis-
posed in three groups ; those of the larger group extend transversely
across the mesial line of the body, and are unprotected by a mem-
brane ; but the two smaller divisions are symmetrically disposed, and
have the unattached edges of the, laminae covered by a thin membrane,
which is reflected over them from the anterior margin of the glandular
body. These divisions form the sides and anterior part of the gland ;
and as the secreted matter must pass backwards to escape from be-
neath the margin of the protecting membrane, this membrane may
serve both to conduct the secretion nearer the orifice of the oviduct,
and also to prevent its being drawn within the respiratory currents of
water, and so washed away as soon as formed.

In contrasting the organisation of the Nautilus with that of the in-
ferior Mollusca treated of in the two preceding lectures, we find the
main advance to have been made in the organs of animal life.

A true internal skeleton is established in the Nautilus, and thus the
lowest Cephalopod offers an approximation to the Vertebrate type,
which not even the highest of the Articulate series had attained.
Perfect symmetry now reigns throughout the animal and vital organs.
The muscular system forms a larger proportion of the body, with various
arrangements and complications unknown in the lower Encephalous
mollusks. The respiratory tube, though still completed by the over-
lapping, not by the coalescence, of its side-walls, has received an
enormous development as contrasted with the siphonated Trachelipods;
and, by its powerful muscles and their firm cartilaginous basis of
attachment, it is evidently endowed with a new function, in relation
to propelling the Cephalopod with its testaceous dwelling through the
sea.

The nervous centres concentrated in the head have received a marked
increase of bulk, which, nevertheless, is still manifested more strongly
in the inferior masses, and especially the anterior subcesophageal ring
than in the superior or cerebral part. Here, however, we find for the
first time in the Molluscous series, especial ganglions subordinated to
the greatly enlarged organs of vision.

The organs of reptation, which had progressively advanced (as La-
marck's denomination of the higher Gasteropods indicates) towards
the head, are exclusively attached to that part in the Nautilus, and
project from before the eyes and mouth. The mouth, besides its jaws
and spiny tongue, is now served by organs of prehension ; and it is

Y 4

328 LECTURE XXIII.

most interesting to observe that these cephalic tentacula, at their first
appearance, manifest the vegetative character in their multiplied re-
petition and comparative simplicity, compared with their analogues
in the superior Cephalopods.

Some of the Gasteropods have a pair of jaws working upon each
other, but in the horizontal plane, as in insects : in the Nautilus they
are opposed to each other vertically, as in the Vertebrate series, and they
present a form which is repeated amongst fishes by the Scari, amongst
reptiles in the Chelonia, and almost universally in the class of Birds.
The close resemblance to the latter class which the Nautilus offers in
the modifications of the alimentary canal is sufficiently striking, but
hardly more so than that the radiated animalcules presented, in which
we discerned the germs, as it were, of the great molluscous branch of
the Animal Kingdom.

In the very few conchiferous Gasteropods that are able to swim, the
shell is of diminutive size, of a simple form and structure, and of an
extremely light and delicate texture. The strong and muscular oc-
cupant of the Pearly Nautilus-shell would not have been able, not-
withstanding its higher organization, to have risen and swam on the
surface of the ocean unless it had been relieved from the impediment of
its large and dense abode by the introduction of some special mo-
dification in the testaceous structure.

This is effected by the adoption, in the Nautilus, on a more definite
plan and larger scale, of the second mode of dealing with the part of
the shell successively vacated during the rapid growth of the animal,
which has been defined in the general account of the structure and
formation of univalve shells given in the foregoing lecture.* The
abdominal part of the mantle of the Nautilus is attached to the
inner surface of the shell by the intervention of a horny or epithelial
cincture, the expanded lateral portions of which serve as the medium
of insertion of the adherent muscles of the shell : the cavity of the
shell posterior to this attachment is thus hermetically closed. A
third point of attachment is to the bottom of the shell by the pos-
terior extremity of the mantle, which probably presents a conical
form in the embryo Nautilus. The line of attachment of both the
muscles and the cincture progressively advances with the growth of
the animal. A certain portion of the fundus of the shell thus becomes
vacated, and the Nautilus commences the formation of a new plate
for the support of the part of the body which has been withdrawn
from the vacated shell. The formation of the plate proceeds from
the circumference to the centre, and there meeting the conical pro-
cess of the mantle, which retains its primitive attachment, the calcifi-
cation is continued backwards for a short distance around that pro-

* P. 297.

CEPHALOPODA. 329

cess, which now forms the commencement of the membranous siphon,
and acquires the partial protection of the calcareous tube. An air-
tight chamber is thus formed, traversed by the siphon, which per-
forates its anterior wall or septum; by a repetition of the same
processes, a second chamber is formed, included within two perforated
septa; and similar, but wider partitions continue to be added, con-
currently with the formation of the new layers which extend and
expand the mouth of the shell, until the animal acquires its full growth,
which is indicated by the body having receded for a less distance
from the penultimate septum before the formation of the last septum
is begun.

The periodical formation of these septa in the progress of growth
is analogous to that of the projecting external plates in the Wen-
dletrap, and of the rows of spines in the Murex ; but these ex-
ternal processes consist of the opake calcareous layer of the shell,
whilst the internal processes in the Nautilus consist of the nacreous
layer like the septa in the Turritella. Thus the embryo Nautilus
at first inhabits a simple shell like that of most univalve MoUusca,
and manifests, according to the usual law, the most general type at
the early stage of its existence ; although it soon begins, and ap-
parently before having quitted the ovum, to take on the special form.

In acquiring the camerated structure of the shell, the Nautilus
gains the power of rising from the bottom and the requisite condition
for swimming ; by the exhalation of some light gas into the deserted
chambers, it attaches to its otherwise too heavy body a contrivance
for ascending in its atmosphere, as we ascend in ours by the aid of
a balloon. But the Nautilus, superior to the human aeronaut,
combines with the power of elevating and suspending itself in the
aqueous medium, that of opposing its currents and propelling
itself at will in any direction. It possesses the latter essential adjunct
to the utility of the balloon as a locomotive organ, by virtue of the
muscular funnel, through which it ejects into the surrounding water,
doubtless with considerable force, the respiratory currents.

It appears that the proportion of the air chambers to the dwelling
chamber of the Nautilus and its contents, is such, as to render
it of nearly the same specific gravity as the surrounding water.
The siphon, which traverses the air chambers, communicates with
the pericardium, and is most probably filled with fluid from that
cavity.

Dr. Buckland conjectures that the Nautilus may possess the power
of ejecting such fluid into the siphon, and thereby of compressing the
gas of the chambers and increasing the specific gravity of the shell.
Such, indeed, were the siphon dilatable, would be the natural effect

330 LECTURE XXIII.

of the contraction of the animal within its shell. The consequent
pressure of the dense anterior muscular segment upon the soft
and yielding visceral cavity, resisted at the same time by the
unyielding posterior plate at every point, save that from which the
siphon was continued, would propel into that tube as much fluid as it
might be capable of receiving. These consequences would follow
the instinctive retraction of the animal when alarmed ; and if they
should take place while it was floating on the surface, it would im-
mediately begin to descend. If, desiring to rise again from the
bottom, the Nautilus should protrude its body from the mouth of the
shell, extend the folds of its mantle, and spread abroad its tentacula^
it would withdraw the pressure from the abdomen, and, by the act of
advancing, create a tendency to a vacuum in the posterior part of
the shell. The fluid in the siphon would then, if that tube were con-
tractile, return into the pericardial cavity, the gas in the chambers
would expand, and the specific gravity of the animal be sufliciently
diminished to cause the commencement of its ascent, which would
doubtless be accelerated by the reaction of the respiratory currents
upon the water below.

Neither the contents, nor the vital properties of the siphon
are however yet known : an artery and vein are assigned for
its life and nutrition : but the structure of the membranous
siphon, in the specimens from which I have had the opportunity of
examining it in a recent state, presents, beyond the first chamber, an
inextensible and almost friable texture, apparently unsusceptible of
dilatation and contraction : it is also coated beyond the extremity of
the short testaceous siphon with a thin calcareous deposit. A graver
objection to the hydrostatic action of the siphon is founded upon its
structure in certain extinct species of Nautilus, as the iV. Sipho, in
which it is provided through its whole extent with an inflexible outer
calcareous tube, rendering it physically impossible that the gas of the
chambers could be affected by any difference in the quantity of fluid
contained in the siphon. In the Nautilus striatus, also, the calcareous
siphon is a continuous tube, slightly dilated in each chamber.

From these facts I incline rather to the conclusion, that the sole
function of the air-chambers is that of the balloon, and that the
power which the animal enjoys of altering at will its specific gravity,
must be analogous to that possessed by the fresh-water testaceous
Gasteropods, and that it depends chiefly upon changes in the extent
of the surface which the soft parts expose to the water, according as
they may be expanded to the utmost, and spread abroad beyond the
aperture of the shell, or be contracted into a dense mass within its
cavity. The Nautilus would likewise possess the additional advantage
of producing a slight vacuum in the posterior parts of the chamber of

CEPHALOPODA. 331

occupation which is shut out by the horny cincture, and muscles of
adhesion from the rest of tliat cavity.

Whatever additional advantage the existing Nautilus might derive,
by the continuation of a vascular organised membranous siphon
through the air-chambers, in relation to the maintenance of vital
harmony between the soft and testaceous parts, such likewise must
have been enjoyed by the numerous extinct species of the tetra-
branchiate Cephalopods, which, like the Nautilus, were lodged in
chambered and siphoniferous shells.

If the Nautilus extended itself in a straight line during its growth,
instead of revolving round an imaginary axis, a straight conical shell
would be produced, with the chambered part divided by simple septa
concave next the outlet. Such are, in fact, the characters of the
fossil shells called Orthoceratites. The siphon is usually central, but
sometimes marginal ; it is testaceous throughout, and generally moni-
liform or dilated at each chamber ; this structure Dr. Buckland re-
marks, would admit of the distension of a membranous siphon. Mr.
Stokes has discovered in a species of Orthoceratite from Lake Huron,
a second calcareous siphon included within the moniliform siphon,
which shows no corresponding partial dilatations, but is connected
to the external siphon by successive series of radiating tubuli ; the
inner siphon was probably produced by a calcification of the mem-
branous siphon, and of processes continued from it at regular intervals.
The complex siphons of these Orthocerce are of great relative capacity,
and the species so characterised have been separated from the simple
Orthoceratites under the subgeneric name Actinoceras.

I have already alluded to the slightly undulating contour of the
margins of the septa in the Nautilus, which makes the surface next
the aperture of the shell convex at one part and concave at another.
In an extensive genus of extinct chambered shells called ' Am-
monites,' the sinuosity of the margins of the septa is much greater,
and most of the surface next the outlet is convex : the siphon per-
forates the septa at their centre in extremely few species, and in the
rest is situated at that margin which is next the outer curve or cir-
cumference of the shell. Certain chambered shells thus character-
ised are straight, like the Orthoceratites, but generally compressed,
with their numerous septa joining the outer shell by foliated denta-
tions : they are termed Baculites. In the true Ammonites the shell
is discoid and coiled upon itself as in the Nautilus ; but it is strength-
ened by arched ribs and dome-shaped elevations on the convex sur-
face, and by the tortuous windings of the foliated margin of the
transverse partitions. Separate casts of the interior of the chambers
are not unfrequently obtained, which have become detached by the
solution of the calcareous walls and septa of the shell, or are held to-

332 LECTURE XXIII.

gether by the dove- tailed lobes of the margins of the chambers. The last
chamber of the Ammonite was of large size, as in the Nautilus, and
doubtless contained all the soft parts of the animal save the small pro-
portion which was prolonged into the siphon. Certain species, re-
cently described by Mr. Pratt from the Oxford clay, were characterised
by the production of a long and narrow process from each side of the
mouth of the shell, indicating a corresponding modification in the
lobes of the mantle, analogous to that which produces the auricular
appendages of the mouth of the shell in certain Argonautae. The
same gentleman has likewise recently shown me a small Ammonite in
which the mouth of the shell is arched over transversely by a convex
plate of calcareous matter continued from the lateral margins of the
outlet, and dividing this into two apertures, one corresponding with
that above the hood of the Nautilus, which gives passage to the
dorsal fold of the mantle ; the other with that below the hood, whence
issue the tentacles, mouth, and funnel : such a modification, we may
presume, could not take place before the termination of the growth of
the individual.

The Turrilite is essentially an Ammonite disposed in spiral coils.
The Hamites and Scaphites are other modifications of the outward
form of similarly-constructed chambered shells : in the former the
small extremity of the shell is curved, the rest being straight ; in the
latter both ends are curved towards each other like those of a canoe.
With none of these species has there ever been found a trace
of the ink-bag ; a part, indeed, of so delicate a texture that some
surprise may be excited in such of my hearers as are not conversant
with the wonders of geology, that any evidence of its existence could
be expected to be met with in a fossil state.

I shall, however, conclude this Lecture by bringing before you ex-
amples in which not only the ink-bag but the muscular mantle, the fins,
the eyes, and the tentacles and their horny hooks, of extinct Cephalopods
have been preserved from the remote periods of the oolitic deposits
to the present time. Independently of these and many other ex-
amples of the durability of the inky secretion of the gland which is
peculiar to the naked Cephalopods, the absence of the organ in the
shell-clad Nautilus, too well protected to need such means of temporary
concealment, would lead to the inference that the ink-bag must have
been absent in the other low-organised Cephalopods covered by
chambered siphoniferous shells.

A more complicated fossil shell than any of the preceding, but
allied to them by the camerated and siphoniferous structure of one
of its constituent parts, has occasioned much perplexity amongst
Palaeontologists ; the evidence of its nature has however for some

CEPHALOPODA.

333

years been in the main sufficient, in my opinion, to determine its affi-
nities: but as the value of this evidence could only be appreciated by
those who had studied the laws of correlation of the cephalopodic
structures, it failed to produce general conviction ; and the additional
facts which I am able to-day to bring before you will not, therefore, be
unacceptable. The shell to which I allude is that called the '.Be-
lemnite,' which is associated with the more obvious congeners of the
Nautilus through a considerable range of the secondary rocks.

The chambered part of the shell of this extinct Cephalopod has the
form of a straight rone {fig. 133. &), the septa being numerous, with a
slight and equable concavity directed towards
the outlet or base of the cone. The inter-
vening chambers are so shallow that the septa
have been compared to a pile of watch-glasses.
The septa are chiefly composed of nacreous
substance, with a thin layer of opake and
friable calcareous matter on both surfaces,
and the entire cone is enveloped in a sheath
of opake calcareous matter lined with na-
creous substance, and having on the outer
surface, or there degenerating into, a pellicle
or thin layer of a horny substance. This latter
horny or albuminous tissue is continued
forwards beyond the base of the chambered
cone*, and forms the parietes of a cavity (a)
containing some of the viscera of the animal.
The chambered cone itself, with its
sheath, is lodged in a conical cavity or
alveolus f excavated in the base of a long
conical or fusiform, sometimes compressed,
spathose body (c), resembling the head of a
dart or javelin, whence the name ' Belem-
nite,' applied to this genus of extinct
Cephalopods. This spathose sheath or
guard of the chambered cone is most com-
monly found detached from the rest of the
shell, with its thin aveolar portion fractured, especially when fu-
siform and in the younger Belemnites, when it is pointed at both
ends. In this state it has been mistaken for the spine of an Echino-
derm. This opinion of Klein has been reproduced in later times by

* ' Phragmocone.'

t The term alveolus has been given improperly to the contents of the socket,
▼iz to the ' phragmocone.'

Belemnite restored.

334 LECTURE XXIII.

M. Raspail ; but the instances of discovery of the guard associated with
the chambered cone left no room for doubting its relationship with the
Orthoceratites, although the precise degree of that relationship re-
quired much additional evidence for its determination.

The spathose guard consists of successive layers, of which the exterior
ones run parallel with the outer surface, and progressively increase in
length as they approach it, thus forming the conical cavity for the lodge-
men of the chambered shell. The innermost or first-formed layers of
the guard are not parallel with the outer ones, but recede from them
at their upper extremity, where they form a point, and sometimes a
dilated nucleus, in contact with the apex of the chambered cone.
The interspace thus left between the early and the later strata of the
guard is occupied by the coarse calcareous matter continued from
the sheath of the chambered cone, and a filamentary process of
apparently the same matter is continued down the centre of the
guard to its apex.

The structure of the spathose layers of the guard is fibrous ; the
fibres being directed at right angles to the plane of the strata : viewed
in thin sections by transmitted light it bears a close resemblance
to that of the teeth of Pycnodont fishes, but certain proportions
of the transverse fibres are apt so to intercept the light as to cause
the appearance of elongated triangular dark specks, with their apices
directed sometimes to the periphery, and sometimes to the centre of
the guard. The microscopic structure proves this heavy spathose
aggregation of subtransparent calcareous matter to be the effect of
original formation, and not, as Walsh, Parkinson, and Lamarck
supposed, of infiltration of mineral substance into an originally
light and porous texture. Here is a section of a Belemnite*, in
which the chambers of the cone have been filled with crystalline
matter infiltrated from the water of the stratum in which the dead
shell was imbedded ; and you have a favourable opportunity of con-
trasting the crystalline condition of this infiltrated matter with the
organised texture of the solid guard.

The exterior surface of this guard always exhibits, when perfect or
entire, traces of vascular impressions : it is sometimes granular, and
presents other modifications, which prove that it was covered by an or-
ganised membrane in the living Cephalopod. I have occasionally seen
the remains of a more immediate investment by a thin friable layer of
calcareous matter analogous to that of the outer layer of the sheath of
the chambered cone, with which layer it becomes continuous. The
exterior of the spathose guard is generally impressed with a longi-
tudinal groove extending from the apex upwards.

* No. 1056. A.

Cephalopoda. 335

The septa of the chambered cone are perforated by a marginal
siphon, situated in most Belemnites on the side which is nearest the
before-mentioned line or groove ; but in certain species of Belem-
nites, characterised by the flattened form of the spathose guard, the
siphon is on the opposite side. These Belemnites, which at first sight
look like distorted or accidentally compressed specimens, are peculiar
to certain members of the green sand formation, called the ' older
Neocomian.' In some species the exterior of the guard is impressed
with two opposite longitudinal channels in addition to the primitive
and constant one.

Specimens of Belemnites have been discovered in which the spathose
guard has been fractured during the lifetime of the animal ; but the
broken portions have been held together by the investing organised
integuments, and have been reunited by the disposition of new layers
of the fibrous structure peculiar to the guard. *

The existence of a camerated and siphoniferous structure on this
complex and remarkable shell, induced most Zoologists to class it with
the Ammonites and other more simple chambered shells. Mr. Miller
having detected evidence of the internal position of the Belemnite in
the exterior characters of the guard, first ventured upon a conjectural
restoration of the entire animal f ; and as only the dibranchiate type
of Cephalopods was then known, he placed it in the body of a
Calamary (^Loligo), assigning to the terminal fins the office of clasping
the guard and retaining it in its proper position.

The first evidence that bore directly upon the position of the Be-
lemnite in the Cephalopodic class was detected by Drs. Buckland and
Agassiz in specimens of Belemnite from Lyme Regis, in which the
fossil ink-bag and duct was preserved in the basal chamber of the
phragmocone. We must connect with this fortunate discovery the im-
portant fact, that remains of an ink-bag have never been" met with in
connection with any of the more simple or typical forms of chambered
shells: we know that the ink-bag does not exist in the recent Nautilus ;
and it will be shown in the following Lecture that it is present in all
the existing Cephalopods which possess more or less rudimental in-
ternal shells. I ought here, perhaps, to anticipate, or recapitulate the
relations of co-existence of the ink-bag with the organization of the
naked Cephalopods, which I pointed out, in 1832, in my description
of the Nautilus Pompilius. The highly organized naked Cephalopods
enjoy active powers of locomotion, which would be incompatible
with the incumbrance of a large external protecting shell ; but, to
compensate for the want of this defence, nature has provided them
with the power of secreting an inky fluid, which, when alarmed, they

* Duval- Jouve, Memoire sur les Belemnites. 4to. 1841. pi. x.
f Geological Transactions, N. S. vol. ii. p. 45. pi. ix. 1823.

33G LECTURE XXI J I.

eject into the surrounding water, and are concealed by the obscurity
which they thus occasion. The branchial character of the naked
Order of Cephalopods is an essential condition of their muscular
powers. The presence of an ink-bladder, therefore, in the extinct
BelemniteSj would have implied the internal position of the shell,
even if other proof had been wanting ; and, by the laws of correla-
tion, it implies likewise the presence of the muscular forces for rapid
swimming, and the concomitant conditions of the respiratory, the
vascular, and the nervous systems. Connecting, therefore, all these
considerations with the detection of the ink-bag in the shell of the Be-
lemnite, I could not hesitate in refering the Belemnites, and likewise
the Spirula, on account of the ascertained internal position of its shell,
to the Dibranchiate order, and I, therefore, separated these cham-
bered and siphoniferous shells from the Nautilus and the Ammonites
in the Classification of the Cephalopoda submitted to the Zoological
Society in February 1836.

