enclosed in canal by a strong band, the anterior annular | the sacro-iliac ligaments require to be of great strength,
ligament, and their surfaces are invested by a synovial because the sacrum, and with it the entire trunk, are sus
membrane, which facilitates their movements to and fro pended by them on the two innominate bones.
beneath that ligament; as they pass downwards in front of The Hip Joint is a ball-and-socket joint; the ball is the Hip joint.
the fingers they are enclosed in a strong fibrous sheath head of the femur, and the socket the cup-shaped acetabu-
lined by a synovial membrane, and the tendon of the super-lum in the haunch bone, the depth of the cup being in
ficial flexor is pierced by the deep flexor, so that the latter creased by a ligament which is attached around the brim.
may reach the third phalanx into which it is inserted. A large capsular ligament, which is especially strong in
Four rounded muscles, the lumbricales, arise in the palm front, encloses the articular surfaces. The ligament is
from the deep flexor tendons, turn round the radial borders lined by a synovial membrane, which also invests the neck
of the first phalanges, and are inserted one into the extensor of the thigh bone. Within the joint is the round or sus-
tendon on the dorsum of each finger; these muscles bend pensory ligament attached to the head of the thigh bone
the first phalanges on the metacarpal bones, but from their and to the sides of the depression at the bottom of the
insertion into the extensor tendons they also extend the acetabulum. Whilst the hip joint possesses considerable
second and third phalanges on the first; as they are much mobility, it has much more stability than the shoulder,
used in playing stringed instruments, they have been called owing to the acetabulum being deeper than the glenoid
"fiddlers'muscles.” The fingers are extended or straightened fossa, and the greater strength and tension of the fibres of
by muscles inserted into the back of the second and third its capsular ligament. The muscles which move the thigh
phalanges; the extensor muscles descend from the back of at the hip joint are situated either behind the joint, where
the fore-arm,-one, the common extensor, subdivides into they form the fleshy mass of the buttock, or at the front
four tendons, one for each finger, but in addition the index and the inner side of the thigh. They are inserted either
and little have each a separate extensor muscle, the tendon into the femur or fascia lata, and the great and small
of which joins that of the common extensor. The index trochanters serve as their principal surfaces of attachment.
finger possesses more independent movement than the The thigh can be bent on the abdomen by the action of
other digits—hence its more frequent use as a “ pointer;" the psoas, iliacus, and pectineus, which lie in front of the
the extensor tendons of the little and ring fingers are joint; it can be extended or drawn into line with the
usually united together, so that these digits are associated trunk by the glutæus-maximus and medius; it can be
in their movements. Abduction and adduction of the abducted or drawn away from the opposite thigh by the
fingers are caused by seven small muscles situated in the glutæus maximus, medius, and minimus, which muscles
intervals between the metacarpal bones,-hence called are of large size, and form the fleshy mass of the buttocks.
interossei; four of these lie on the back of the hand, three It can be adducted or drawn to touch its fellow, or, if
on its palmar surface; they are inserted into the sides of slightly bent, drawn in front of its fellow, by the adductor
the first phalanges, and either pull the fingers away from a longus, brevis, and magnus, which muscles are inserted
line drawn through the middle finger or approximate them into the linea aspera, and form the fleshy mass on the
to that line. Too great abduction is checked by the trans- inner side of the thigh; and by the pectineus and quad-
verse metacarpal ligament. The human hand is a perfect in ratus femoris. It can be rotated outwards by the obturator
strument of prehension; not only can the individual fingers and gemelli muscles, the glutæus maximus, pyriformis, and
be bent into hooks, but the thumb can be thrown across the quadratus femoris; and rotated inwards by the glutæus
front of the palm, so that it can be opposed to the several medius, minimus, and tensor fasciæ femoris.

In standing
fingers, and objects can therefore be grasped between it and erect the hip joints are fully extended, and the mechanical
them; but further, this power of opposing the thumb permits arrangements in and around these articulations are such
objects to be held in the palm of the hand, which may be as to enable them to be retained in the extended position
hollowed into a cup or made to grasp a sphere. The with but a small expenditure of muscular power. As the
movements of the joints are indicated on the surface of weight of the body in the erect attitude falls behind the
the palm by tegumentary folds,—an oblique fold for the joints, the strong anterior fibres of their capsular liga-
thumb, and two oblique folds for the metacarpo-phalangeal ments are made tense, and the extended position of the
joints of the fingers; the joints of the second and third joints is preserved. So long as the centre of gravity falls
phalanges are also marked on the surface by folds. within the basis of support of the body, i.e., the space

between the two feet when standing on both legs, the body JOINTS AND MUSCLES OF THE LOWER LIMB.

will not fall. If the body is made to lean forward, then

the capsular ligament is no longer tense, and the glutæal The innominate bones are connected to the spinal column muscles are put in action to re-extend the trunk on the by the sacro-iliac joints and the sacro-sciatic ligaments. thigh, and prevent it from falling forward ; if the body is The Sacro-iliac Joint is between the side of the sacrum and made to lean to one side or the other, the round ligament the internal surface of the ilium, the articular surfaces of is made tense, or the strong ilio-tibial band of the fascia which bones are covered by cartilage, and connected lata of the thigh, which stretches from the ilium to the together by short, strong ligaments. The sacro-sciatic tibia, is put on the stretch, and falling sideways is preligaments stretch from the side of the sacrum and coccyx vented. When, in standing erect either on one or both to the spine and tuberosity of the ischium. The two feet, the balance of the body is disturbed, then various innominate bones are also connected together at the pubic muscles both of the trunk and lower limb are brought into symphysis, which is an amphiarthrodial joint. The sacrv action to assist in preserving the erect position. In the iliac joints and pubic symphysis permit only slight move erect position the weight of the trunk is transmitted ment; that at the former is around an imaginary axis, through the acetabula to the heads of the thigh-bones, but drawn transversely through the second sacral vertebra, which the position and connections of the round ligament enable allows the base of the sacrum to be thrown forward and its it to suspend that portion of the trunk the weight of which apex backward in the stooping position of the body; but is thrown upon it, and to distribute the weight over the too great movement backward of the apex is checked by head of the femur. the sacro-sciatic ligaments. As the weight of the trunk, The Knee is the largest and most complicated joint in Knee. or of what may be carried in the arms or on the back, is the body. It consists of the femur, tibia, and patella. transmitted through the haunch-bones to the lower limbs, | The patella moves up and down the trochlear surface of

Sacro-iliac joint.

the femur, whilst the condyles of the femur roll upon the exists between the astragalus and us calcis, between which
semilunar cartilages and articular surfaces of the tibia. bones a powerful interosseous ligament passes. Between
A powerful investing ligament encloses the articular sur the astragalus and scaphoid, and the os calcis and cuboid,
faces. This ligament is subdivided into bands, one on important diarthrodial joints are found, which are enclosed
each side of the joint—the internal and external lateral liga- by ligamentous bands. The remaining tarsal bones are
ments—a posterior and an anterior. The anterior extends connected together usually by dorsal, plantar, and inter-
from the patella to the anterior tubercle of the tibia, and osseous ligaments, and a similar mode of union is found
serves both as a ligament and as the tendon of insertion of between the distal row of