But the true grounds of this separation seem not to have been
understood by some Palaeontologists. Professor Phillips, for example,
in his excellent Article on Turrilites in the part of the Penny Cyclo-
paedia, published in January of the present year, has observed, " The
relations of Turrilites, Scaphites, Baculites, and Hamites to Ammo-
nites is very obvious ; and, as through Goniatites, this great extinct
group is certainly connected to the living and extinct Nautili,
Mr. Owen has ventured to include them all in the Tetrabranchiate
Cephalopoda (^Cephalopoda), leaving Spirula and the Belemnites
with Sepia and the Dibranchiate types. However this may be, the
determination of the relative affinities among the numerous fossil
Cephalopods, a point of great importance, must be worked out with
the help of other considerations than the respiratory system." I have
said enough to show that many other considerations than those of the
respiratory system, and of equal importance with them, influenced
me in the determination of the natural affinities of the Belemnites.
Leopold Von Buch, who believed that he could trace in certain slabs
containing Belemnites the impressions of the Cephalopods to which
they belonged, concluded " that the body of the animal enveloped
the greater part of the shell, and exceeded its length by eight or ten
times." * Other considerations, taken from the shell itself, prove,
as has already been shown, that it was wholly internal.

M. Duval, the latest and most accurate author on fossil Belemnites,
reproduces the figure which M. D'Orbigny has published, and which
is essentially the same as that given by Dr. Buckland in his Bridge-

* Oken's Isis, Bd. xxi. p. 438.

CEPHALOPODA. 337

water Treatise ; and, like it, differs from Mr. Miller's restoration,
only in the position of the ink-bag and in the extended state of the ter-
minal fins. With respect to these parts, ]M. Duval, from his dis-
covery of the united fractures of the spathose guard, objects, with
much acumen, that, if the fins of the Belemnite had been placed at
the side of the guard, they must have been rendered useless by its
fracture, and the creature, thus deprived of its power of swimming,
would soon have fallen a prey to its numerous enemies, and would
not have survived to exemplify the reparative powers of those ancient
Cephalopods. M.Duval, however, modestly concludes by confessing
that he should not have dared himself to figure from the known anal-
ogies, the animal to which the Belemnite ought to have belonged ;
for " I have not," he says, " a sufficiently exact knowledge of the
organic laws of the Cephalopoda." * It seemed vain to hope that
the soundness of the principles on which the classification of the
Belemnites with the dibranchiate Cephalopods had been definitely
proposed, should ever be vindicated by an example of parts appa-
rently so perishable as the mantle, the fleshy arms and fins of these
Mollusca. I have however the gratification to be enabled, by the
kind permission of the Marquis of Northampton, to place before
you a specimen of a Belemnite, in which not only the ink-bag
but the muscular mantle, the head, and its crown of arms, are
all preserved in connection with the Belemnitic shell. It appears
to have been the peculiar property of the matrix, in which this and
many similar valuable and instructive specimens were entombed, to
favour the conversion of the muscular tissue into adipocire, and its
subsequent preservation to the present time. Yet this matrix is a
member of the Oxford-clay-formation, belonging to the middle oolite
system ; older, therefore, than the Portland stone, the Wealden and
the Cretaceous group. The Cephalopod, in which we may now study
the microscopic character of the muscular fibre, must therefore have
existed at a period antecedent to the gradual deposition of these
enormous masses of the secondary strata, which themselves preceded
the formation of the entire tertiary series, and the overspreading
unstratified masses called diluvial. The attempt to conceive or cal-
culate the period of time which must have elapsed since the Belem-
nites were thus embalmed, baffles and awes the imagination.

A second, less complete, but highly instructive, specimen of the
Belemnite, from the collection of Mr. Pratt, to whom I am indebted
for the first knowledge and inspection of the soft parts of these extinct
Cephalopods, exhibits the contour of the large sessile eyes, the funnel,

* Loc. cit. p. 20.

z

338 LECTURE XXIII.

a great proportion of the muscular parts of the mantle, and the
remains of two lateral fins, the ink-bladder and duct, and a con-
siderable portion of the chambered cone. The two fins (Jig. iS3.
/, /) present the form of flattened transversely striated fibrous
masses with their free border entire and rounded. They are situ-
ated on each side of the visceral cavity, and demonstrate the ac-
curacy of M. Duval's objection to their position in the previous con-
jectural restorations. A large tract of the grey fibrous substance,
running parallel with and to one side of the remains of the head,
indicates the position of the infundibulum, and is terminated by a
concave truncation. At the middle of the visceral mass at the
interval of the two lateral fins, there lies a compressed body of a
horny texture and somewhat bilobed form, on which may be clearly
distinguished striae passing outwards in opposite directions from a
middle line, and diverging from each other in their course, which
resembles that of the fibres of the digastric muscle in the gizzards of
the Cephalopods : this apparent remnant of the stomach lies anterior
to the ink -bladder. There is a strong negative evidence that the
Belemnite possessed horny mandibles like the other naked Cepha-
lopods, since no calcareous ones or Rhyncholites have been dis-
covered associated with these remains. The cephalic arms, which
are preserved, belong to the normal series, and were eight in number :
they were provided, not with simple acetabula, but with a double
alternate series of slender elongated horny hooks, as in the genus of
existing Calamaries, called Onyclioteuthis* Each arm seems to have
been provided with from twelve to twenty pairs of these hooks. They
were doubtless developments of the horny hoop which encircles the
central process of the acetabulum, as in the modern Onychoteuthides ;
but in the position of the pallial fins, the Belemnite resembled the
Sepiola. The traces of the superadded pair of tentacula are some-
what doubtful.

The modern decapodous Cephalopod, which most nearly resem-
bles the Belemnite in the structure of its internal shell, is the Sepia,
or common cuttle-fish ; the lateral fins of this species extend from
the apex to near the base of the mantle. The nucleus, or terminal
spine of the cuttlebone corresponds with the spathose guard of the
Belemnite : the convex posterior broad layer of friable calcareous and
horny matter is analogous to the enveloping cone ; but its margins,
instead of being approximated and soldered together, are free and
lateral in position : the successive plates, embedded in its concavity,
answer to the camerated cone of the Belemnite ; but, instead of
being perforated by one or many siphons, they are connected with
each other by a series of minute undulating lamellae.

CEPHALOPODA. 339

Thus we have at length been furnished with the proof of the di-
branchiate nature of the Belemnite, and we learn from the sau^e
ocular evidence that it combined characters at present divided be-
tween three distinct genera of the order ; namely, first the calcareous
internal chambered shell, to which the Sepia offers the nearest ap-
proach ; secondly, the formidable hooks of the arms, which charac-
terise the modern genus Onychoteuthis ; and, thirdly, the limited
attachment of the lateral fins to a position a little in advance of the
middle of the body, as in the Sepiola.

The Belemnite, having the advantage of its dense but well-balanced
internal shell, must have exercised its power of swimming backwards
and forwards, which it possessed in common with the modern Decapod
Dibranchiata, with greater vigour and precision. Its position was
probably more commonly vertical than in its recent congeners. It
would rise swiftly and stealthily to infix its claws in the belly of a
supernatant fish, and then, perhaps, as swiftly dart down and drag
its prey to the bottom and devour it. We cannot doubt at least but
that, like the hooked Calamaries of the present seas, the ancient
Belemnites were the most formidable and predacious of their class.

LECTURE XXIV,

CEPPIALOPODA.

The deductions which were founded on the modifications of the
chambered siphoniferous shell and other enduring remains of the
very remarkable extinct genus which occupied our attention at the
close of the last lecture, obliged me frequently to refer to the type of
structure which characterises the DibrancJiiate order of Cephalopods,
and which places these Mollusca not only at the head of that
division of the Animal Kingdom, but, in respect of its closer
proximity to the Vertebrate type, unquestionably at the head of the
whole Invertebrate series.

The body of the Dibranchiate Cephalopod is divided, as in the
Nautilus, into two parts ; a head, containing the organs of sense,
mastication, and deglutition, and supporting the prehensile and prin-
cipal organs of locomotion, and a trunk or abdomen, consisting of a
muscular sac or mantle, with a transverse anterior aperture, and con-
taining the respiratory, generative, and digestive viscera. With one

z 2

340 LECTURE xxir.

exception the mantle is naked, and includes a more or less rudimental
shell ; and it supports, in most of the species, a pair of fins. In a
single genus it is contained in a light and symmetrical monothalamous
shell. Compared with the Nautilus, the cephalic tentacula are much
reduced in number, the external ones, continued from the oral sheath,
not exceeding eight, to which, in most of the genera, is added a pair
of internal and much longer tentacula. The arms are much increased
in size and of a more complicated structure, supporting on their in-
ternal surface numerous suckers, and sometimes connected together
by powerful muscular web. The eyes are much larger and more
complex, are no longer pedunculated, but lodged in orbits. The
mouth is armed with two piercing and trenchant horny jaws, resem-
bling in shape and in their vertical movements those of the Nautilus.
The gills are two in number, each with a ventricle expressly appro-
priated to the branchial circulation ; the systemic circulation having
a single muscular ventricle, as in the Nautilus. The infundibulura is
a complete muscular tube, shaped like an inverted funnel. They possess
a gland and membranous receptacle for secreting and expelling
an inky fluid. The sexual organs are in distinct individuals, as
in the Tetrabranchiate order. All the species of both orders of
Cephalopods are aquatic and marine.

The Dibranchiate order may be subdivided into two tribes ; the
one provided with the eight ordinary arms and the two longer ten-
tacles, hence called Decapoda ; the other tribe without the tentacles,
and called Octopoda.

The various forms of the extinct Belemnitidce constituted one
family in the Decapod tribe. The little Sjnrula, characterised by a
less complex, but internal chambered shell, is the type of a second
family. The cuttle-fish, characterised by its internal calcareous shell,
which feebly represents that of the Belemnite, exemplifies a third
family of Decapods called Sepiadce. The common calamary (^Loligo),
in which the internal shell is reduced to a horny quill-shaped plate,
represents the fourth and most extensive family of the present tribe,
which I have called Teuthidce ; and in which one genus (^Onycho-
teuthis) had the caruncle of more or fewer of its acetabula produced
into horny claws. In all the Decapods the mantle supports a pair
of fins, and the siphon is generally provided with a valve.

In the \x\\iQ, Octopoda, fins are rarely developed from the mantle ; but
the eight ordinary arms are longer, thicker, and are united together
by a broader web, which forms a powerful organ for swimming in a re-
trograde direction. One family in this tribe ( Testaced) is represented by
the genus Argonauta, in which, at least in the female sex, the first or
dorsal pair of arms is dilated at its extremity into a broad thin mem-

CEPHALOPODA. 341

brane^ like the mantle in the testaceous mollusks ; by means of these
membranes the animal, in fact, forms for itself an extremely light,
slightly flexible, and elastic, but calcareous, symmetrical shell, which
is simple, and not divided into chambers ; the vacated portion commu-
nicating with the rest, and being used by the inhabitant as the recep-
tacle for the eggs. The siphon is without a valve, but is articulated
at its base on each side to the inner surface of the mantle. The second
family of the Octopods I have termed Nuda, the species not being
provided with an external shell. The first pair of arms is elongated,
and contracts to a point : the funnel or siphon is without an internal
valve or external joints. The rudimental shell is represented by two
short styles, encysted in the substance of the mantle. The typical
genus of this family is termed Octopus, in which the arms are pro-
vided with a double alternate series of sessile acetabula. In a second
genus Eledone, the arms are provided with a single series of a(;etabula.
In the Cirroteuthis a pair of filaments project between each of the
suckers.

The shell or dermal skeleton, which has been progressively reduced
in the present highly organised class, attains its lowest or most rudi-
mental condition in the Octopus and Eledone. The genus in which
the shell most nearly resembles that of the tetrabranchiate Cephalopods,
belongs to the Spirula. A few mutilated specimens which had
reached this country during this present century, had demonstrated it
to be an internal shell, and the more perfect specimen dissected by
M. de Blainville in 1839, proved it to have the characteristic organi-
sation of theDibranchiate order, and to possess, as Peron had indicated,
the eight short arms and the two long tentacula of the Decapodous
tribe. The shell of the Spirula {Jig. 134.) is perfectly symmetrical,
convoluted in a vertical plane with the whorls con-
tiguous, but not touching. The shell commences
by a small oval cell, followed by a series of cham-
bers (6), which rapidly increase in size. The septa
(«) are concave towards the outlet, and are per-
spiruiaaustiaiis. foratcd by a siphon at the internal or concave
margin of the shell. A small funnel-shaped tube (c) is continued
backwards from each perforation ; and its apex penetrates the mouth of
the succeeding tube. The circumference of the siphonic aperture is
impressed, as Mr. Stokes first observed, by a circle of minute pits.
The shell seems to be exclusively composed of a fine white nacreous
substance ; it is imbedded in the posterior part of the mantle, with a
small part of its surface exposed on both the upper and lower sides of
the animal's body : the exposed parts of the shell are invested by a
granular straw-coloured epidermis.

z 3

342 LECTURE XXIV.

The principal characters of the internal shell of the cuttle-fish have
already been pointed out in the illustration of its analogies with that of
the Belemnite. The preparations, Nos. 106, 107, 108, demonstrate the
great proportion of animal membrane which enters into the compo-
sition of this light friable laminated shell.

In the rest of the Decapoda, the rudimental shell consists exclusively
of animal matter, of the consistency of horn, and presents either the
form of a pen, as in the Calamary, or that of a straight three-edged
sword, as in the Onychoteuthis. This body was called ' xiphos' by
Aristotle, and * gladius ' by Pliny. In the Sepioteuthis it is as broad
in proportion to its length as the cuttle bone. In the Onychoteuthis^
LoUgo, and Loligopsis, it is much narrower, but is as long as the mantle.
In Sepiola and Rossia, the gladius, commencing at the anterior
margin of the mantle, ends before it has reached half way down the
back. In the Octopus and Eledone, the last traces of a shell exist in
the form of two small amber- coloured styliform bodies, contained
loosely in capsules in the substance of the mantle.

The skin of the naked Cephalopod is generally thin and lubricous,
and can be more easily detached from the subjacent muscles than
in the inferior Mollusks. In some of the smaller Cephalopods it is
semitransparent ; it is densest in the Calamaries, in which the
epidermal system is most developed, as is exemplified in the horny
rings or hooks upon the acetabula. In the Octopods the epidermis is
reflected over the interior of the acetabula without being condensed
into horn. Upon the body the epiderm may generally be detached in
the form of a thick white elastic semitransparent layer. The second,
or pigmental layer of the skin, analogous to the rete mucosum, con-
sists of numerous cells of a flattened oval or circular form, containing
coloured particles suspended in a fluid. The colour is rarely the
same in all the cells ; the most constant kind generally corresponds
more or less closely with the tint of the inky secretion. In the Sepia
there is a second series of vesicles containing a deep yellow or
brownish pigment : in the Loligo vidgaris there are three kinds of
coloured vesicles, yellow, rose-red, and brown : in the Octopus vid-
garis there are four kinds of vesicles, red, yellow, blue, and black.
In the skin of the Argonauta all the colours which have been ob-
served in other Cephalopods are present, and contained in their ap-
propriate cells. These cells possess the power of rapid alternate
contractions and expansions, by which the pigment can be driven into
the deeper parts of the corium or brought into contact Mith the
semitransparent epiderm. If the skin of an Octopus be slightly
touched, the colour will be accumulated, gradually or rapidly, like a
cloud or a blush upon the irritated surface. If a portion of the skin be

CEPHALOPODA. 343

removed from the body and placed in sea-water under the microscope,
the contractions of the vesicle may be watched for some time : their
margins are well defined, and they pass, during their dilatations or
contractions, over or under one another. The power which the
Cephalopods possess of changing their colour and of harmonizing it
with that of the surface on which they rest, is at least as striking and
extensive as in the Chameleon, in which, it seems, from the latest
observations, to be produced by a similar property and arrangement
of pigmental cells.

The internal organised skeleton of the dibranchiate Cephalopod
is cartilaginous, as in the Nautilus, but consists of a greater number
of pieces, and enters into a larger proportion of the organisation of
the animal. The cranial cartilage is no longer limited in its position
to the under side of the oesophagus, but completely surrounds that
tube, which, together with the inferior salivary ducts and the cephalic
branches of the aorta, traverses a narrow canal in its centre. The
cartilage expands above into the cavity containing the brain, while
below it is excavated to form the organ of hearing, and at the sides
expands into the broad and thick orbital cavities. There is also a
thin and long cartilage which supports the eyeball^ and seems to be
analogous to the ophthalmic peduncle of the Rays and Sharks. A
process continued from the anterior part of the cranial cartilage ex-
pands into a broad transverse plate^ and gives attachment to the
muscles of the arms. The infundibular cartilage, which is a process
of the cranial one in the Nautilus^ is a distinct piece in the Dibran-
chiata. It is of a large size, and of a flattened triangular figure in
the cuttle-fish, in which it is situated above the base of the funnel.
It consists of three distinct portions in the Calamary. On each side
the base of the funnel there is a smooth oblong articular cavity, formed
by a distinct piece of cartilage, which is articulated with a corre-
sponding cartilaginous prominence from the inner surface of the side
of the mantle. These cartilaginous joints of the funnel vary in shape
in the diff'erent genera : they are wanting in the Octopus. The
lateral fins of the Decapoda are each supported by a narrow flattened
elongated cartilaginous plate, which forms the medium of attachment
of the powerful muscles of those fins. These appear to be analogous
to the pectoral fins of fishes ; but as they are not fixed to a vertebral
column, their position is variable ; in the Rossia^ for example, they are
situated near the anterior part of the body ; in the Loligo^ they are
placed at the posterior extremity : in the Sepia they extend, like the
great pectoral fins of the Rays, along the whole side of the body. In
the Octopods the mantle-fins and their cartilages are wanting, except

z 4

344 LECTURE XXIV.

in the anomalous genus Cirroteuthis, in which they are attached io
the anterior part of the sides of the mantle.

The sole locomotive organs in the ordinary Octopods, and the sole
prehensile organs in all the Dibranchiata are the appendages deve-
loped from the head, termed * arms,' ' feet,' ' tentacles,' and ' pro-
boscides.' They have no true homology with the locomotive members
of the Vertebrata, but are analogous to them, inasmuch as they relate
to the locomotive and prehensile faculties of the animal.*

The eight arms of the Octopus commence by a hollow cone of
muscular fibres attached by a truncated apex to the anterior part of
the cephalic cartilage. The fibres are for the most part oblique, and
interlace with one another in a close and compact manner, as the cone
advances and expands to form the cavity containing the mandibulate
mouth, at the anterior extremity of which they are continued forward,
and separate into eight distinct portions which form the arms. The de-
velopment of the eight external arms bears an inverse proportion to that
of the body : they are longest in the short round-bodied Octopi, and
shortest in the lengthened Calamaries and Cuttle-fishes, in which the
two elongated retractile tentacles are superadded by way of compen-
sation. These latter organs are not continued from the muscular
cone, which correspond with the cephalic sheath in the Nautilus, but
arise, like the internal labial processes in that Cephalopod, close to-
gether from the cephalic cartilage, internal to the origins of the
ventral pair of arms. They proceed at first outwards to a large
membranous cavity situated anterior to the eyes, and emerge between
the third and fourth arms on either side.

In most Octopods the two dorsal arms are the longest : they are ten
times the length of the body in Oct. Aranea. But besides their su-
perior length, the dorsal arms present other peculiarities in this
family of Cephalopods : in the genus Argonauta they are provided,
as before stated, with the expanded calcifying membranes, which are
usually spread over the exterior of the delicate shell, meeting and
overlapping each other along its slender keel. The fabled office of
these membranes, as sails to waft the argonaut along the surface of
the ocean, and that of the attenuated arms as oars extending over the
sides of the boat, have afforded a beautiful subject for poetic and
pictorial imagery and philosophic analogy in all ages : and the little
hypothetical navigator of nature's ship has been the subject of the
disquisitions of naturalists from Aristotle to Cuvier, and of the song
of the poet from Callimachus to Byron.

* GeofFroy St. Hilaire regards the cuttle-fish as a vertebrate animal bent double,
with the approximated arms and legs extending forwards : a similar comparison
may be found in Aristotle.

CEPHALOPODA, 345

In the Octopus velifer both the first and second pairs of arms sup-
port broad and thin membranous appendages at their extremities. In
the common Octopus the eight arms are connected together for some
distance beyond the head by membranes and muscles, which form a
circular fin ; this constitutes its sole locomotive organ when swimming,
and, by its powerful contraction, aided, however, by the ejection of the
currents from the funnel, the animal is propelled through the water
by a quick retrograde motion. In the Oct. semipalmatus the fin is
extended along the basal interspaces of only the four dorsal arms.
In the Cirroteuthis it extends between all the arms, and as far as
their attenuated extremities.* There are two layers of transverse
fibres in this web, the external of which arises from a white line
along the back part of the base of each arm, the internal from the
sides of the same arms between the attachments of the suckers. They
decussate one another as they pass from arm to arm in the middle of
the webs, and are included between two thin layers of radiating or
longitudinal fibres.

The internal surface of the arms is that which is specially modified
in the Dibranchiate Cephalopods, as in the Nautilus, for the pre-
hensile and tactile faculties ; but the structure is much more compli-
cated in the higher order. On this surface each arm supports a
single or double series or more numerous rows of acetabula or cir-
cular sucking cups : in the elongated pair of superadded tentacles of
the Decapods, the suckers are limited to the expanded extremities,
where they are generally aggregated in more numerous and irregular
rows. These tentacles serve to seize a prey which may be beyond the
reach of the ordinary arms, and also act as anchors to moor the Ce-
phalopod in some safe harbour during the agitations of a stormy sea.

Each muscular arm is perforated near the centre of its axis for the
lodgement of its nerve and artery, which are surrounded by a layer of
cellular tissue ; from the dense outer sheath of this cellular canal the
transverse fibres of the arm radiate to the periphery, intercepting
spaces containing the longitudinal fibres of the arm, the whole being
surrounded by two thin and distinct strata of fibres, of which the ex-
ternal is longitudinal, and the internal transverse.

The mechanical structure of the acetabulum may be favourably
studied in the Octopus, in which those organs are of large size, and
sessile. The circumference of the disc of the sucker is raised by a
tumid margin ; a series of slender folds of membrane, covering corre-
sponding fasciculi of muscular fibres, converge from the circumference
towards the centre of the sucker, where a circular aperture leads to a

' Eschriclit, Acta Acad. Nat. Cur. vol. xviii. p. 627.

346 LECTURE xxrv.

cavity which widens as it descends, and contains a soft caruncle, rising
from the bottom of the cavity like the piston of a syringe. When the
sucker is applied to any surface for the purpose of adhesion^ the piston,
which previously filled the cavity, is retracted, and a vacuum produced.

The complex irritable mechanism of all these suckers is under
the most complete control of the predatory Cephalopod. My friend
Mr. Broderip informs me, that he has attempted, with a hand-net
to catch an Octopus that was floating within sight with its long and
flexible arms entwined round a fish which it was tearing to pieces
with its sharp hawk's bill ; the Cephalopod allowed the net to approach
within a short distance of it, before it relinquished its prey, when in
an instant it relaxed its thousand suckers, exploded its inky ammu-
nition, and rapidly retreated under cover of the cloud which it had
occasioned, by rapid and vigorous strokes of its circular web.

The Cephalopods which frequent the more open seas, and which
have to contend with more agile and powerful fishes, have still more
complicated organs of prehension. In the Calamary the base of the
piston is enclosed in a horny hoop wuth a dentated margin. In the
Onychoteuthis the margin is produced into a long, curved, sharp-
pointed claw. These formidable weapons are sometimes clustered at
the expanded terminations of the tentacles, and in a few species are
arranged in a double alternate series along the whole internal surface
of the eight ordinary arms, as they were in the extinct Belemnite.

In connection with the uncinated acetabula at the extremities of the
long tentacula of this Onychoteuthis *, you may observe also a cluster
of small simple unarmed suckers at the base of the expanded part.
When these parts in each tentacle are applied to one another, they be-
come locked together, and the united strength of both the peduncles is
thereby more eff*ectually brought to bear upon any resisting object
which may have been grappled by the terminal hooks. This is a very
striking mechanical contrivance : human art has remotely imitated it
in the fabrication of the obstetrical forceps in which either blade can
be used separately, or by the interlocking of a temporary joint be
made to act in combination.

In the diminished number, increased size and progressive complica-
tion of the cephalic muscular appendages, and in their final modifica-
tion for combining with one another to produce a determinate action,
we trace the common order which regulates^the development of other
parts of the animal organisation. In our past review of the Inverte-
brata, we have witnessed this order in the appearance of the more
essential organs, as the stomach, the heart, the gills, the generative

* Prep. No. 166, D.

CEPHALOPODA. 347

organs ; we find it equally regulating the development of the peculiar
prehensile instruments of the Cephalopodic class.

At first very numerous, comparatively small and feeble, essen-
tially alike, the cephalic tentacles of the Nautilus strikingly illus-
trate the law of vegetative or irrelative repetition. Their primary
import is however plainly indicated by the direct derivation of their
central nerve from the cephalic ganglion ; and they present the
same complex plan of arrangement of their muscular fibres which
characterises the arms and tentacles of the dibranchiate Cepha-
lopods. The prehensile surface of the tentacula of the Nautilus is
made adhesive after the type of the simple laminated sucker of the
Remora ; the median longitudinal impression which partially divides
the lamella, may represent the complete interspace which separates
into two series, in the arms of most of the Dibranchiates, the more
complex suctorial appendages which are developed on their internal
surface : but at all events, the reduction of these arms in number,
their augmentation in size, and perfection as prehensile instruments
by the superadded complications, are phenomena which ordinarily
attend the march of development. The order of this progress
would be anomalously reversed if the tentacles of the Nautilus repre-
sented, as M. Valenciennes supposes, the caruncles of the acetabula,
and the hollow processes of the oral sheath the cavities of those
appendages of the arms of the Dibranchiata. According to the
French Malacologist, the anterior circumference of the head or oral
sheath in the Nautilus represents four of the eight arms developed
therefrom in the Dibranchiata^ and the two dorsal arms consist each
of two enormous acetabula, whose cavities are deepened into tubes, and
whose caruncles are produced into tentacula as highly organised in regard
to their nerves and muscles, as are the acetabuliferous arms themselves
in the higher orders. The four other arms of the Octopus are repre-
sented, according to M. Valenciennes, by the four groups of tentacula
which are included within the oral sheath in the Nautilus. Such is
not, however, the place of origin of any of the eight arms in the Di-
branchiata ; nor is it conformable with the general law of develop-
ment, that a prehensile organ consisting of two lar^e and highly
complicated acetabula in a low organised Cephalopod should support
two hundred smaller and more simple suckers in the higher organised
species.

Fasciculi of muscular fibres are continued from the ventral pair of
feet and the back part of the cranium to the muscular partition which
divides longitudinally the branchial cavity : other fibres descend to
join the muscular tunic enveloping the liver and oesophagus. In the
cuttle-fishes and calamaries the branchial septum is not developed.

348 LECTURE XXIV.

The respiratory tube or funnel is a complete muscular cylinder,
formed by an external longitudinal, and an internal transverse, layer
of fibres, with which are blended the insertions of the accessory
retractor muscles.

The analogues of the great muscles which attach the Nautilus to
its shell may be traced in the different genera of Dibranchiatay
diminishing in size as the internal shell becomes more and more
rudimentary. They arise in conjunction with the fibres of the fleshy
tunic of the liver from the posterior part of the cephalic cartilage ;
but, soon quitting these fibres, they extend downwards and outwards,
being perforated in their course by the great lateral nerve, and are
inserted into the epidermic capsule of the internal shell.

The thin shell of the Argonauta, which is external in regard to the
true mantle, but internal in relation to the brachial membranes which
formed it, is retained in its position chiefly by these membranes ; and
when they are, as they are capable of being, retracted into the cavity
of the shell, it adheres to the surface of the body by the adhesion of
contact only and its own elasticity, not by its attachment to any
muscular fibres : hence the animal commonly drops out of the shell
when dead.

The principal muscular fibres of the pallial fins extend, transversely to
the axis of the body, to the margins of the fins : they present the same
direction in the fossilised fins of the animal of the Belemnite. The
action of the powerful muscles in the terminal fins of the calamarics
must be aided in its effect upon the body by the elasticity of the in-
ternal pen or gladius. By these means they are enabled not only to
propel themselves forward in the sea, but they can strike the surface of
the water with such force as to raise themselves above it, and dart like
the flying fish for a short distance through the air. This is the
highest act of locomotion, the nearest approach to flight, which
any of the molluscous animals have presented.

We find associated with the varied and active powers of lo-
comotion just described, visual organs of large size and singular com-
plexity of structure. The whole surface of the body is highly sen-
sitive, with a concomitant development of the nervous centres, which
exhibit the highest conditions observable in the Invertebrate series of
animals.

The brain is inclosed in a cartilaginous cranium, together with a
portion of the oesophagus, from which it is separated by the mem-
brane analogous to the dura mater. Between that part of the fibrous
membrane which lines the cerebral cavity and the pia mater covering
the brain, there is an intervening space filled with a gelatinous
arachnoid tissue. In the cuttle-fish, the supra-oesophageal cerebral

CEPHALOPODA.

349

mass {fig. 135. «) consists prin-
cipally of a cordiform body,
superficially divided into two
lateral lobes by a median lon-
gitudinal furrow. From the
lower and lateral parts of this
body proceed the short and
broad optic nerves, w^hich con-
stitute the peduncles of the
large reniform optic ganglions
(6), and upon each peduncle
there is placed a small spherical
medullary tubercle : these tu-
bercles exist also in the Cala-
maries, but appear not to be
present in the Octopods.

From the inferior and ante-
rior parts of the supra> oeso-
phageal mass, a thick cord de-
scends on each side of the
oesophagus, unites with its fel-
low, and dilates below that tube
to form the anterior sub-oeso-
phageal ganglion, from which
the nerves of the feet and ten-
tacles arise. Two broader bands
descend from the supra-oeso-
phageal mass behind the pre-
cedingj and form, by a like enlargement and union, the posterior
oesophageal body, which blends laterally with the anterior one, and
forms with it a large mass with a central perforation. Four
short and slender chords, two of which (e) are continued from the
anterior apices of the optic lobes, and two from the anterior sub-
cesophageal lobes, converge forwards and unite to form a round
flattened ganglion (^), which is closely applied to the back part of
the fleshy mass of the mouth above the pharynx, from which are sent
off" the nerves to the different parts of the mouth. Two filaments
from the pharyngeal ganglion descend to join a pair of ganglions
below the mouth, analogous to the labial ganglions of the Nautilus.
The nerves of the arm (/,/) proceed from the anterior and inferior
sub-cesophageal ganglion, and correspond in number to the organs
which they supply, being eight in the Octopoda, and ten in the De-
capoda : the corresponding nerves are much more numerous in the

A'-

Nervous system. Sepia officinalis.

350 LECTURE XXIV.

Nautilus. In the Octopus, the brachial nerves pass along the inner
surface of the base of the arms before they penetrate them. As soon
as the acetabula begin to be developed, a series of closely approx-
imated ganglions are formed upon the brachial nerves, of which some
of the longitudinal fibres have been observed by Dr. Sharpey to pass
over the ganglions. Before the ganglionic enlargements commence,
each brachial nerve in the Octopus gives off two large branches, which
traverse the fleshy substance of the base of the arms to join the two
corresponding branches of the contiguous nerves which are thus as-
sociated together for consent of action by a nervous circle.

The infundibular nerves arise behind the origin of the brachial
ones. Posterior to these the small acoustic nerves are given ofi" from
the sub-oesophageal mass. The delicate motores oculi arise from the
upper part of the lateral connecting bands of the infra- and supra-ceso-
phageal masses, which may be compared with the crura cerebri, as the
nerves in question obviously answer to the third pair in the Vertebrata.
The nerves which correspond to those of the shell-muscles of the
Nautilus, form a single large pair (m, m), which arises from the pos-
terior and lateral angles of the sub-oesophageal mass, extend outwards
and backwards, perforate the shell-muscles, and form the large stel-
lated ganglions (n, n), from which the nerves of the mantle are prin-
cipally derived. In the Octopoda this may be described as the ter-
mination of the nerve ; but in the Decapoda, in which lateral fins are
superadded to the trunk, the great nerve previously divides into two
branches, of which the outer one expands into the ganglion, whilst
the inner branch, having been joined by one of the rays of the gan-
glion (o, o), pierces the fleshy substance of the mantle, and ends in a
diverging series of twigs appropriated to the muscles of the fin.

In proportion as the trunk of the Cephalopod is attenuated and
elongated, the pallial nerves become more parallel in their course,
more dorsal in their position, and more similar to a rudimental spinal
chord, of which the two lateral columns have retained their primitive
embryonic separation.

The two large visceral nerves (p) arise from the interspace of the
origin of the pallial pair ; after distributing filaments to the muscles of
the neck they descend parallel and close to one another behind the
vena cava, give off" the small filaments which constitute the plexus upon
that vein and around the oesophagus, then diverge from each other
towards the root of each gill, where they divide into three principal
branches : one of these dilates into an elongated ganglion {q) and
penetrates the fleshy stem of the branchia ; the second descends to
the generative organs ; the third passes to the middle or systemic
heart. The oesophageal plexus unites into a ganglion (r), attached

CEPHALOPODA. 351

to the parietes of the gizzard in the interspace between the pyloric
and cardiac orifices.

With respect to the parts of the brain in the Vertebrata, which are
represented by the cephalic nervous masses in the Dibranchiate
Cephalopods, we may regard the cordiform superior mass, which is
principally in communication and coexists with the large and complex
eyes, as the homologue of the optic lobes ; it cannot be the cere-
bellum, as Cuvier supposed, for that body never gives origin to any
nerve ; the cerebellum is also less constant than the optic lobes of
the Vertebrate brain, and is posterior to them in both position and
order of development.

The smaller supra-oesophageal mass, anterior to the optic lobes in
the Octopus and some other cephalopods, may represent an olfactory
lobe, or the rudiment of a true cerebrum. I have already indicated the
parts which seem to represent the crura of the cerebrum ; they unite
with that large subcesophageal nervous mass, which, since it gives
origin to the brachial nerves or the analogue of the fifth pair, to the
acoustic and respiratory nerves, and to those two large moto-sensory
columns which so obviously represent, by their structure, position and
distribution, the spinal chord of the Vertehrata^ must be regarded as
the representative of the medulla oblongata : it is obviously the part
of the nervous centre which is most intimately connected with the
vitality of the animal, and which is therefore here, as in the higher
animals, the deepest seated and best protected part of the nervous
system.

The integument is remarkable in several of the naked Cephalopods
for its irregular surface, which seems designed to increase its natural
sensibility ; in some, it is provided with flattened processes with den-
ticulated margins ; in others, it is beset with branched papillae ; in a
third with simple obtuse papillae ; in a fourth with pointed tubercles ;
all which projections may serve to warn the animal of the nature of
the surfaces with which it may come into contact. The margins of the
acetabula and the attenuated flexile extremities of the arms which
support them doubtless possess a delicate sense of touch. The
fringed circular lip presents another example of the dermal covering
modified to be the seat of this sensation.

The tongue is as highly developed for the exercise of the sense
of taste in the dibranchiate Cephalopods as in the Nautilus.

The external circular lip may probably be the seat of the sense of
smell ; it is the part which is most analogous in position and struc-
ture to the olfactory laminae in the Nautilus. This sense has been
attributed to the Cephalopods by all naturalists who have observed
their habits from Aristotle to Cuvier. It appears that the ancient

352 LECTURE XXIV.

Greek fisliermen were in the habit of attaching strong-scented herbs
to their baits to deter the cuttle-fishes from coming to devour
them.

The organ of hearing consists of two vestibular cavities, excavated
in the thick and dense part of the cartilaginous cranium which sup-
ports the suboesophageal ganglions. In the cuttle-fish several obtuse
elastic processes project from the inner surface of the cavity, which
contains a delicate sacculus and otolithe. The acoustic nerve is
spread over the sacculus, and is impressed by the movements of
the otolithes, which respond to sonorous vibrations, which may be
strong enough to affect the body generally. In the Octopus the
vestibules are nearly spherical with a smooth internal surface ; the
otolithe is hemispherical ; in the Eledone it is shaped like the shell
of a limpet, with the apex rounded and curved backward. In all the
Cephalopods the otolithes consist of carbonate of lime.

The orbit in the cuttle-fish is formed posteriorly by a thick
cartilaginous cup, and is completed anteriorly by a dense white
fibrous dermal membrane, which becomes transparent at the anterior
part of the globe, and forms the cornea. The cornea and the fibrous
tunic are lined by a thin serous membrane, which is reflected over
the anterior part of the sclerotica, and through its anterior aperture
(to which the cornea does not adhere), like the membrane of the
aqueous humour, and is finally continued into the groove of the
crystalline lens.

The space between the eyeball and its capsule, thus circumscribed,
is filled with an aqueous humour, by w^hich the cornea is separated
from the eyeball, and kept tense. The outer tunic of the proper
eyeball is a fibrous membrane covered by the aponeurotic expansion
of the muscles of the eye, and with an anterior aperture which is
closed by the crystalline lens. Within the fibrous tunic there is a
thin cartilaginous coat perforated posteriorly by the numerous
fibrils from the optic ganglion. The layer of fibrous membrane is
continued from the anterior margin along with the outer fibrous
layer to form the pupillary aperture, Avhich is encroached upon by a
bilobed process analogous to the curtain, which depends from the iris
of the ray. The cartilaginous sclerotic is lined by a thick expansion
of the nervous fibres given ofi" from the optic ganglion. These fibres
are sent off" from the outer surface of the ganglion, which presents a
pulpy texture in its centre. They are grouped into flattened bundles,
which decussate each other, as observed by Dr. Power, before
perforating the cartilaginous sclerotica, and, after expanding into the
retina, extend towards the groove of the crystalline lens, and, being
joined by a thin membrane from the anterior margin of the car-

CEPHALOPODA.

353

tilaginous sclerotic, it forms a ciliary plicated zone, which penetrates
the groove of the crystalline lens.

The inner surface of the retina is covered by a layer of dark
pigment, which is penetrated by the papillae of the retina. The
vitreous humour has a distinct and strong hyaloid coat. The crys-
talline lens is of large size, and consists of two distinct parts ; the
anterior or smaller moiety being the segment of a larger sphere, and
the posterior that of a smaller sphere : they are separated by delicate
transparent membranes continued from the ciliary body. The lens
presents the same denticulated fibrous structure arranged in con-
centric laminae, as in the higher animals.

The large optic ganglion is imbedded in a white lobular sub-
stance, which defends it from the pressure of the muscles of the eye-
ball. These consist of three straight muscles and one oblique, which
take their origin from the orbital cartilages, and expand upon the
sclerotic tunic of the eyeball. 'J'he cornea of the cuttle-fish is per-
forated by a minute hole near the inner or anterior margin. In the
Octopus the corresiDonding aperture is somewhat larger, and situate
more in the axis of vision. In the Calamaries the corneal aperture
is still larger, of a vertically oblong form, and the capsule of the
crystalline lens, which projects through the sclerotic aperture, is
immediately exposed to the sea water.

The dibranchiate Cephalopods are, without exception, predatory and

carnivorous animals. We have seen
that they are endowed with for-
midable organs for seizing and over-
coming the struggles of a living
prey, and their strong sharp hooked
jaws are well adapted for de-
stroying and lacerating them when
caught. The jaws {fig. 136. k, I)
are sheathed upon a firm fleshy sub-
stance, the fibres of which are so
attached to the base of the mandibles
as to open them ; their closure is
effected by fasciculi of muscular
fibres which surround them exter«
nally.

The tongue is partially covered
with a horny plate beset with re-
curved spines, which must assist in
the further comminution and deglu-
tition of the food. The fauces are also provided with spinigerous folds

A A

Octopus.

354 LECTURE XXIV.

of membrane. In some of the Calamaries, in which the superior sali-
vary glands penetrate the folds, the ducts open upon the inner surface,
as in the Nautilus. In the Octopus the anterior or upper salivary
glands are on the outside of the buccal mass. In most of the Dibran-
chiata a second and larger pair of salivary glands is situated on each
side of the oesophagus, at the commencement of the abdominal or
hepatic cavity ; their ducts unite to terminate below the tongue in the
concavity of the lower mandible.

The peritoneal membrane is divided and disposed as in the Nau-
tilus, in order to form special receptacles for the different viscera.
The oesophagus is narrower than in the Nautilus, and provided
with longitudinal plicae : it dilates soon after having passed through
the cranium into a long ingluvies, forming a large cul-de-sac at
its commencement in both the Octopus and Argonaut ; but in the
Decapods it continues narrow and of uniform breadth to the stomach.
This cavity (A) is an elongated sac, presenting, in the disposition of
its muscular fibres, in the jDroximity of the cardiac and pyloric orifices,
and in the thickness of the epithelial lining, the usual char.acters of
the gizzard. The intestine, at a short distance from the pylorus, com-
municates with a glandular and laminated sac (q) analogous to that
in the Nautilus, and presenting a similar globular form in the Rossia
and Loligopsis ; but elongated and spirally convoluted in the Sepia
and Loligo. It receives the biliary secretion between two broad
lamellee, as in the Nautilus. The intestine is very short in all the
Dibranchiata. In the Octopus it is bent upon itself (r), as in the
Nautilus ; but in the Sepia and Loligo it is continued forwards in a
straight line, from the stomach to the vent. Its internal membrane
is longitudinally folded, but is smooth at the short tract beyond the
entry of the duct of the ink-bag ; its termination is constricted either
by the muscular fibres of the branchial septum, or by those which
connect together the pillars of the funnel. In the Decapods provided
with fins for swimming forwards, the anus can be closed by tri-
angular fleshy valves ; and in some species these are modified into
the form of antennal filaments.

The liver (a?) is of large size in the Dibranchiata, but of more
simple form than in the Nautilus. In the Sepia it is divided into
two lateral lobes, which are notched at the upper extremity ; in the
Onychoteuthis it is a simple, elongated, compressed lobe with un-
divided extremities: in the Octopus it forms a single oval mass,
flattened anteriorly : in the Eledone it is spherical, corresponding with
the ventricose visceral sac. In the two latter genera the ink-bag {d)
is enclosed within the capsule of the liver, and was naturally mistaken
for the gall-bladder by some of the early anatomists of these ^ol-

CEPHALOPODA.

355

iusca ; but in the Argonaut and in all the Decapoda, it manifests its
distinct function by its separate position. The liver issurrounded by
a smooth capsule, and is not subdivided externally into lobules, as in
the Nautilus and lower MoUusca. The biliary ducts in the Octopoda
are simple canals, which unite and terminate by a common orifice,
in the pancreatic sac. In the Decapoda they receive the ducts of
numerous clusters of caecal appendages beyond the smooth part of
the liver.

The ink-bag consists of tough white fibrous texture, the outer sur-
face of which is coated by a thin silvery or nacreous layer : its inner
surface presents a fine spongy glandular texture. It presents a trilobate
form in the Sepiola, and an oblong pyriform shape in the Sepia and
Loligo. It is a very active organ, and its inky secretion can be re-
produced with great activity. The tint of the secretion varies in dif-
ferent species, as is exemplified by the Italian pigment called ' sepia,'
and the Chinese one, called ' Indian ink.' It is of a very indestructible
nature, as is exemplified by its frequent preservation in a fossil state
in both the extinct Calamaries and the Belemnites. It is affirmed
by some chemists to contain a peculiar animal principle, which Vizio
has termed ' melanine.'

Many of the Cephalopods possess the power of emitting a luminous
secretion. All of them are nocturnal and social animals, and are
readily attracted by bright metallic substances.

Prior to the dissection of the Pearly Nautilus, the Cephalopods
■were regarded as having three distinct hearts ; but two of these, which
are appropriated to the branchial circulation, are peculiar to the higher

order, and are perhaps
the main-spring of their
superior muscular ener-
gies.

In the Dibranchiata
the venous blood returns
from each arm along
its lateral and posterior
parts by two veins, which
severally unite at the
base of the arm with the
opposite vein of the ad-
joining arm, the whole
being ultimately convey-
ed to an irregular circular
sinus, which is continued
Sepia officinalis. between the head and

A A 2

356 LECTURE XXIV.

the funnel into the great anterior cava (^^. 137. a). In the Octopus
this vessel is provided with two semilunar valves at its commencement.
At its entrance into the pericardium it usually receives two large
visceral veins, and it divides into two branches {g, g), continued
downwards and outwards to the branchial hearts at the base of
each lateral gill : previously to communicating with these it dilates
into asinus, which also receives the venous blood from the sides of the
mantle. The two divisions of the vena cava, and also the visceral
veins (b, b), after having entered the pericardium, are furnished with
clusters of spongy or glandular follicles, which open into these veins by
conspicuous foramina. The follicles vary in form in different genera;
in the Eledotie they are elongated and pyriform : in the Argonauta and
Octopus they are shorter, and arranged in distinct clusters : in the Loligo
they are represented by a spongy thickening of the tunics of the veins :
in the Sepia the secerning appendages are more elongated, but are very
numerous, close-set, and of an irregular form, giving afloccular character
both to the great divisions of the vena cava and to those parts of the
visceral veins which are contained in the pericardial or great venous
cavity. The special compartments, into which these glandular ajj-
pendages to the veins are lodged, communicate with the respiratory
cavity by two papillary orifices, situated near the base of the gills.
As the kidneys derive their peculiar excretion from venous blood in
the lower vertebrated animal, Prof. Mayer's supposition * that the
venous follicles of the Cephalopods are analogous organs, is by no
means an improbable one. They may serve in a secondary degree
as temporary reservoirs of the venous blood when it is impeded in
its course thi'ough the gills ; and, as the venous follicles are endowed
with a peristaltic motion, they may regulate the quantity of blood
transmitted to the gills.

The branchial circulation is, however, expressly provided with a
muscular ventricle (fig. 136. s) in the Dibranchiate Cephalopods, one
of these ventricles {fig- 137. h) being situated at the base of each
gill. The regurgitation of the blood into the glandular veins is pro-
vided against by the interposition of the two semilunar valves at the
entry of the ventricle. In the Decapoda and in the Argonaut, each
branchial ventricle has a fleshy appendage {k) attached to its lowest
surface.

A single branchial vein which dilates into a small sinus (fig.
137. /) returns the blood to a single median systemic heart, which is
rounded in the Octopods, lozenge. shaped in the Calamaries, and fusi-
form, but bent upon itself, in the Sepia (fig. 137. m) Sepioteuthis, and

* Analekten fur Vergleichenden Anatornie, 4to, 1835.

CEPHALOPODA. 357

Sepiola. It sends off two aortae, as in the Nautilus, the larger or
posterior aorta being provided with a muscular bulb, and with two
semicircular valves at its origin. The distribution of the large aorta
very closely resembles that of the Nautilus. The vascular ring which
encircles the oesophagus typifies the branchial arches in the Verte-
brate animal ; but it supplies the head and all its complex radiating
appendages.

The branchiae {Jig. 136. t. Jig. 137. i) are two in number, as the name
of the order indicates. They are concealed, as in the Nautilus, by
the mantle, which extends in front of the other viscera to form the
branchial chamber: a distinct muscular tube projects from its out-
let. The rectum and the generative organs open into the branchial
chamber at the base of the funnel, manifesting the same relation of
the breathing organs to the termination of the alimentary canal, which
characterises the lower orders of the Mollusca. Each gill consists,
as in the Nautilus, of a number of triangular vascular laminae, ex-
tending transversely from either side of the fleshy stem, and de-
creasing in size to the extremity of the gill; each plate is composed
of smaller transverse laminag, which are themselves similarly sub-
divided, the entire gill presenting the tripinnate structure, which af-
fords the most extensive surface for the minute subdivision of the
blood-vessels. In the LoUgopsis each gill has twenty-four pairs of
plates: m the Sepia, thirty-six pairs ; in the Loligo sagittata, sixty
pairs. The stem of the gill is not only attached by its base, but by a
thin fibrous membrane through nearly its whole length to the mantle.

The mechanical part of the respiratory act is performed by the
muscular actions of the mantle and funnel, the gills not being pro-
vided with vibratile cilia, as in many of the inferior Mollusca. The
w^ater is admitted into the branchial cavity at the anterior aperture of
the mantle, outside the base of the funnel. Two large valvular folds
of fibrous membrane, which are concave towards the respiratory
cavity, prevent the currents from escaping by this entry : they are,
therefore, propelled by the whole force of the contraction of the
muscular mouth through the cavity of the funnel, the base of which
is articulated, in most of the Cephalopods, by lateral joints, with the
sides of the anterior aperture of the mantle.

At first sight it might seem that the Cephalopods which had bui
two gills were less efficiently provided with the means of respiration
than those which have four ; but increased number, irrespective of
correlative structure in an organ of the animal body, is ever a mark
of its inferiority; and the four branchiae of the Nautilus forcibly
illustrate the true character of vegetative repetition, when contrasted
with the two gills of the cuttle-fish in connection with their super^

A A 3

358 LECTURE XXIV.

added ventricles. With this mechanism for the vigorous propnlsion
of the venous blood through the oxygenating organs, they acquire,
in the Dibranchiate Cephalopods, a perfection of structure unknown
in the rest of the Invertebrata, but always present in the Vertebrated
classes.

The male Dihranchiata are always fewer, and generally smaller,
than the females ; the latter sex alone has hitherto been recognised
in the genus Argonauta, and some suspect the brachial membranes
and the shell to be sexual distinctions. In the common Loligo, the
gladius of the male is one fourth shorter, but is broader than that of
the female.

The male organs consist of a testis, a vas deferens, a vesicula
seminalis, a prostate, the sac of the spermatophora, and the penis.

The testis is situated in a particular compartment of the peritoneum
at the bottom of the visceral cavity : it consists of a membranous
pouch, to one part of the inner surface of which are attached a
number of slender branched tubuli, diverging, dichotomising, and
terminating in blind extremities : the tubuli swell at the breeding
season, burst, and discharge an opaque white fluid, crowded with
spermatozoa, into the cavity of the sac, whence it escapes by a con-
tracted orifice into the slender and convoluted vas deferens, where
the fluid is moulded, by the addition of a mucous secretion, into a
cylindrical coherent mass. In this state it is ti^ansmilted to a wider
glandular canal, with fibrous parietes and a cellular cavity in the
Octopus, and encroached u23on, in the Sepia, by a plicated production
of the lining membrane : this division of the eflPerent part of the
male apparatus is analogous to the glandular part of the oviduct in
the female : here the spermatozoa are enclosed in filamentary sheath*
of albuminous matter, of a definite form, according to the species of
Cephalopod. The anterior extremity of this contractile vesicula com-
municates, in the Octopus, with a wide, bent, csecal tube (prostate),
with thick glandular parietes, and having the form of a simple pouch in
the Sepia, from which a short and wide duct leads to a longer and
larger pyriform pouchy with thinner walls, containing the moving
filaments of Needham, and from which the short muscular penis is
continued. The prostate, in the Sepiola, communicates by a long
and slender duct with the vesicula seminalis.

The moving filaments in the terminal pouch are packets or
capsules of spermatozoa and sperm-fluid, with a peculiar associated
mechanism. They form one of the most remarkable peculiarities of
the Cephalopoda, and have been regarded as parasitic worms, under
the names of Echinorhynchus, Scolex dihothrius, Needhamia expul-
satoria, kc, by diff'erent comparative physiologists : they have been
aptly denominated ' spermatophora' by Dr. Milne Edwards.

CEPHALOPODA. 359

In the Octopus they are from six to eight lines in length, slightly
enlarged at one extremity. Their outer tunic or capsule is elastic
and transparent : this contains an elongated sac, occupying the
larger extremity of the sheath, and filled with the minute elavate
spermatozoa. This sperm-sac communicates by a short narrow canal
or isthmus, with a second narrower or elongated sac, with highly
elastic parietes. From this sound sac a spiral filament is continued
to the small extremity of the outer sheath. In the Cuttle-fish, the
isthmus connecting the sperm-sac with the ejaculatory sac is longer,
and the coils of the spiral membrane are closer and more numerous.
The spermatophora, or Needhamian filaments of the Calamary are
remarkable for the superior size and length of the internal sac con-
taining the spermatozoa.

Under every modification, the analogy of the apparatus which
forms the receptacle of the essential particles of the fertilising fluid,
with the nidamental sacs containing the ova in the opposite sex, is
very obvious, and this explanation of the nature of the moving
filaments, which has been illustrated with much accurate detail by
Drs. Peters and Edwards, is, without doubt, the correct view. The
movements of the spermatophora, when liberated from the sac, are
truly remarkable ; the smaller extremity of the outer capsule, to
which the spiral spring is attached, protrudes by a kind of inversion,
and the inner spermatic sac is drawn forwards ; the action is re-
peated until the ejaculatory sac is extended from the sheath, when
there is a slight cessation of movement. It then recommences ; the
sperm-sac is compressed and protruded farther; the isthmus gives
way, and the spermatozoa are violently expelled, both outwards and
into the cavity of the external sheath. The efficient cause of the
movements appears to be a combination of the contractility of the
external sheath and sperm receptacle, the elasticity of the spiral
membrane, and the phenomena of endosmosis. The final intention
of the superaddition of protecting sheaths for the semen, like those
for the ova, appears to relate to the safe conveyance of the sperma-
tozoa to the ova of the female, there being apparently no true intro-
mission in the Cephalopoda ; the peculiar mechanism of the sperm-
receptacles insures their rupture and the dispersion of their contents
after their brief transit through the sea water.

The female organs consist in the Dibranchiate Cephalopods, as in
the Nautilus, of ovarium, oviduct, and superadded nidamental glands,
but with several modifications in the efferent part of the apparatus.
The ovary is always single, and the ovisacs, characterised by their
elliptical form and reticulate parietes, are attached to one part of its
cavity, as in the Nautilus. In the Cuttle-fish there is a single oviduct,

A A 4

360 LECTUKE XXIV,

Avith a glandular laminated outlet ; and there are two distinct laminated
nidamental glands on each side of its termination. In the Octopoda
there are two oviducts, which in the Octopus and Eledone are each
provided with a special glandular enlargement about the middle of
their course : but there are no detached nidamental glands. In the
Loligo there are two distinct convoluted oviducts, and two separate
nidamental glands. These glands in the Cuttle-fish rest upon a soft
parenchymatous body, of a bright orange colour : the corresponding
part is rose-coloured in the Sepiola: it is double in the Rossia and
the Calamaries : these bodies have no ducts, and appear to be the
analogues of the suprarenal bodies in the vertebrate animals.

The ova when received in the membranous part of the oviduct,
consist of a deep yellow vitellus, enclosed in a delicate vitelline mem-
brane, and protected by a thin smooth shining chorion : they receive
additional layers of a thick albuminous matter from the gland of the
oviduct, which may be compared to the shell-secreting cavity in the
oviduct of the fowl. The ova are connected together in characteristic
clusters by the secretion of the superadded nidamental glands when
these are present.

In the Argonaut the minute ova are appended by long filamentary
stalks to the cavity of the involuted spire of the shell where they are
hatched. The ova of the Calamary are enclosed in long gelatinous
cylindrical sheaths, and offer a close analogy to the spermatophora in
the male. The ova of the Sepioteuthis are likewise enclosed in cylin-
drical sheaths ; but these are shorter^ and contain fewer ova, than in the
Loligo. The eggs of the Cuttle-fish are of comparatively large size,
of an oval form, attenuated at the extremities, and each enveloped in
its proper horny covering, -which is prolonged into a pedicle at one
extremity, and attached by it to some foreign body : numbers of these
ova are generally found clustered together, and they have commonly
received the name of sea-grapes.

The early stages in the development of the Cephalopodous Mollusk
appear not to have been hitherto observed. The head can very soon
138 ^iffrmtin-^ ^^ distinguished by the pigment of the rudi-

mental eyes : the branchiae at their first ap-
pearance project on each side of the pedicle
of the large yolk-bag, from the anterior and
lateral part of the unclosed abdomen, and
the embryo Cuttle-fish at this period mani-
fests the infero-branchiate type. The visceral
sac is progressively enclosed by the advance-
ment of the pallial walls from behind forwards ;
E^ryo Sepia. the pcdiclc of the yolk-bag {jig. 138. c) pro-

CEPHALOPODA. 361

gressively contracting, and being pushed, as it were, towards the head ;
the short intestine is developed from the bottom of the stomach (b),
and passes straight forward to the base of the projecting funnel. The
arms grow around the mouth (a) and the vitelline duct, which is
continued anterior to the mouth, parallel to the oesophagus, and
gradually dilates (J) as it descends into the stomach. The original con-
nection of the yolk-bag is in part retained or indicated in the Octopus
by the anterior caecal production of the crop. At the later periods of
development the respiratory movements are vigorously performed by the
alternate dilatation and contraction of the mantle and by a corresponding
erection and depression of the funnel : the ink-bag (e) is now con-
spicuous by the colour of its contents, which are sufficient to blacken
a considerable quantity of water, and the little Cephalopod is thus
provided with the means of concealing itself from any enemy that
might be prepared to devour it upon its emergence from the defensive
covering of the ovum. At the period of exclusion five of the layers
of the dorsal shell (/) of the young cuttle-fish have been formed ;
but, except the nucleus, which is calcified, they are horny and trans-
parent. The lateral fins are not merely developed, but are broader
than in the mature animal ; and the cephalic arms are furnished with
a web ; so that the young Sepia is enabled to swim either forwards or
backwards, and its eyes have acquired the requisite development to
warn it of an approaching enemy, or direct its course to its appro-
priate food.

And now, Mr. President, I perceive that the hour of lecture has
drav/n to its close, and with it the period allotted for the annual ex-
position in this theatre of the physiological treasures of the Hunterian '
Museum. I should do injustice to my feelings were I, Gentlemen, to
suppress the expression of the great gratification which your untiring
attendance at these lectures has afforded me. This encouragement,
knowing that the lectures would commence with the lowest and most
minute forms of animal life, and be exclusively devoted to the Inver-
tebrated classes, I had not ventured to anticipate from an audience,
including many members who are actively engaged and eminent in
the practice of an arduous profession.

For there is so small a part of the multifarious and diversified
details of the anatomy and physiology of the Invertebrata, from which
the practical Surgeon can directly profit : they seem so remotely
connected with human physiology : the animals themselves are so
different in form, in powers, in modes of life, from those which
more obviously attract the interest of the anatomical Teacher.

We learn, indeed, with little surprise, that the import of the dissec-

362 LECTURE XXIV.

tioiis of the Invertebrate animals, by the busy care-worn Surgeon
who, in the last century, j^repared the most instructive illustrations of
our present lectures, were not understood, and that these occupations
of Hunter were regarded by some of his contemporaries as a kind
of laborious trifling. But the question of " cui bono ? " which might
then be pardonable, is surely inexcusable at the present day, when the
relations of Surgery as a science to Physiology, and the dependence of
Physiology upon Comparative Anatomy ought to be better understood.
I would not, however, desire a more satisfactory answer to any re-
maining scepticism as to the necessity or importance of the dissections
of the lower organised animals, than your reception of the present
course of lectures ; and I trust that a very brief retrospect of some of
the deductions that have been obtained from the details to which you
have patiently listened, will suffice to demonstrate their value to all
who are interested in the progress of physiological science.

The Invertebrated classes include the most numerous and diversified
forms of the Animal Kingdom. At the very beginning of our
inquiries into their physiology we are impressed with their important
relations to the maintenance of life and organisation on this planet,
and their influence in altering and augmenting the crust of the earth
itself, relations of which the physiologist conversant only with the
Vertebrated animals must have remained ignorant. At our first
entrance, and by the lowest portal, into the vast and intricate repo-
sitories of the animal mechanisms, we are at once introduced to the phe-
nomena of spontaneous fission and ciliary motion, of the generality and
importance of which in the animal economy each day seems to bring
fresh proof, but which are most conspicuously manifested in the Monads.

The physiologist must have remained in ignorance of the most
instructive modifications and combinations of the principal organs of
the animal frame, if the researches of the Comparative Anatomist had
been confined to the Vertebrated animals, or to those which are con-
structed on the same general type as ourselves. Without a much
deeper investigation, we never could have understood the relative
importance of the diff'erent organs, or have become acquainted with
their most striking analogies.

Only in the Invertebrated classes do we find examples in which
the lungs, like the liver, are supplied by the ramifications of the
trunk of a vein without the interposition of a heart. Only in the
lowest of the Invertebrate animals could we have found the office
of the lung performed by a vascular portion of the integument;
and the Invertebrata alone could have furnished us with examples
of the progressive modifications of this portion of the vascular
skin, by which the breathing organ is at length definitely developed.

CEPHALOPODA. 363

But why do I cite the respiratory system ? The earliest and most
instructive forms of almost every organ, as it is permanently arrested
in its development and adapted to the exigencies of the mature
animal, must be sought for amongst the Invertebrata.

These animals alone furnish us examples of the circulation of the
blood without a heart, and of a circulation aided by the hundred-
fold repetition of the propelling reservoir in the same individual. In
these alone we meet with the singular condition of the circulating
fluid meandering back to the heart through diffused venous lakes,
instead of cylindrical canals. Only the low organised Invertebrate
animal could have revealed to us the actual existence in nature of a
condition of the blood's motion, once erroneously held to be uni-
versal, viz. its flux and reflux in the same vessels, from trunks to
branches and from branches to trunks, to and from the heart.*
Could this remarkable exceptional case of the minute Ascidian have
been shown to the antagonist of Harvey^ how triumphantly he
might have appealed to the evidence of the senses as demonstrative
of the doctrine which Aristotle had taught and illustrated by the
analogy of the tides of Euripus !

In the Invertebrate series we can contemplate the most simple and
essential condition of the nervous system, — a ganglion with ra-
diated internuntiate chords, a centre for the reception and trans-
mission of stimuli. In this series we see such centres multiplied and
set apart for diff'erent segments, or for different organs of the body.
Of such arrangements, the anatomist of the Vertebrata exclusively
could have formed no adequate conception. And not only are the
conditions for the performance of the most essential function of the
nervous system, — viz. the working of the muscular machinery agreeably
with impressions received from external objects, independently of
any consciousness of such changes, or of any choice and volition in
the mode of remedying or avoiding them, — most plainly set forth in
the Invertebrate types of the nervous system ; but they afford the
best subjects for illustrating that primary function by experiment.
No vertebrate animal, for example, could have yielded such striking
results as have been detailed in the experiments on the Mantis. t

The Invertebrate animals reveal the constant relation of the brain
to a position above or behind the alimentary tract, and demonstrate
that organs of special sense govern the existence of the supra-
oesophageal nervous mass, and that its increase of bulk is in the direct
ratio of their increase in number or complexity.

The relation of the physical defence of an animal by shells or

* Lecture XX. Tunicata, p. 27:3. f Lecture XVI, Insecta, p. 207.

364 LECTURE XXIV.

crusts to the low condition of the sentient system, is most strikingly
manifested in the Invertebrate series, and could be but feebly dis-
cerned in the higher animals, none of which exhibit the external or
dermal skeleton modified to encase the limbs and form the levers
and fulcra of the moving powers. The defence of the crab and
oyster, by dense and impenetrable armour as a compensation for
their lack of intelligence and defective powers of action, reminds
one of the condition of the soldier in the early and ruder states of
the art of war.

If the structure and functions of the human mechanism had been
illustrated only by comparison with those of other Vertebrata, the
physiologist would have been acquainted with only one leading
modification of the generative system in the Animal Kingdom,
namely, the dioecious or bisexual. The analogy between animals
and plants in the modes of continuing the species is fully illustrated
only by the Invertebrata. Here the anatomist finds the self-sufficing
combination of fertilising and productive organs in the same indi-
vidual, as in most flowers. Other Invertebrata present the still more
remarkable combination of male and female parts arranged for
reciprocal union. The closer and more remarkable analogy with
the vegetable kingdom offered by that peculiar modification of the ge-
nerative system, in which we found the oviduct and vulva exclusively
destined for the transmission of the moving particles of the fertilising
fluid, the fertilised ova escaping into the abdomen by dehiscence of
the ovarium, so that extra-uterine gestation was a natural and con-
stant phenomenon, was demonstrated by dissection of the earthworm.

But the diversified structures of the Invertebrate animals not only
teach ,us the most remarkable and instructive modifications and
correllations of individual organs and systems, but lead to an irtsight
into, and can alone furnish the demonstrations of, the most important
generalisations in zootomical science.

Of that which I have termed ' the law of vegetative or irrelative
repetition,' by which is meant the multiplication of organs performing
the same function, and not related to each other by combination
of powers for the performance of a higher function, the Invertebrata
afi*ord the most numerous and striking illustrations.

Almost every organ of the body illustrates this vegetative con-
dition at its first appearance in the Animal Kingdom. A stomach
or assimilative sac is the most general characteristic of an animal.
Such sacs are developed in great numbers in the body of the Poly-
gastrian, but each sac performs the same share of the digestive
function, irrespective of the rest. The case is very different in the
ruminant animal, in which each of the four stomachs has its appro-

CEPHALOrODA. 305

priate office, and all combine together to produce a more efficient
act of digestion.

The organs of generation, the next essential parts of the mere
animal, when first definitely introduced with their characteristic
complications in the low organised Entozoa, illustrate more forcibly
the law of irrelative repetition.

We trace the definite development of the heart and gi'.ls in the
Anellida, in some species of which both organs are irrelatively
repeated above a hundred times. And when these, like most of the
vegetative orgar.s assume a more concentrated form in the Molluscous
series, we perceive in the structure and relations of the two auricles of
the bivalve as compared with the single auricle of the univalve, and of
the twenty tufted gills of the Phyllidia, or of the four gills of the
Nautilus, as compared with the two branchiae with their perfect cir-
culation in the Sepia, that plurality is but a sign of inferiority of
condition.

When locomotive and prehensile appendages first make their
appearance in free animals, they are simple, soft, and unjointed, but
they are developed by hundreds, as in the Asterias and Echinus : they
manifest the principle of vegetative repetition to a remarkable extent
when they are developed into symmetrical pairs of setigerous tubercles
in the Anellides, and even when they first appear as jointed limbs in
the Myriapoda: but as they become progressively perfected, varied, and
specialised, they are reduced to ten in Crustacea, to eight in Arachnida,
and to six in Insecta. We have just seen that the same law prevails in
the introduction of the analogous cephalic organs of locomotion and
prehension in the Mollusca. It is beautifully illustrated in the in-
troduction of the organ of vision into the animal kingdom.

The numerous ganglions, nerves, and muscles, which the vegetative
succession of the segments of the body and their locomotive appen-
dages in the Articulata calls forth, have sometimes been adduced as
invalidating the claims of the Vertebrata to be regarded as of higher
or more complex organisation ; but when the law of irrelative repe-
tition is rightly understood, the multiplication of similar parts for the
repetition of the same actions is at once appreciated as essentially
the more simple, as well as the inferior condition to the assemblage of
less numerous parts in the same body with different offices, and \vith
prospective arrangements that enable them to combine their different
powers for definite ends.

The lowest Invertebrata resemble locomotive cells : they propagate
by spontaneous fission and grow by assimilation ; sometimes they
exhibit their geometrically multiplied divisions to a certain extent
within a common capsule. The earliest phenomena in the develop-

366 LECTURE XXIV.

ment of the Mammiferous ovum most closely resemble these in the
Gonium and Volvox. Like phenomena have been observed in the
vitelline germ of the frog and the fish. But the universality of the
phenomena of spontaneous division, of the fissiparous procreation of
nucleatedcells, and of their growth by assimilation and coalescence round
definite centres, as the properties of the primordial germ in all animals
which produce the most conspicuous changes in the yolk, has been
mainly established by collecting the observations that have been made
upon the developm.ent of the embryo in the diff'erent classes of Inverte-
brata, and by the comparison of these with the analogous phenomena
observed in the development of the Vertebrate Animal, and which
we may conclude to characterise the first steps in tlie formation of
the human embryo.

And since later observations have established what I first observed,
and suggested to be a general property of the blood-corpuscle, — viz.
its power of spontaneous subdivision into smaller vesicles*, it is
highly probable that the preliminary steps to its conversion into a
tissue are the same as those of the nucleated cell which constitutes the
germ of the entire animal; and the proposition that the phenomena of
spontaneous fission, of which the Monads offer the most conspicuous
examples, are the most universal and important in the operations of
the living animal, ceases to wear the aspect of exaggeration.

It is however certain that the most extraordinary consequences of
the fissiparous property of the nucleated cell are manifested in the
Invertebrate series of animals, of which generation without fecunda-
tion of the procreating individual is an example. This phenomenon,
which has so much astonished and perplexed physiologists, as mani-
fested in the Aphides, becomes perfectly intelligible and reducible to
the general law.

The Monad divides itself before our eyes, constituting two, then
four, next eight individuals, and so on. The impregnated germinal
vesicle, which the Monad permanently represents in nature, propa-
gates, in like manner, by spontaneous fission and assimilation, a number
of impregnated cells like itself. Most of these cells are metamor-
phosed into the tissues of the growing embryo, but not necessarily all.
Certain nucleated cells, the progeny of the primordial one, and in-
heriting its powers, may become, without further stimulus, the centres
of development of processes like those which have built up the body
that contains them : they may bud forth from the stem of the Hydra,
and form new individuals by the process of gemmation ; they may
bud forth, in like manner, from the larval polype of the Medusa, which

* Medical Gazette, November 13. 1839. Dr. Martin Barry's Paper in Philos.
Transactions, 1840.

CEPHALOPODA. 367

thereby procreates in its immature, and, as it seems, virgin state, like
the wingless larvae of the summer Aphides ; they may enter the
unimpregnated oviducts of these insects, and be there developed in
the manner which has already been described.*

Did time permit, I might easily multiply the instances from the
Invertebrate organisations, which bear directly on the establishment of
the most important general laws in physiology. I shall conclude by
adverting to one which is alike interesting to the anatomist and natu-
ralist, and which has exercised the powers of the most exalted intellects
of the present age. To the disquisitions and discussions in which
Goethe, Oken, Cuvier, and GeofFroy have taken part, the doctrines
of Morphology and Unity of Organisation owe their existence.

Some of the medical acquaintances of John Hunter, who, we are
told, complacently apostrophised his pursuits, in the language of pity,
when they found him dissecting a snail, a bee, or a worm, little
dreamt of the expanded views of the animal organisation at which he
was obtaining glimpses through those narrow casements. It would
seem that Hunter himself was oppressed with the grandeur of the
prospect, with the extent of the generalisations which his investiga-
tions of the lower animals, and of the embryonic forms of the
higher ones, were forcing upon his reflective mind, if we may judge
from his struggles to express ideas, at that period so novel and so
vast, and to which he could but give imperfect utterance. " If we
were capable," he says, " of following the progress of increase of
the number of the parts of the most perfect animal, as they first
formed in succession, from the very first, to its state of full perfection,
we should probably be able to compare it with some one of the in-
complete animals themselves, of every order of animals in the
creation, being at no stage different from some of those inferior
orders ; or, in other words, if we were to take a series of animals
from the more imperfect to the perfect, we should probably find an
imperfect animal corresponding with some stage of the most per-
fect."!

With the great accession of facts with which Comparative Anatomy
has since been enriched, particularly from monographs detailing dis-
sections of the Invertebrate animals, we may now attempt a more exact
enunciation of the resemblance which a higher organised animal pre-
sents to those of a lower order in its progress to maturity : and the
consequent extent to which the law of ' Unity of Organisation ' may
be justly, and without perversion of terms, be predicated of animal
structures. We shall see some grounds for the statement that the

* Lecture XVITL Insecta, p. 235.

•}• Hunterian MS. quoted in Physiological Catalogue, vol. i. p. 4.

368 LECTUKE XXIY.

more perfect animal is at no stage of its development different troni
some of the inferior species ; but we shall obtain proof that such cor-
respondence does not extend to every order of animals in the creation.

The extent to which the resemblance, expressed by the term ' Unity
of Organisation,' may be traced between the higher and lower organised
animals, bears an inverse ratio to their approximation to maturity.

All animals resemble each other at the earliest period of their
development, which commences with the manifestation of the as-
similative and fissiparous properties of the polygastric animalcule :
the potential germ of the Mammal can be compared, in form and
vital actions with the Monad alone, and, at this period, unity of
organisation may be predicated of the two extremes of the Animal
Kingdom. The germ of the Polype pushes the resemblance farther,
and acquires the locomotive organs of the Monad, — the superficial
vibratile cilia, — before it takes on its special radiated type. The
Acalephe passes through both the Infusorial and Polype stages, and
propagates by gemmation, as well as spontaneous fission, before it
acquires its mature form and sexual organs. The fulness of the
unity of organisation which prevails through the Polypes and larval
Acalephes, is diminished as the latter acquire maturity and assume
their special form.

The Ascidian MoUusks typify more feebly and transiently the polype
state in passing from that of the cercarii-forni ciliated larva to the
special molluscous form. The Gasteropods and Bivalves obey the lav/
of unity of organisation in the spontaneous fissions of their amorphous
germ, and in its ciliated epithelium, by which it gyrates in the ovum ;
but they proceed at once to assume the molluscous type without
assuming that of the Polype ; the Bivalve retaining the acephalous
condition, the Univalve ascending in its development to the acqui-
sition of its appropriate head, jaws, and organs of sense.

Thus all mollusks are at one period like Monads, at another Acepha-
lans ; but scarcely any typify the Polypes, and none the Acalephes. In
the Encephalous division we meet with many interesting examples of
the prevalence of unity of organisation at early periods, which is lost in
the diversity of the special forms as development proceeds. Thus the
embryos of the various orders of Gasteropods are nudibranchiate ; but
only a few retain that condition of the respiratory system through
life. The naked Gasteropods are at first univalve Mollusks, like the
great bulk of the class at all periods. The testaceous Cephalopods
first construct an unilocular shell, which is the common persistent
form in Gasteropods, and afterwards superadd the characteristic
chambers and siphon. This simple fact would of itself have disproved
the theory of evolution, if other observations of the phenomena of

CEPHALOPODA. 369

development had not long since rendered that once favourite doctrine
untenable.

Thus as we trace the development of the Molluscous animal, we
find the application of the term unity of organisation progressively-
narrowed as development advances : for whilst all MoUusca manifest,
at their earliest and most transitory period, a resemblance to the
lowest or monadiform zoophytes, only the lowest order of Mollusca in
the next stage of development represents the polypes ; and all analogy
to the radiated type is afterwards lost, until we reach the summit of
the Molluscous series, when we find it illusively, though interestingly,
sketched by the crown of locomotive and prehensile organs upon the
head of the Cephalopods.

In the great Articulated branch of the animal kingdom^ there is
unity of organisation with the Molluscous series at the earliest periods
of development, in so far as the germ divides and subdivides and
multiplies itself; but the correspondence does not extend to the
acquisition of the locomotive power by superficial vibratile cilia :
the progeny of the fissiparous primitive nucleated cell begin at
once to arrange themselves into the form of the Vibrio or apodal
worm, while'' those of the Molluscous germ diverge into the polype-
form or into a more special type.

Unity of organisation prevails through a very great proportion of
the Articulate series in reference to their primitive condition as apodal
worms. Only in the Arachnida apparently, the nucleated cells
are aggregated under a form more nearly like that of the mature
animal, before they are metamorphosed into its several tissues. In lower
or more vermiform Condylopods, the rudimental conditions of the lo-
comotive appendages, which are retained in the Anellides and the lower
Crustaceans, are passed through in the progress of the development of
the complex-jointed limbs. In the great series of air-breathing insects,
we have seen that the diverging branch of Myriapoda manifests at
an early period the prevailing hexapod type, and that all Insects are
at first apterous, and acquire the jointed legs before the wings are fully
developed. An articulate animal never passes through the form of
the Polype, the Acalephe, the Echinoderm, or the Mollusk : it is
obedient to the law of unity of organisation only in its monad stage :
on quitting this, it manifests the next widest relations of uniformity as
a Vibrio or apodal worm ; after which the exact expression of the law
must be progressively contracted in its application as the various
Articulata progressively diverge to their special types in the acquisition
of their mature forms.

In the proper Radiated series itself we discern the same principle :
the radiated type culminates in the Echinoderms ; but the most typical

370 LECTURE XXIV.

forms, called emphatically star-fishes, are pedunculated in the embryo-
state, at least in one family, and so far manifest conformity of or-
ganisation with the Polypes and the vast and almost extinct tribes of
the Pentacrinites, before acquiring their free and locomotive maturity.

It will be found when we enter upon the consideration of the
development of the Vertebrate embryo, that its unity of organisation
with the Invertebrata is restricted to as narrow and transitory a point
as that of the Articulate with the Molluscous series. Manifesting the
same monad-like properties of the germ, the fissiparous products
proceed to arrange and metamorphose themselves into a vermiform
apodal organism, distinguished from the corresponding stage of the
Insect by the Vertebrate characteristics of the nervous centres, — viz.
the spinal chord and its dorsal position ; whereby it is more justly
comparable to the apodal fish than to the worm.

Thus every animal in the course of its development typifies or
represents some of the permanent forms of animals inferior to itself;
but it does not represent all the inferior forms, nor acquire the
organization of any of the forms which it transitorily represents.
Had the animal kingdom formed, as was once supposed, a single
and continuous chain of being progressively ascending from the
Monad to the Man, unity of organisation might then have been
demonstrated to the extent in which the theory has been maintained
by the disciples of the Geoffroyan school.

There is only one animal form which is either permanently or tran-
sitorily represented throughout the animal kingdom : it is that of
the infusorial Monad, with the consideration of which the present
survey of the Invertebrate animals was commenced, and which is to
be regarded as the fundamental or primary form.

Other forms are represented less exclusively in the development of
the animal kingdom, and may be regarded as secondary forms.
These are, the Polype, the Worm, the Tunicary, and the Lamprey ;
they are secondary in relation to the animal kingdom at large,
but are primary in respect of the primary divisions or sub -kingdoms.

Thus the Radiata, after having passed through the monad-stage
enter that of the polype ; many there find their final development ;
others proceed to be metamorphosed into the Acalephe or the
Echinoderm.

All the Articulata, at an early stage of their development, assume
the form or condition of the apodal and acephalous worm ; some find
their mature development at that stage, as the parasitic Entozoa ;
others proceed to acquire annulations, a head, rudimental feet,
jointed feet, and finally wings : radiating in various directions
and degrees from the primary or fundamental form of their sub-
kingdom.

CEPHALOPODA. 371

The MoUusca pass from the condition of the ciliated Monad to that
of the shell-less Acephalan, and in like manner either remain to work
out the perfections of that stage, or diverge to achieve the develop-
ment of shells, of a head, of a ventral foot, or of cephalic arms, with
all the complexities of organisation which have been demonstrated in
the^^^concluding Lectures of this Course.

The Vertebrated ovum having manifested its monadiform relations
by the spontaneous fission, growth, and multiplication of the primordial
nucleated cells, next assumes, by their metamorphosis and primary ar-
rangement, the form and condition of the finless cartilaginous fish,
from which fundamental form development radiates in as many and
diversified directions and extents, and attains more extraordinary
heights of complication and perfection than any of the lower secondary
types appear to be susceptible of. The ultimate stages of these de-
velopments, the various permanent or mature structures of the Verte-
brated series, with their physiological and other relations, will form
the subjects of succeeding lectures.

For the kind and patient attention with which the present course
has been honoured, I must again, Mr. President and Gentlemen,
express my most sincere thanks, and, with every good wish, respect-
fully bid you Farewell !

To Mr. Cooper's notes of the Lectures, as orally delivered, I have
added the details contained in my written notes, which, for want of
time, were omitted, or only briefly alluded to in the theatre. R. O.

B B 2

GLOSSAEY

OF ANATOMICAL AND OTHER SCIENTIFIC TEKMS USED IN THESE
LECTURES.

Abdomen. (Lat. abdo, I conceal.) The posterior and principal cavity containing

the bowels and many other viscera of the animal. The abdomen is distinct from

the thorax in crustaceans, spiders, and insects.
Abdominales. (Lat. abdomen.^ An order of fishes, so called from the attachment

of the ventral fins to the abdomen behind the pectorals.
Aberrant. (Lat. aberro, I wander from.) This term is applied to those species

which deviate most from the type of their natural group.
Abranchiate. (Gr. a, without; hragchia, gills.) When an animal is devoid of

gills.
AcALEPHA. (Gr. akalephe, a nettle.) The class of radiated animals with soft

skins, which have the property of stinging like a nettle.
AcANTHOCEPHALA. ( Gr. alicmtkos, a spine; kephale, a head.) The order of intes-
tinal worms having the head armed with spines or hooks.
AcARus. (Gr. akari, a mite.) The name of a genus of Arachnida, to which the

cheese-mite and allied spacies belong.
AcARiDiE. The family of which the genus Acarus is the type,

AcASTA. (Gr. akaste.) A name arbitrarily applied to a genus of Barnacles, para-
sitic upon sponges.
Acephalous. (Gr. a, without; kephale, head.) Headless. The animals in which

a distinct head is never developed.
AcEPHALocYST. The parasitic hydatid, which consists of a cyst or bag without a

head.
AcETABULA. (Lat. acetabulum, a shallow cup.) The fleshy sucking-cups with

which many of the invertebrate animals are provided.
Acini. (Lat. acinum, a berry.) The secerning parts of glands, when they are

suspended like grains or small berries to a slender stem.
Acoustic. (Gr. akouo, I hear.) Appertaining to sound, or the organ of hearing.
AcRiTA. (Gr. akritos, confused.) A term applied to the lowest animals, in which

the organs, and especially the nervous system, were supposed to be confusedly

blended with the other tissues.
Actinia. (Gr. akti7i, a ray.) The genus of Polypes, which have many arms

radiating from around the mouth.
AcTiNocEROs. (Gr. aktin, a ray; keras, a horn.) A generic term, signifying the

radiated disposition of the horns or feelers.
Adipose. (Lat. adeps, fat.) Fatty.
Akera. (Gr, a, without ; ker as, a horn.) The family of Mollusca, without horns

or feelers.
Alar, (Lat. ala, a wing.) Belonging to a wing.

Albuminous. (Lat. albumen, white of egg. ) Consisting of albumen, or the sub-
stance which forms the white of an egg.
Aliform. Shaped like a wing.
Alula. A little wing.
Ambulacra. (Lat. ambulacrum, an avenue or place for walking.) The perforated

series of plates in the shell of the sea-star or sea-urchin.
Ambulatory. (Lat. ambtdo, I walk.) An animal or a limb made for walking.
Ammonites. An extinct genus of Mollusca, allied to the Nautilus, which inhabited

a chambered shell, called Ammonite from its resemblance to the horns on the statues

of Jupiter Amnion.
Amorphous. (Gr. a, without; morpJte, form.) Bodies devoid of regular form.
Amphipods. (Gr. ainphi, on both sides; pous, a foot.) The order of Crustacea,

which have feet for both walking and swimming.

B B 3

374 GLOSSARY.

Amphistoma. (Gr. arnphi ; stoma, a mouth.) The genus of suctorial parasitic

worms, which have pores like mouths at both ends of the body.
Ampulla. (Lat. a bottle.) A membranous bag, shaped like a leathern bottle.
Anaima. (Gr. a, without; aima, blood.) The name given by Aristotle to the

animals which have no red blood, and which he supposed to be without blood.
Analogue. A part or organ in one animal which has the same function as another

part or organ in a different animal. See Homologue.
Anastomose. ( Gr. ana, through ; stoma, mouth. ) When the mouths of two

vessels come into contact and blend together, or when two vessels unite as if such

kind of union had taken place.
Androgynous. ( Gr. aner, a man ; gune, a woman. ) The combination of male

and female parts in the same individual,
Anellata. (Lat. annellus, a little ring.) The worms in which the body seems to

be composed of a succession of little rings, characterised by their red blood.
Anellide. The anglicised singular of Aiiellata.
Anenterous. (Gr. a, without; enteron, a bowel.) The animalcules of infusions

which have no intestinal canal.
Annulated. (Lat. annulus, a ring.) When an animal or part appears to be com-
posed of a succession of rings.
Anourous. (Gr. a, without ; aura, a tail.) Tail-less.
Antenna. (From the Latin for yard-arm.) Applied to the jointed feelers or

horns upon the heads of insects and Crustacea, and sometimes to the analogous

parts, which are not jointed in worms and other animals.
Anthozoa. (Gr. anthos, a flower; zoon, an animal.) The class of Polypes,

including the actinia and allied species, commonly called animal-flowers.
Antiperistaltic. ( Gr. anti, against ; and peristaltic. ) When the vermicular con-
tractions of a muscular tube follow each other in a direction the reverse of the

ordinary one.
Antlia. ( From the Latin for pump. ) Restrictively applied to the spiral instrument

of the mouth of butterflies and allied insects, by which they pump up the juices

of plants.
Aorta. (Gr. aorte, the wind-pipe; and also the name of the great vessel springing

from the heart, which is the trunk of the systemic arteries. ) It is exclusively applied

in the latter sense in modern anatomy,
Aphidian. Belonging to the insect called aphis, or plant-louse.
Apical. (Lat. apex, the top of a cone.) Belonging to the pointed end of a cone-
shaped body.
Apodal. (Gr. a, without; poda, feet.) Footless; without feet or locomotive

organs : fishes are so called which have no ventral fins.
Apterous. (Gr. a, without; pteron, a \vmg.) Wingless species of Insects or Birds.
Arachnida. (Gr. arachne, a spider.) Spiders, and the animals allied to them in

structure.
Arborescent. (Lat. arbor, a tree.) Branched like a tree.
Arthrodial. (Gr. arthron, a joint.) It is restricted to that form of joint in

which a ball is received into a shallow cup.
Articulata. (Lat. articulus, a joint. ) Animals with external jointed skeletons or

jointed limbs.
AsciDiAN. (Gr. as^os, a bottle, ) The shell- less acephalous MoUusks, which are

shaped like a leathern bottle.
Automatic, (Gr. automates, self-moving.) A movement in a living body without

the intervention or excitement of the will.
Axilla (from the Latin for armpit) ; and applied to other parts of the animal body

which form a similar angle.
AzYGOS. (Gr. a, without; zugos, yoke.) Single, without fellow.

Baculite. Ah extinct genus of molluscous animals allied to the Nautilus, which
inhabited a straight-chambered shell, resembling a staff; whence the name of the
genus, from haculus, a staff.

Balanoids. (Gr. halanos, an acorn.) A family of sessile Cirripeds, the shells of
which are commonly called acorn-shells.

Basilar. (Lat. basis, a base.) Belonging to the base of the skull.

GLOSSARY. 375

Batrachia. ( Gr. hatrachos, a frog. ) The order of reptiles including the frog.
Belemnite. (Gr. helemnon, a dart.) An extinct genus of molluscous animals

allied to the sepia, and provided with a long, straight, chambered, conical shell in

the interior of the body.
Bifid. Cleft into two parts, or forked.
Bifurcate. Divided into two prongs or forks.
Bilateral. Having two symmetrical sides.
BiLOBED. Divided into two lobes.
Bipartite. Divided into two parts.
Bituberculate. With two knobs or tubercles.
Bivalve. When a shell consists of two parts, closing like a double door. The

Mollusca, so protected, are commonly called bivalves.
Bothriocephalus. ( Gr. bothros, a pit ; kephale, a head. ) The genus of tape- worms

with depressions on the head.
BoTRYLLi. (^Gx.hotrus, a bunch of grapes.) A little cluster of berry-shaped

bodies.
Brachial. (Gr. hrachion, the arm.) Belonging to the arm.
Brachiopoda. (Gr. brachion ; poda, feet.) A class of acephalous Mollusca, with

two long spiral fleshy arms continued from the side of the mouth.
Brachyura. (Gr. brachuSj short; oura, tail.) The tribe of Crustacea with short

tails, as the crabs.
Brachyurocjs. Short tailed ; usually restricted to the Crustacea.
Branchia. (Gr. bragchia, the gills of a fish.) The respiratory organs which

extract the oxygen from air contained in water.
Branchiopods. (Gr. bragchia, gills ; poda, feet.) Crustacea in which the feet sup-
port the gills.
Bryozoa. (Gr. bruon, moss ; zoon, animal.) A class of highly-organised Polypes,

most of the species of which incrust other animals or bodies like moss.
Buccal. (Lat. fewcm, mouth or cheeks.) Belonging to the mouth.
Byssus (from the Greek word, signifying the silky filaments which project from

the bivalve called Pinna). Applied to the analogous parts in other Mollusks.

C.SCUM and Cjfxa. (Lat. ccecus, blind.) A blind tube, or productions of a tube

which terminate in closed ends.
Canthus. ( Gr. kanthos.) The corner of the eye.
Capitate. ("Lat. caput, head.) When a part is terminated by a knob like the

head of a pin.
Carapace. The upper shell of the crab or tortoise.
Cardia. (Gr. kardia, the heart or stomach.) The opening which admits the

food into the stomach ; also the region called the pit of the stomach.
Carnivorous. (Lat. caro, flesh ; voro, I devour.) The animals which feed on flesh.
Caruncle. (Lat. caruncula.') A soft wart-like eminence.
Caudal. (Lat. cauda, a tail. ) Belonging to the tail.
Cauda Equina. The brush of nerves which terminates the spinal marrow in the

human subject, and the analogous part in the lower animals.
Cellular TISSUE. (Lat. ceZ/a, a cell.) The elastic connecting tissue of the dif-
ferent parts of the body, which every where forms cells or interspaces containing

fluid.
Centipede. (Lat. centum, a hundred ; pes^ a foot.) A genus of insects with very

numerous feet.
Cephalo-thorax. (Gr. kephale, head; thorax, chest.) The anterior division of

the body in spiders, scorpions, &c., which consists of the head and chest blended

together.
Cephalic. ( Gr. kephale, head. ) Belonging to the head.
Cephalopoda. (Gr. kephale; poda, feet.) The class of molluscous animals in

which long prehensile processes or feet project from the head.
Cercari^. (Gr. kerkos, a tail.) The animalcules whose body is terminated by a

tail-like appendage.
Cercariiform. Shaped like Cercariae.
Cercte. (Gr. kerkos, a tail.) The feelers which project from the hind part of the

body in some insects.

B B 4

376 GLOSSARY.

Cerealia. ( Ceres, the Goddess of corn.) The name of the natural family of plants
which produce corn, oats, rye, &c.

Cestoidea. ( Gr. kestos, a girdle. ) The order of intestinal worms with long and
flat bodies like tape, usually called tape-worms.

Chelonia. (Gr. chelone, a turtle.) The order of reptiles including the tortoises
and turtles.

Chele. ( Gr. chele, a claw. ) Applied to the bifid claws of the Crustacea, scor-
pions, &c.

Chelicera. (Gr. chele, a claw ; keras, a horn.) The prehensile claws of the
scorpion, which are the homologues of Antennae.

Chilognatha. (Gy. cheilos, a lip; c/nathos, a jaw.) The order of many-footed
insects typified by the Gaily -worm or lulus.

Chilopoda. (Gr. cheilos, a lip; poda, feet.) An order of many-footed insects
typified by the Centipede.

Chitine. (Gr. chiton, a coat.) The peculiar chemical principle which hardens the
integument of insects.

Choledochus. (Gr, chole, bile; ddche, receptacle.) The tube formed by the
union of the hepatic and cystic ducts.

Chorion. From the Greek word signifying the membrane which encloses the
foetus, and applied generally to the outer covering of the ovum.

Chrysalids. (Gr. cArwsos, gold.) The stage of the butterfly immediately pre-
ceding its period of flight, when it is passive, and enclosed in a case which some-
times glitters like gold.

Chyle. (Gr. chulos, juice.) The nutrient fluid extracted from the digested food
by the action of the bile.

Chyme. (Gr. chumos, juice.) The digested food which passes from the stomach
into the intestines.

Cicatrix. From the Latin, signifying scar.

Cilia. (Lat. cilium, an eyelash.) The microscopic hair-like bodies which cause,
by their vibratile action, currents in the contiguous fluid, or a motion of the Iwdy
to which they are attached.

Ciliated. Provided with vibratile cilia.

Ciliobrachiata. The class of Polypes in which the arms are provided with vibra-
tile cilia.

Ciliogrades. (Lat. cilium; and gradior, T walk.) The order of Acalephce which
swim by the action of cilia.

Circumgyrations. (Lat. circum, around; gyrus, a circle.) Motions in a circle.

Cirri. (Lat. cirrus, a curl.) The curled filamentary appendages, as the feet of the
barnacles.

CiRRiGERous. Supporting cirri.

CiRRiGRADEs. Moviug by cirri.

CiRRiPEDS or CiRRiPEDiA. (Lat. cimis, a curl ; pes, a foot.) A class of articulate
animals having curled jointed feet. Sometimes written Cirrhipedia and Cirrho-
poda.

Clavate. (Lat. clavus, a club.) Club-shaped; linear at the base, but growing
gradually thicker towards the end.

Cloaca. (Lat. c/oaca, a sink.) The cavity common to the termination of the
intestinal, urinary, and generative tubes.

Clyfeiform. (Lat. clypeus, a shield; forma, shape.) Shield-shaped ; applied to
the large prothorax in beetles.

Coarctate. (Lat. coarcto, I compress.) The pupa of an insect, which is enve-
loped by a case, which gives no indication of the parts it covers.

Ccelelmintha. (Gr. Ao/Zos, hollow ; hehnins, an intestinal worm.) The intestinal
worms which are hollow, and contain an alimentary tube in the cavity of the body.

Coleoptera. (Gr. koleos, a sheath; pteron, a wing.) The order of insects in
which the first pair of wings serves as a sheath to defend the second pair.

Columella. (From the Latin for a small column.) Used in Conchology to signify
the central pillar around which the spiral shell is wound.

Com:\ussi)ral. (Lat. committo, I solder.) Belonging to a line or part by which
other parts are connected together.

GLOSSARY. 377

CoNCHJFERs. (Lat. cc»?icAa, a shell ; /ero, I bear.) Shell-fish; usually restricted

to those with bivalve shells.
CoNDYLOPODS. ( Gr. kondvdos, a joint ; pons, a foot.) The articulate animals with

jointed legs, as insects, crabs, and spiders.
Coriaceous. (Lat. corium, hide.) When a part has the texture of tough skin.
CoRNUA. (Lat. cornu, a horn.) Horns or horn-like processes.
Cornea. (Lat. corneus, horny.) The transparent horny membrane in front of

the eve.
Corneous. Horny.
CoRNEULE. Diminutive of cornea ; applied to the minute transparent segments

which defend the compound eyes of insects.
Cretaceous. (Lat, creta, chalk.) Belonging to chalk.
Crinoid. (Gr. krinon, a. \i\y ; eidos,]ike.) Belonging to the Echinoderma which

resemble lilies ; the fossils called stone-lilies or encrinites are examples.
Crura. (Lat. crus, a leg. ) The legs of an animal, or processes resembling legs.
Crustacea. (Lat. crwsfa, a crust.) The class of articulate animals with a hard

skin or crust, which they cast periodically.
Cryptobranchiate. (Gr. kruptos, hidden; bragcliia, g\\\s.) Those molluscous and

articulate animals, which have no conspicuous gills.
Cryptogamic. (Gr. kruptos, concealed; gamos, marriage.) The animals or

plants in which the organs of generation are concealed.
Cyclobranchiata. (Gr. kuklns, round ; hragchia, gills.) The molluscous animals

which have the gills disposed in a circle.

Dec APOD A. (Gr. deca, ten; pons, afoot.) The crustaceous and molluscous ani-
mals which have ten feet.
Decollated. (Lat. decollo, to behead.) The univalve shells in which the apex or

head is worn off in the progress of growth.
Deciduous. Parts which are shed, or do not last the lifetime of the animal.
Dehiscence. (Lat. dehisco, to gape.) The splitting open of the bag containing

the eggs.
Deflected. Bent down,
Dejiodex. ( Gr. demos, lard ; dex, a boring worm. ) The worm-like parasite of

the human sebaceous follicles.
Dendritic. (Gr. dendron, a tree.) Branched like a tree.
Dermal. (Gr. derma, skin.) Belonging to the skin.
Dibranchiata. ( Gr. dis, twice ; hragchia, gills. ) The order of Cephalopods

having two gills.
Diccelous. (Gr. dis ; koilos, a cavity.) A heart with two cavities.
Didactyle. (Gr. dis ; and dacttdos, a finger.) A limb terminated by two fingers.
Digitate. (Lat. digitus, a finger.) When a part supports processes like fingers.
Dimidiate. (Lat. dimidium, hsdi.) Divided into two halves.
Dioecious. (Gr. dis, twice, and oikos, a house,) The species which consist of male

and female individuals.
DiMYARY. (Gr. dis ; wmow, a muscle.) A bivalve whose shell is closed by two

muscles,
DiPTERA. (Gr. dis ; pteron, a wing.) The insects which have two wings.
Discoid, (hat. discus, a quoit.) Quoit-shaped.

DisTOMA. (Gr. dis ; stoma, mouth.) The intestinal worms with two pores.
Diverticulum. (From the Latin for a bye-road.) Applied to a blind tube

branching out from the course of a longer one.
Dorsad. (Lat. dorsum, the back.) Towards the back.
Dorsibranchiate. (Lat. dorsum; and branchia, gills.) The Mollusca with gills

attached to the back.
DoKSO-iNTESTiNAL. A part which is on the dorsal aspect of the intestine.
Ductus. A duct or tube which conveys away the secretion of a gland.
Duodenum. The first portion of the small intestine, which, in the human subject,

equals the breadth of twelve fingers.

Ecdvsis. (From the Greek, signifying the act of stripping.) Moulting of the
skin.

378 GLOSSARY.

EcHiNODEK-MS. ( Gr. echinos, a hedgehog ; derma, skin. ) The class of radiated

animals, most of which have spiny skins.
Edentulous. From the Latin word for toothless.
Edriophthalma, ( Gr. edraios, sitting or sessile ; and ophthalmos, an eye. ) The

Crustacea with sessile eyes.
Elytra. (Gr. elutroji, a sheath.) The wing sheaths formed by the modified an-

terior pair of wings of beetles.
Emarginate. (Lat. emargino, to remove an edge.) When an edge or margin

has, as it were, a part bitten out.
Emunctories. (Lat. emungo, to wipe the nose.) Parts which carry out of the

body useless or noxious particles.
Enaliosaur. (Gr. ewaZ/os, marine; sawros, a lizard.) An extinct order of marine

gigantic reptiles allied to crocodiles and fishes.
Encephala. (Gr. en, in; kephale, head.) The molluscous animals which have a

distinct head.
Entomology. ( Gr. entoma, insects ; logos, a discourse. ) The department of Na-
tural History which treats of insects.
Entohostraca. (Gr. entoma, insects; osfracon, a shell.) The order of small

Crustaceans, many of which are enclosed in an integument, like a bivalve shell.
Entozoa. (Gr. entos, within; zoon, animal.) The animals which exist within

other animals.
Eocene. (Gr. eos, the dawn; kainos, recent.) The tertiary period, in which the

extremely small proportion of living species indicates the first commencement or

dawn of the existing state of animate creation.
Epidermal. (Gr. epidermis, the cuticle.) Belonging to the cuticle or scarf-skin.
Epimeral. ( Gr. epi, upon ; meron, a limb. ) The part of the segment of an ar-
ticulate animal which is above the joint of the limb.
Epiploon. ( From the Greek. ) It is the fatty membrane which covers or occupies

the interspaces of the entrails in the abdomen.
Episternal. (Gr. e/)i, upon ; sferwora, the breast-bone.) The piece of the segment

of an articulate animal which is immediately above the middle inferior piece or

sternum.
Epithelium. The thin membrane which covers the mucous membranes : it is

analogous to the epiderm of the skin.
Epizoa. ( Gr. epi, upon ; zoo7i, animal. ) The class of low organised parasitic

Crustaceans which live upon other animals.
Errantes. (Lat. erro, I wander.) An order of the class Annelida, remarkable

for their locomotive powers.
ExciTO-MOTORY. The function of the nervous system by which an impression is

transmitted to a centre, and reflected so as to produce contraction of a muscle

without sensation or volition.
ExosMOSE. (Gr. ex, out of; otheo, I expel.) The act in which a denser fluid is

expelled from a membranous sac by the entry of a lighter fluid from without.
ExuviuM. (From the Latin, signifying the skin of a serpent.) The skin which is

shed in moulting.
ExuviAL. Any part which is moulted.

Facet. (From the French.) A flat surface, with a definite boundary.

Fascicle. (From the l^aiin fasciculus.) A small bundle.

Filiform. (Lat. filum, a thread ; forma, a shape. ) Thread-shaped.

FissiPAROUS. (Lat. Jindo, I cleave; pario, I produce.) The multiplication of a
species by the voluntary cleavage of the individual into two parts.

Flabelliform. ( Lat. ^rt6eZZ?<?n, a fan. ) Fan-shaped.

Flagellum. (From the Latin.) An appendage to the legs of the Crustacea re-
sembling a whip.

Flexors, (l^at. flecto, I bend.) The muscles employed in bending a limb.

Flexuous. a bending course.

Foliaceous. (Lat. folium, a leaf.) Shaped or arranged like leaves.

Follicle. (Lat. follicutus, a small bag.) Minute secreting bags which commonly
open upon mucous membranes.

FossiLiFERous. (Lat. fossilis, any thing dug out of the earth ; and ferro, I bear.)

GLOSSARY. 379

Applied to the strata which contain the remains of animals and plants, to which

remains' Geologists now restrict the term Fossil.
FucivoRous. (Lat. fucus, sea- weed ; and voroy I devour.) Animals which subsist

on sea-weed.
FusiFORjvL (Lat. /itSMS, a spindle; and /orraa, a shape.) Spindle-shaped.

Ganglion. ( Gr. gagglion, a knot. ) A mass of nervous matter, forming a centre

from which nervous fibres radiate.
Gasteropoda. (Gr. gaster, stomach ; pous, a foot.) That class of molluscous

animals which have the locomotive organ attached to the under part of the body.
Gemmifarous. (Lat. gemma, a bud ; pario, I bring forth.) Propagation by the

growth of the young, like a bud from the parent.
Gemmule. (Dim. oi gemma.) The embryos of the radiated animals at that stage

when they resemble ciliated monads.
Globose. (Lat. globus, a globe.) Globe-shaped.
Glossology. (Gr. glosse, the tongue j Gr. logos, discourse.) The science of

scientific language.
Granules. ( Dim. of ^rrawwrn, a grain. ) Little grains.
Gynglymoid. (Gr, gigglumos, a hinge.) A joint formed for motion on one plane.

Haustellate. (Lat. haurio, I drink.) The structure of mouth adapted for
drinking or pumping up liquids ; also the insects which possess that kind of
mouth.
Heljiinthoid. (Gr, helmins, an intestinal worm.) Worm-shaped.
Hemelytra. (Gr. hemisu, half; elytron, a sheath.) A wing, of which one half is

opaque and firm like an elytrum.
Hemiptera. (Gr. hemisu, half; pteron, a wing.) The order of insects in which

the anterior wings are hemilytra.
Hepatic. (Lat. hepar, liwer.) Belonging to the liver.
Herbivorous. (Lat. herha, grass; voro, I devour.) The animals which subsist on

grass.
Hermaphrodite, {Hermes, Mercury; Aphrodita, Venus.) An individual in which

male and female characteristics are combined.
Heterogangliate. (Gr. Ae^eros, diverse ; gagglion.) The animals with the gan-
glionic nervous system, and the ganglions scattered often unsymmetrically.]
Heteromorphous. (Gr. heteros, another; morphe, form.) Of an irregular or

unusual form, applied to the larvae of certain insects which differ in form from

the imago, and applicable to the true larval state of all insects.
Hexapod. (Gr. hexa, six ; pous, a foot.) The animals with six legs, such as true

insects.
Histological. ( Gr. histos, a tissue ; logos, discourse. ) The doctrine of the tissues

which enter into the formation of an animal and its diflferent organs.
HoMOGANGLiATE. ( Gr. Jiomos, like; ganglion.) The animals with the ganglionic

nervous system and symmetrical arrangement of the ganglions.
HoMOLOGUE. (Gr. homos ; logos, speech.) The same organ in different animals

under every variety of form and function.
HoMOMORPHOus. ( Gr, Aowos, like ; morphe, form.) Of similar form.
HoMOPTERA. ( Gr. homos, like ; pteron, a wing. ) The insects in which the four

wings have a similar structure, but restricted in its application, to a section of

Hemiptera.
Hyaline. (Gr. hualos, crystal.) The pellucid substance which determines the

spontaneous fission of cells.
Hydatid. (Gr. hudatis, a vesicle.) A bladder of albuminous membrane, con-
taining serous fluid ; generally detached ; sometimes with an organised head

and neck.
Hydra. (Gr. hudra, a water-serpent.) The modern generic name of freshwater

Polypes.
Hydriforsi. Similarly-formed Polypes.
Hydrozoa. (Gr. hudra; zoow, animal.) The class of Polypi organised like the

Hydra.
HviiENOPTERA. ( Gr. humen, a membrane ; pteron, a wing.) The order of insects

including the bee, wasp, &c. which have four membranous wings.

380 GLOSSARY.

Imbricated. (Lat. i/nbricatus, tiled.) Scales which lie one upon another like
tiles.

Ingluvies. a crop or partial dilatation of the oesophagus.

Inopercular. Univalve shells which have no operculum or lid.

Instrumenta Cibaria. (Lat. cibus, food.) The parts of the mouth in insects con-
cerned in the acquisition and preparation of the food.

Interambulacra. The imperforate plates which occupy the intervals of the per-
forated ones, or ambulacra, in the shells of the Echinoderms. See Ambulacra.

Interganglionic. (Lat. JH^er, between ; and ga7iglion.) The nervous chords in the
intervals of the ganglions, which they connect together.

Interstitial. (Lat. interstitium.) Relating to the intervals between parts.

Intr-auterine. (L.at. intra, within; uterus, the womb.) The development of the
embryo which takes place within the womb.

Intussusception. CLat. uitus, within; suscipio, I take up.) When part of a
tube is inverted within a contiguous part.

Invertebrata. (Lat. in, used in composition to signify 7iot, like un ; vertebra, a bone
of the back. ) Animals without back-bones.

IsocYCLUs. ( Gr. W05, equal ; kuMos, a rmg.) An animal composed of a succession
of equal rings.

IsoPODA. (Gr. isos, equal ; pous, a foot.) An order of Crustaceans in which the
feet are alike, and equal.

Labium. Latin for a lip ; but applied only to the lower lip in Entomology.
Labrum. Latin for a lip ; but applied only to the upper lip in Entomology.
Lamellibranchiata. {\uat. lamella, a plate ; bragchia, g\\\?,.) The class of ace-
phalous Mollusks with gills in the form of membranous plates.
Lamelliform. Shaped like a thin leaf or plate.
Laniariform. (Lat. lanio, to cut or tear; forma, shape.) Shaped like the

canine teeth of the Carnivora, which are called laniaries from their office.
Larva. (Lat. larva, a mask. ) Applied to an insect in its first active state,

which is generally different from, and as it were masks the ultimate form. Larvi-

form, shaped like a larva.
Larviparous. (Lat. larva; pario, I produce.) The insects which produce their

young in the condition of larva;.
Lemniscus. (The Latin for riband. ) Applied to the minute riband-shaped appendages

of the generative pores in Entozoa.
Lepidoptera. (Gr. lepis, a scale; pteron, a wing.) The order of insects in which

the wings are clothed with fine scales, as butterflies and moths,

Macroura. (Gr. makros, long ; oura, tail.) The tribe of decapod Crustacea which
have long tails, as the lobster.

Malacology. {Gy. makikos, soft; logos, discourse.) The history of the soft-
bodied or molluscous animals, which were termed Malakia by Aristotle.

Malacostraca. (Gt. ynalakos ; ostrakon, a shell.) The name given by Aristotle
to the modern Crustacea, because their shells were softer than those of the Mol-
lusca, or ordinary shell-fish.

Mammalia. (L.at. matiwia, a breast.) The class of animals which give suck to
their young.

Mandibulata, CLat, mandibula, a jaw.) The insects which have mouths pro-
vided with jaws for mastication ; the term mandible is restricted in Entomology
to the upper and outer pair of jaws.

Mantle. The external soft contractile skin of the Mollusca, which covers the
viscera and a great part of the body like a cloak.

Marsupial. (Lat. marsupium, a purse.) The tegumentary pouch, in which the
embryo is received after birth, and protected during the completion of its de-
velopment.

Mastodon. (Gr. mastos, a teat; odon, a tooth.) A genus of extinct quadrupeds
allied to the elephant, but having the grinders covered with conical protuberances
like teats.

Maxilla. (From the Latin for a jaw.) In Entomology restricted to the inferior
pair of jaws.

GLOSSARY. 381

Median. Having reference to the middle line of the body.

Medulla oblongata. The oblong medullary column at the base of the brain, from
which the spinal chord or marrow is continued.

Medus.i;. a genus or family of soft radiated animals or acalephes, so called because
their organs of motion and prehension are spread out like the snaky hair of the
fabulous Medusa.

Mesentery. (Gr. rnesos, intermediate ; and enterosy entrail.) The membrane
which forms the medium of connection between the small intestines and the
abdomen.

Mesogastric. {Gv.mesos; and ^as/er, stomach.) The membrane which forms the
medium of attachment of the stomach to the walls of the abdomen.

Mesonotum. {Gy. mesos, middle; notos, back.) The middle piece of that half of
the segment which covers the back.

Mesosternum. ( Gr. mesos ; sternon, the breast.) The middle part of that half of
the segment which covers the bi'east.

Mesothorax. {Gr. mesos, middle; and thorax, the chest.) The intermediate of
the three segments which form the thorax in insects.

Metathorax. {Gv.meta, after; thorax.) The hindmost of the three segments
which compose the thorax of an insect.

Miocene. (Gr. vhcw??, less ; /?amos, recent.) The tertiary epoch in which a mi-
nority of fossil shells are of the recent species.

Molecules. (Dim. of moZe^, a mass.) Microscopic particles.

Mollusca. (Lat. mollis, soft.) The primary division of the Animal Kingdom,
characterised at page 13.

Monad. (Gr. mn7ias, unity.) The genus of the most minute and simple micro-
scopic animalcules, and shaped like spherical cells. Monadiform, like a monad.

Monoculus. (Gr. monos, single; Lat. ocuhts, an eye.) The animals which have
but one eye.

Monomvary. (Gr. monos, single; inuon, a muscle.) A bivalve whose shell is
closed by one adductor muscle.

Monothalamous. {Gr. monos ; thalamos, a chamber.) A shell forming a single
chamber, like that of the whelk.

Morphological. ( Gr. morphe, form ; logos, a discourse. ) The history of the mo-
difications of form which the same organ undergoes in different animals.

Motory. The nerves which control motion.

Multivalve. (Lat. multus, many; valvce, folding-doors.) Shells composed of
many pieces or valves.

IMyelexcephala. {Gr. muelos, marrow; egkephalon, brain.) The primary divi-
sion of animals characterised by a brain and spinal marrow.

IVIyriapoda. { Gr. murios, ten thousand; pous, foot.) The order of insects cha-
racterised by their numerous feet.

Nacreous. Pearly, like mother-of-pearl.

Natatory. An animal or part formed for swimming.

Nematoidea. (Gr. nema, a thread ; eidos, like.) The intestinal worms, which are

long, slender and cylindrical like threads.
Nematoneura. (Gr. 7iema, a thread ; neuron, a nerve.) The animals in which

the nervous system is filamentary, as in the star-fish.
Nervures. (Lat. nervus, a sinew.) The delicate frame- work of the membranous

wings of insects.
Neurilemjia. ( Gr. neuron, anerve ; lemma, a covering. ) The membrane which sur-
rounds the nervous fibre.
Neurology (Gr. neuron a nerve ; logos, a discourse.) The science of the nervous

system.
Neuroptera. {Gr. neuron, a nerve; pteron, a wing.) The order of insects with

four wings, characterised by their numerous nervures, like those of the dragon-fly.
Nidamental. (Lat. nidus, a nest.) Relating to the protection of the egg and

young, especially applied to the organs that secrete the material of which many

animals construct their nests.
Nodule. (Dim of nodus, a knot.) A little knot-like eminence.
Normal. (Lat. norma, rule.) According to rule, ordinary or natural.

382 GLOSSARY.

NoTAL. (Gr. notos, the buck.) Belonging to the back.

Nucleated. Having a nucleus or central particle; applied to the elementary
cells of animal tissues, the most important properties of which reside in the nu-
cleus.

NuDiBRACHiATE. ( Lat. nMc?Ms, naked ; brachia, axms.) The Polypes, whose arms
are not clothed with vibratile cilia,

NuDiBRANCHiATE. (Lat. nudus, naked ; bragchia, giWs.) An order of Gasteropods
in which the gills are exposed.

OcTOPODA. (Gr. octo, eight ; pous, a foot.) Animals with eight feet. The name
of the tribe of Cephalopods with eight prehensile organs attached to the head.

CEsoPHAGus. The gullet or tube leading from the mouth to the stomach.

Olfactory. (Lat. olf actus, the sense of smelling.) Relating to that sense.

Onychoteuthis. ( Gr. onux, a hook ; teuthis, a calamary.) The genus of Cala-
maries armed with hooks or claws.

Oolite. (Gr. oon, egg; lit hos, stone.) An extensive group of secondary lime-
stones composed of rounded particles, like the roe or eggs of a fish.

Operculum. (From the Latin for lid.) Applied to the horny or shelly plate
which closes certain univalve shells ; also to the covering of the gills in fish, and
to the lids of certain eggs.

Oral. (Lat. os, the mouth.) Belonging to the mouth or to speech.

Orthocera and Orthoceratite. ( Gr. or^/jos, straight ; Aeras, horn.) The extinct
Cephalopods which inhabited long conical chambered shells like a straight horn.

Orthoptera. ( Gr. or^Aos, straight ; pteron, a -wmg.) The order of insects, with
elytra and longitudinally folded wings.

Osseous. (Lat. os, a bone. ) Bony.

Otolithes. (Gr. oms, an ear ; lithos, a. stone.) The stony or chalky bodies belong-
ing to the internal ear.

Ovariuih. (Lat. ovum, an egg.) The organ in which the eggs or their elementary
and essential parts are formed.

OviGEROUs. (Lat. ovum, an egg ; gero, I bear.) Parts containing or supporting
eggs.

Oviparous. (Lat. ovum ; pario, I bring forth. ) The animals which bring forth eggs.

Ovipositor, {l^at. ovum ; pono, I place.) The organ in insects, which is often
large and complicated, for the transmission of the eggs, during exclusion, to
their appropriate place.

Ovoviviparous. (Lat. ovwn, egg; vivus, alive; pario, I produce.) The animals
which produce living young, hatched in the egg within the body of the parent,
without any connection with the womb.

Pal.«ontology. ( Gr. /)aZaios, ancient ; owta, beings; fc^ros, discourse. ) The his-
tory of ancient extinct organised beings.

Pallial. (Lat. pallium, a cloak.) Relating to the mantle or cloak of the Mol-
lusca.

Palliobranchiata. (Lat. pallium; branchia, gills.) The class of acephalous
Mollusca in which the gills are developed from the mantle.

Palpi. (Lat. palpo, 1 touch.) The organs of touch developed from the labium
and maxillae of insects.

Papilla. (Lat. for nipple.) Minute soft prominences, generally adapted for
delicate sensation.

Papyraceous. (Gy. papuros, paper.) Of the consistency of paper.

Parenchyma. The soft tissue of organs ; generally applied to that of glands.

Parietes. (Lat. paries, a wall.) The walls of the different cavities of an animal
body.

Pectinated. (Lat. pecten, a comb.) Toothed like a comb.

Pectinibranchiata. (Lat. /)ec^e?i, a comb ; branchia, gills.) The order of Gas-
teropods in which the gills are shaped like a comb.

Pediform. (Lat. pes, a foot.) Shaped like a foot.

Peduncle. From the Latin pedunculus, a stalk.

Pedunculated. Suspended or supported by a stalk.

Pelagic. (Gr. pelagos, sea.) Belonging to the deep sea.

GLOSSARY. 383

Pentacrinite. (Gr. penta^ five ; krinos, hair.) A pedunculated star-fish with five

rays : they are, for the most part, fiassil.
Pergameneous, (luat. pergamen, parchment.) Of the texture of parchment.
Periostracum. (Gr. peri, around ; ostrakon, shell.) The membrane analogous to

scarf-skin, which covers shell.
Peristaltic. (Gr. peri ; stello, to range.) The vermicular contractions and motions

of muscular canals, as the alimentary, the circulating, and generative tubes.
Peritoneal. ( Gr. peritonaios, the covering of the abdomen. ) Restricted to the
lining membrane of that cavity.

Peritrema. (Gr. peri, around; trema, hole.) The raised margin which sur-
rounds the breathing holes of scorpions.

Petiolate. (Lat. petiolus, a fruit stalk. ) Ducts supported or suspended by a
slender stalk.

Pharynx. The dilated beginning of the gullet.

Pharyngeal. Belonging to the pharynx.

Phragmocone. ( Gr. j9^ra^ma, a partition ; ^owos, a cone.) The chambered cone
of the shell of the Belemnite.

Phytophagous. ( Gr. phuton, a plant ; phago, I eat. ) Plant-eating animals.

Pigmental. (Lat. pigmentum, paint.) The cells which secrete the coloured par-
ticles of the skin and eye, and the membrane formed by such cells.

Pinnate. (Lat. pinna, a feather or fin.) Shaped like a feather, or provided with
fins.

Plasma. The fluid part of the blood, in which the red corpuscles float : also
called liquor sanguinis.

Plastron. The under part of the shell of the crab and tortoise.

Plexus. ( Gr. pleko, I twine.) A bundle of nerves or vessels interwoven or
twined together.

Pleiocene. (Gr. pleion, more; kainos, recent.) The tertiary strata, which are
more recent than the miocene, and in which the major part of the fossil testacea
belong to recent species.

Pleistocene. (Gr. pleistos, most; kaitios, recent.) The newest of the tertiary
strata, which contains the largest proportion of living species of shells.

Plic^. (Lat. plica, a fold.) Folds of membrane.

Plumose. (Lat. pluma, a feather.) Feathery, or like a plume of feathers.

Pneumatic. ( Gr. pneuma, breath.) Belonging to the air and air-breathing organs.

Podophthalma. (Gr. pons, a foot; ophtJialmos, an eye.) The tribe of Crustacea
in which the eyes are supported upon stalks.

Polygastria. (Gr. polus, many ; gaster, a stomach.) The class of infusorial ani-
malcules which have many assimilative sacs or stomachs.

Polypi. (Gr. polus ; pons, a foot.) The class of radiated animals with many pre-
hensile organs radiating from around the mouth.

Prolegs. The wart-like tubercles which represent legs on the hinder segment of
caterpillars.

Prothorax. (Gr.pro, before, and thorax.) The first of the three segments which
constitute the thorax in insects.

Psychical. ( Gr. psuche, the soul. ) Relating to the phenomena of the soul, and
to analogous phenomena in the lower animals,

Pteropoda. ( Gr. pteron, a wing ; pons, a foot. ) The class of Mollusca in which
the organs of motion are shaped like wings.

PuLMOGRADE. {luaX. pulmo, a lung; gradior, I walk.) The tribe of MeduScP,
which swim by contractions of the respiratory disc.

PuLMONATA. (Lat. pulmo.) The order of Gasteropods that breathe by lungs.

Pupa. ( From the Latin for a doll or little image. ) The passive state of an insect
immediately preceding the last.

PupiPARous. (hat. pupa; pario, I produce. ) The insects that bring forth their
young in the pupa state.

Pylorus. From the Greek. The aperture which leads from the stomach to the in-
testine.

Pyriform. (Lat. pijrum, a pear.) Pear-shaped.

Quadrifid. Cleft in four parts.

384 GLOSSARY.

Radiata. (liat. rctflinft, a ray.) The name of tlie lowest primary division of the

animal kingdom.
Ramose. (Lat. 7'nr??ms, a branch.) Branched.
Renifoum. (Lat. ren, a kidney.) Kidney-shaped.
Reptilia. (Lat. repto, I creep.) The class of Vertebrate animals with imperfect

respiration and cold blood.
Rete Mucosum. The cellular layer between the scarf-skin and true skin, which is

the seat of the peculiar colour of the skin.
Rhyncholithes. (Gr. rhunchos, a beak ; lithos,a stone.) Beak-shaped fossils ; the

extremities of the mandibles of Cephalopods, allied to the Nautilus.
Rotifera. (Lat. rota, a wheel; fero, I bear.) The name of the class of infusorial

animalcules, characterised by the vibratile and apparently rotating ciliary organs

upon the head.

Sat.pians. (Gr. 5'aZpe, a kind of fish. ) The order of tunicated Mollusca which

float in the open sea.
Sarcofhaga. (Gr. sarx, flesh; phago, I eat.) Flesh-eating animals.
Sacciform. Shaped like a sac or bag.
ScuTiBRAXCHiATA. (Lat. scutum, a shield; branchia, gills.) The order of gas-

teropodous Mollusca, in which the gills are protected by a shield-shaped shell.
Sebaceous. (Lat. se&M??j, tallow. ) Like lard or tallow.
Segmentation. The act of dividing into segments.
Semilunar. Crescent-shaped, like a half-moon.
Sepal. The divisions of the calyx of a flower.
Septa. Partitions.
Sericteria. (Gr. serikos, silky.) The glands which secrete the silk in the '^ilk-

worm.
Serrated. (Lat. serra, a saw.) Toothed like a saw.
Sessile. Attached by a base.

Set^. (From the Latin for a bristle.) Bristles, or similar parts.
Setigerous. Bristly.
Siliceous. (Lat. silex, flint.) Flinty.
Sinus. A dilated vein or receptacle of blood.
SiPHONOsTOMOus. ( Gr. siphoii, a tube ; stoma, a mouth.) Animals furnished with

a suctorious mouth like a tube. The term is usually applied to Crustacea so

characterised.
Spatulate. {l^at. spatula.) Shaped like a spatula.
Spermatheca. (Gr. sperma, seed; theke, sheath.) A receptacle attached to the

oviducts of insects.
Spermatophora. (Gr. sperma ; phero, I bear.) The cylindrical capsules or sheaths

in the Cephalopods which convey the sperm. They are also called the moving

filaments of Needham, their discoverer.
Spermatozoa. (Gr. sperma j zoon, an animal. ) The peculiar microscopic moving

filament and essential parts of the fertilising fluid.
Sphincter. (Gr, sphigkter.) The circular muscles which contractor close natural

apeirtures.
Spicula. (Lat. spiculum, a point or dart.) Fine pointed bodies like needles.
Spinnaret. The articulated tubes with which spiders fabricate their webs.
Spiracles. (Lat. spiro, I breathe.) The breathing pores in insects.
Squamous. (Lat. *<7Mawia, a scale. ) Arranged like scales.
Stemmata. (Lat. stemma. ) The simple and minute eyes of worms, and those which

are added to the large compound eyes.
Sterelmintha. (Gr. stereos, solid; helmins, an intestinal worm.) Intestinal

worms which have no true abdominal cavity, and which were called " parenchyma-
tous" by Cuvier, as the tape-worms.
Sternal. The aspect of the body where the sternum or breast bone is situated.
Stigmata. (Gr. stigma, a mark.) The breathing pores of insects.
Stomato-gastric. (Gr. stoina, a mouth; gaster, a stomach.) The system of

nerves which are principally distributed upon the stomach and intestinal canal.
Strepsiptera. (Gr. strepho, I twist; pteron, a wing.) The singular order of in-

GLOSSARY. 385

•sects discovered by Mr. Kirby, in which the first pair of wings is represented by

twisted rudiments.
SuBMuscuLAR. Beneath muscles or muscular layer.
SuBCEsoPHAGEAL. Beneath the gullet.
SucTORiA, CLaL sugo, I suck.) The animals provided with mouths for sucking,

and the appendages of other parts organised for sucking or adhesion.
SuPRA-CEsoPHAGEAL. Above the gullet.
SuTURAL. Appertaining to a suture.
Suture. (Lat. suo, I sew.) The immoveable junction of two parts by their

margins.

T^NioiD. (Gr. tainia, a riband; eidos, like.) Riband-shaped, like the Taenia or

tape-worm.
Tapetum. (Lat. iapetum, a carpet.) The coloured layer of the choroid coat of the

eye.
Tarsus. (Gr. tarsos, a part of the foot.) Applied to the last segments of the

legs of insects.
Tectibranchiate. (Lat. tego, I cover; hranckia, gills.) The order of Moll u sea in

which the gills are covered by the mantle.
Tergal. (Lat. <er^Mm, the back.) Belonging to the back.
Tetrabranchiate. ( Gr. tetra, four ; hragchia, gills. ) The order of Cephalopods

with four gills,
Teuthid^. (Gr. few^Ais, a calamary.) The family of Cephalopods, of which th©

calamary is the type.
Thoracic. Belonging to the thorax.
Thysanoura. ( Gr. thusanoi, fringes ; oiira, a tail. ) A family of apterous insects

with fringed tails.
Tracheae. (Gr. tracheia, the rough artery or windpipe.) The breathing tubes of

insects.
Trachklipods. ( Gr. trachelos, the neck ; pous, a foot. ) The Mollusca which have

the locomotive disc or foot attached to the head.
Trematoda. (Gr. trema, a pore. ) The order of Entozoa characterised by suc-
torial pores.
Trenchant. Sharp-edged, cutting.
Tridactyle. Three-fingered.
Trilobate. Divided into three lobes.
Trilobite. An extinct genus of Crustacea, the upper surface of whose body is

divided into three lobes.
Triradiate. Consisting of three spokes or rays.
Trophi. ( Gr. trophos, a nourisher. ) In insects, the parts of the mouth employed

in acquiring and preparing the food.
Tuberculate. Warty, or covered with small rounded knobs.
Tunicata. (Lat. tunica, a cloak.) The class of acephalous Mollusca which are

enveloped in an elastic tunic not defended by a shell.

Uncinated. Beset with bent spines like hooks.

Univalve. (Lat. urnis, one; valvce, doors.) A shell composed of one calcareous
piece.

Vasiform. (Lat. vas, a vessel.) Shaped like a bloodvessel or tube.

Ventral. Relating to the inferior surface of the body.

Ventricular. (Lat. ventriculus, a ventricle or small cavity, like those of the

heart or brain.) Belonging to a ventricle.
Vermes, (Lat. vermis, a worm.) Worm-like animals : applied in a very extensive

sense by Linuceus.
Vertebrata. (Lat. vertebra, a bone of the back; from vertere, to turn.) The

highest division of the Animal Kingdom, characterised by having a back bone.
Verticillate (Lat. verticillus, a whirl.) Arranged like the rays of a wheel or

spindle.
Vermiform. Worm-shaped.

VisicuL.*. ( Lat. t'esica, a bladder. ) Receptacles like little bladders.

C C

386 GLOSSARY.

Villi. Small processes like the pile of velvet.
Vitelline. ( hat. vitellus, yolk.) Of or belonging to the yolk.
Viviparous. (Lat, vivus, alive; pario, I bring forth.) The animals which bring
forth their young alive.

XiPHOsuRA. (Gr. xiphos, a sword; oura, a tail.) A family of Crustacea with
sword-shaped tails, as the Limulus.

Zoophyte. (Gr. zoon, animal; phyton, plant.) The lowest primary division of
the Animal Kingdom, which includes many animals that are fixed to the ground,
and have the form of plants.

INDEX.

Acanthocephala, 60, 61.
Acarus foUiculorum, 252.
Acephalocyst, 44, 46.
Acephalous Mollusca, 268.
Acetabula of Cephalopods, 345.
Acrita, 15.
Actinia, 87.

Actheres, 151, 152, 154.
Actinocyclus, 18.
Alcyonium, 88.
Alimentary Canal of

Anellata, 133, 135.

Arachnida, 257.

Berije, 106.

Brachiopoda, 278.

Bryozoa, 98.

Cephalopoda, 323.

Cirripedia, 158.

Crustacea, 177.

Diplostomum, 59.

Distoma, 56, 58.

Echinoderma, 121, 125.

Epizoa, 152.

Gastropoda, 299.

Insecta, 216.

Lamellibranchiata, 282.

Pteropoda, 292.

Tunicata, 271.
Ammonites, 331.
Anaima, 11.
Androgynous organs of

Anellata, 144.

Bothriocephalus, 52.

Cirripedia, 158.

Distoma, 57.

Gasteropoda, 307.

Pteropoda, 293.

Tsen'iae, 49.
Anellata, 129. Orders of, 132.
Anellides, 11, 14.
Animals, classes of, 15.
Animal Kingdom, tabular view of, 16.
Animal matter preserved from loss by

Polygastria, 28.
Anodon, marsupial gills of, 288. Ova

of, 289.
Antennas of

Anellides, 131.

Crustacea, 166.

Insects, 194.

c c

Anthozoa, 89.

Aphides, larval generation of, 233. As-
tonishing fecundity of virgin females,
235. Ordinary generation of, 235.

Aphrodita, 130, 135.

Aplysia, 299, 300, 305, 311, 312.

Arachnida, 250. Comparison with in-
sects, 250.

Arenicola, 139.

Argonauta, 107, 344, 348.

Arms of Cephalopods, 344.

Articulata, 13.

Ascaris lumbricoides, 66.
vermicularis, 67.

Ascidians, 13, 270. Compound, 272.

Astacus fluviatilis, 169, 187, 188.
marinus, 170, 179.

Asterias, 14, 113.

Atoll, 89.

Avicula margaritifera, 287.

Baculite, 331.

Balanoids, 155.

Barnacle, 157.

Barrier reef, 89.

Barry, Dr. Martin, 24. 78.

Bee, development of, 240.

Belemnite, 333. Its mantle, 337. Fins,

338. Arms, 338. Ink-bag, 335.
Belcher, Capt. Sir E., R.N., 324.
Bergmehl, 40.

Blood, 130. Corpuscules, 78.
Bonnet, 143. 268.
Bothriocephalus latus, 50. 52. Punc-

tatus, 53, 54. Development of, 53.
Brachiopoda, 277.
Branchiopods, 181.
Broderip, W. J. Esq., 171.
Buckland, Dr., 175. 329.
Buffon, 28.

Bulla, its gastric shells, 300.
Burmeister, Prof, 248.
Bryozoa, 93.

Carinaria, 293.

Carpenter, Dr., 286.

Cell, organic, 25. Nucleated, 24, 25.

Centipede, 192. 201. 216. 225.

Cephalopoda, 13. 302.

Cestoidea, 48, 54.

2

388

INDEX.

Chambered cells, formation of, 329.

Chlamydomonas, 24.

Chrysalis, 246.

Cilia, vibratile, 17. 19. 34. 97. 278. 289.
310. 312.

Ciliobrachiata, 93.

Cirrigrades, 107.

Cirripedia, 155.

Cirroteuthis, 341.

Classes of animals, 15.

Clio, 292, 293.

Clitellum, 145.

Coarctate metamorphosis, 238.
Cocoon, 145. 246.

Coelelmintha, male generative organs, 71.
73. Female generative organs, 73. 75.
Comatula, 114. 128.
Compound polypes, 85. 88. 95. As-

cidians, 271.
Coralline of Ellis, 86.
Coral Islands, 89.
Corallium rubrum, 87, 88.
Crab, 172.
Crustacea, 162.
Cuvier, 1. 11, 12. 130.
Cyanjea, 105.
Cymothoa, 164.
Cysticercus, 47.

Dalyell, Sir J. G., 111.
Decapod dibranchiates, 340.
Demodex folliculorum, 251.
Development of

Acalephas, 109.

Anellata, 146.

Arachnida, 265.

Bothriocephala, 53.

Bryozoa, 100.

Cephalopoda, 360.

Cirripedia, 160.

Crustacea, 185. 191.

Epizoa, 153.

Gasteropoda, 311.

Insecta, 229. 249.

Lamellibranchiata, 289.

Tunicata, 273. 276.
Dibranchiate Cephalopods, 339.
Dictyocha, 18.

Digestion in Polygastria, 20.
Dimyaries, 281.
Diplozoon paradoxum, 59.
Distoma hepaticum, 56.
clavatum, 56.
lanceolatum, 58.
Dragon-fly, 197.
Duval, M., on Belemnites, 336.

Earthworm, 134. 137. 145.
Ecdysis, (See Moulting.)
Echinococcus, 46, 47.
Echinorhyncus, 61.

Edwards, Dr. Milne, 272.
Ehrenberg, 19, 37, 38. 106. 117.
Ellis, 86.
Elytra, 195.
Enaima, 11.
Encrinites, 114.
Encephalous Mollusca, 268.
Entomostraca, 164.

Entozoa, 42. Orders of, 44. Tenacity
of life, 79. Human, 42. 44. 47, 48, 49.
56. 58. 62.
Entrochi, 114.
Eocene, 41. 512.
Epizoa, 147.

Equivocal generation, 54. 79.
Eschricht, Prof., 50. 293. 345.
Extinct chambered shells, 313.
Eye in Acalephae, 106.

Anellata, 141.

Arachnida, 256.

Ciripedia, 161.

Crustacea, 174.

Entozoa, 56. 68.

Epizoa, 154.

Gasteropoda, 306.

Insecta, 212.

Lamellibranchiata, 285.

Nautilus, 321.

Polygastria, 20.

Rotifera, 35.

Sepia, 352.

Trematoda, 60.

Farre, Dr. A., 93.

Feet, tubular, of Echinoderms, 115.

119. 125.
Filaria bronchialis, 64. Medinensis, 63.

Oculi, 64.
Fission, spontaneous, 23, 26, 27, 85. 111.
Flustra, 99.
Fringing reefs, 91.

Ganglions function in Articulata, 171.

Garner, Mr., 285.

Gasteropoda, 293. Orders of, 294.

Gemmation, 23.

Generative organs in

Anellata, 144.

Arachnida, 263.

Cephalopoda, 326. 358.

Cirripedia, 158.

Crustacea, 184.

Echinoderma, 117. 124. 128.

Epizoa, 153.

Gasteropoda, 307.

Insecta, 225.

Lamellibranchiata, 287.

Pteropoda, 293.

Tunicata, 272.
Generation, equivocal, 32. 79. Fissi-
parous, 23. 26, 27. 85. HI. Larvi-

INDEX.

389

parous, 230. Genamiparous, 23.

85. 92. 111. 275. Oviparous, 230.

Pupiparous, 230. Rapid rate of, in

Infusoria, 26.
Germinal vesicle, 37.
Goadby, Mr., 285.
Gonium, 23.
Grant, Prof., 106. 306.

Haliotes, 301, 363.
Hamite, 332.
Hearing, organ of, in

Cephalopoda, 322, 352.

Crustacea, 173.

Gasteropoda, 306.

Insecta, 21 1.

Laraeliibranchiata, 287.
Heart, 6.

In Anellida, 138.

Arachnida, 258.

Brachiopoda, 278.

Cephalopoda, 324, 325. 355.

Crustacea, 179.

Fish, 7.

Gasteropoda, 301.

Insecta, 221.

Lamellibranchiata, 283.

Pteropoda, 292.

Snail, 7.

Tunicata, 271.
Hermaphrodite, 184, 229.
Herold, 223. 242. 265.
Heterogangliata, 13. 268.
Hobbes, Thomas, 29.
Holothuriadae, 11, 113, 125.
Homogangliata, 13. 130.
Humble-bee, economy of, 241.
Hunter, John, 3, 12, 103. 170. His ex-
periment on a fly, 219. On the circu-
lation in Insects, 222.
Hunterian Lectures defined, 3.
Hyalea, 292.

Hydatina, generation of, 37,
Hydra, 82.
Hydrozoa, 82.

Ichneumon, parasitic habits of, 244.
Insect metamorphosis, 236. Analogy of

development of human embryo with,

248. Of Marsupialia with, 249. Of

Batrachia with, 249.
Insecta, 192. Orders of, 195. Wings

of, 195.
Infusoria, 17. Tenacity of life in, 38.

Siliceous deposits of, 40.
Instrumenta Cibaria, 214.
Invertebrata, 12.
Isopoda, 168.
lulus, 199.

Jones, Prof. R., 225.

Kolliker, Dr., 231. 232.

Lamarck, 12.

Larva, definition of, 236.

Leech, 133, 136,141.144. Teeth of,

133.
Leeuwenhoek, 39. 287. 289.
Lepas, 156, 161.
Lepadoids, 155.
Lernaea, 148.
Leucophrys, 17.
Limn£Bus, 307.
Limulus, 164,
Linguatula, 71.
Linnaeus, 9, 10.
Lister, Joseph, 86.
Lithedaphus, 291.
Liver, in

Anellata, 134, 135.

Arachnida, 258.

Brachiopoda, 278.

Cephalopoda, 323.

Cirripedia, 158.

Echinoderma, 115.

Entozoa, 71.

Gasteropoda, 297, 308.

Insecta, 220.

Lamellibranchiata, 280.

Pteropoda, 292.

Tunicata, 271.
Locomotion of Infusoria, 19.
Rotifera, 35.
Locusta, 193.
Lobster, 170. 179.
Loricate Infusoria, 18. 34.
Loven, Dr., 146.
Lyell, Chas. Esq., 41. 312.

Malacostraca, 164.

Mantel], Gideon, D.C.L., &c., 5.

Marsupial sacs, 108, 109. 185. 288.

Medusa;, 102. 109.

Melanine, 355.

Metamorphosis of

Acalephae, 109. 112.

Anellida, 146.

Ascidians, 273.

Cirripedia, 160. 162.

Comatula, 128.

Crustaceans, 186, 190.

Entozoa, 80.

Epizoa, 153, 154.

Gasteropoda, 309.

Insecta, 230. 249.

Lamellibranchiata, 289.

Polypes, 86. 100.
Millepora, 89.
Mites, 254.
Mollusca, 13. 268.
Monad, 18, 20. 25.

390

INDEX.

Monomyaries, 281.
Moulting of

Arachnida, 267.

Cirripedia, 161.

Crustacea, 167.

Epizoa, 154.

Insecta, 245.
Mussel, 284.
Myelencephala, 12.
My gale, 255.
Mytilus, 284.

Nacre, 286.

Nais, 144."

Napula, 23.

Navicula, 18.

Nautilus Pompilius, 315.

Needham, moving filaments, 358.

Nematoidea, 62.

Nematoneura, 15.

Nervous system,

Acaleph«, 106.

Anellata, 141.

Arachnida, 254.

Brachiopoda, 278.

Cephalopods, 320. 348, 351.

Cirripedia, 157.

Crustacea, 13. 164. 169. 172.

Echinoderma, 14. 116. 124. 127.

Entozoa, 56. 68.

Epizoa, 152.

Gasteropoda, 302, 306.

Insecta, 199. 210.

Lamellibranchiata, 284.

Nautilus, 320.

Pteropoda, 243.

Tunicata, 271.

Vertebrata, 12.

Metamorphoses of, in insects, 209.
Nidamental capsules, 309.

glands, 308, 327.
Non-g^.nglionic chords, their function in

Articulata, 171.
Notoramata, 34.
Nucleated cells, 24, 25. 364.

Obtected metamorphosis, 238.
Octopod dibranchiates, 340.
Oestrus Horainis, 238.
Oken, Prof, 198. 364.
Operculum, 60. 296.
Ophiura, 115.
Organic matter, 28.
Orthoceratite, 331.
Ova of Acalephse, 109.

Anellata, 145.

Arachnida, 264.

Bothriocephala, 53.

Cephalopoda, 360.

Cirripedia, 159.

Crustacea, 185.
Epizoa, 152.
Gasteropoda, 311.
Insecta, 331.
Lamellibranchiata, 289.
Polygastria, 26.
Polypi, 85, 87, 100.
Rotifera, 37.
Tunicata, 273.
Oviparous generation, its final purpose
in Infusoria, 31.

Pagurus, nerves of, 170.

Paludina vivipara, 299.

Pearl, 287.

Pedicellarics, 120.

Penella, 151.

Peniculus, 149.

Pentacrinus, 114. 129.

Per-centage of Fossil shells in tertiary
strata, 312.

Phillips, Prof., 336.

Phragmocone, 333.

Physalia, 107.

Planaria, 60.

Poison-glands, 216. 229. 260.

Polygastria, 16. Generation of, 22.
Mouths of, 20. Ovarium of, 26. Shells
of, 18. Sleep, none in, 20. Stomach
in, 20. Teeth of, 20. Testes of,
26. Vascular system, 22.

Polierschiefer, 40.

Polypi, 81.

Portuguese man-of-war, 107.

Pteropoda, 291.

Pupa, definition of, 236.

Radiaria, 111.

Radiata, 14.

Rathke, Dr., 187. 290.

Reaumur, 167.

Reparative power, 84. 143.

Reproduction of parts, 143. 183. 207.

287.
Respiratory organs in

Acalephaj, 104.

Anellata, 137.

Arachnida, 259.

Brachiopoda, 278.

Cephalopoda, 325. 357.

Cirripedia, 158.

Crustacea, 181.

Echinoderma, 122.

Gasteropoda, 294. 301.

Insecta, 223.

Lamellibranchiata, 283.

Tunicata, 272.
Rhizostoma, 103.
Rotifer, 36.
Rotifera, 33. Alimentary canal in,

INDEX.

391

36. Cilia of, 34. Locomotion in, 35.

Muscular system, 34, Nervous system

in, 35. Shells of, 34. Teeth of, 35.

Testis, 37. Vascular system, 36.

Vesicul^ seminales, 37. Wheels of,

34.
Rotation of embryo in ovo, 289. 311.
Rudistes, 291.
Rudolphi, 42, 53.

Salivary glands in

Cephalopods, 323.

Cirripeds, 158.

Echinoderms, 122.

Entozoa, 70.

Gasteropods, 298.

Insects, 220.

Pteropods, 292.
Salpa, 276.
Sarcoptes Galei, 252.
Sars, M., 111.
Savigny, 275.
Scaphite, 332.
Schultze, Prof. His experiment on

spontaneous generation, 32.
Scorpion, 260. 264.
Sea-anemone, 87.
Sea-grapes, 360.
Sepia, 349.
Sertularia, 86.
Sharpey, Prof, 116.
Shell of Brachiopoda, 277.

Cephalopoda, 328. 341.

Gasteropoda, 295.

Lamellibranchiata, 286.

Pteropoda, 291.

Absorption of, 296.
Ship-borer, 287.
Siebold, Prof, 76. 109. 285.
Siliceous deposits of Infusoria, 40. 43.
Sinistral shells, 295.
Siphoniferous shell, formation of, 329.

Its function, 330.
Sipunculus, 128.
Skeleton, external, in

Arachnida, 251.

Crustacea, 163.

Echinoderma, 114. 117.

Insecta, 193.
Slug, 10.
Soemmering, 54.
Spallanzani, 39.
Spermatophora, 358.
Spermatozoa of

Acalephae, 108.

Anellida, 146.

Cephalopoda, 358.

Echinoderma, 135.

Lamellibranchiata, 288.

Nematoidea, 73.

Polypes, 99.

Sphinx Ligustri, 242.

Spiders, loves of, 262. Webs of, 262.

Spines of Echinus, 117.

Spiroptera Hominis, 65.

Spirula, 314. 341,

Spontaneous fission, 23. 111. 144.

Squilla, 169.

Star-fish, 113.

Stomapoda, 177.

Stone-lilies, 114.

Stokes, C. Esq., 331. 341.

Strongylus Gygas, 65.

Stutchbury, Sam., Esq., 91.

Sub-kingdoms of Animals, 12.

Svrammerdam, 245.

Swan, Jos. Esq., 170.

Tape-worms, geographical distribution

of, 48. 50. 54.
Taenia Solium, 48.
Teeth of

Echinus, 121.

Leech, 133.

Nereids 135.
Tenacity of life in

Entozoa, 79.

Infusoria, 39.
Tentacula of

Hydra, 83.

Nautilus, 31'"'. 319.
Terebratula, 277.
Teredo, 287.
Tetrabranchiata, 31
Thompson, Mr. J. V., 129. 160.
Tiedemann, Prof, 116.
Tongue of

Cephalopods, 353.

Limpet, 298.

Nautilus, 323.

Whelk, 298.
Torpidity, 39.
Touch, organs of,

Arachnida, 257.

Cephalopods, 322. 351.

Crustacea, 173.

Gasteropods, 306.

Insecta, 210.
Tracheliastes, 151.
Transition from Radiata to Mollusca,

269.
Trematoda, 55. 60.
Trichina spiralis, 62.
Trichocephalus dispar, 65.
Trilobite, 165.
Trophi, 215.
Tunicata, 267.
Turrilite, 332.

Urinary organs, 22L 258. 284. 302.
325.

392

INDEX.

Valenciennes, M., 321.
Valentin, Prof., 120. 123.
Vascular system of

Anellides, 136. 139.

Asterias, 1 16.

Echinus, 123.

Holothuria, 126.

Insecta, 321.

Medusa, 104.

Nautilus, 324.

Sepia, 367.
Venous cavity of Cephalopods,
follicles of ditto, 325.

324,

Vermes, 10.
Vertebrata, 12.
Vesiculje seminales, 26.
Vibrio Tritici, 79.
Volvox, 20, 23.
Von Buch, Prof,, 336.
Vorticella, 21.

Wagner, Prof., 105.
Wasp, economy of, 240.

Xiphosura, 164.

THE END.

ERRATA.

Page 15. line 10. from bottom, for " several," read " earlier."

15. line 9. from bottom, for " one," read " ones,"

148. line 8., for " 87," read « 78."

156. line 13., for " fine," read « five."

192. line 7. from bottom, for " insects." read " insects,".

215. line 16. from bottom, for " canine," read " incisive."

215. line 5. from bottom, for " appendage," read " process."

227. line 16,, for " Teh," read " The."

243. line 22., for « ength," read " length."

249. line 10. from bottom, for " do," read " does."

267. line 6. from bottom, for " Cirripeda," read " Cirripedia.

272, line 4. from bottom, for " 115," read " 116."

289. line 11., for " litoralis," read " littoralis."

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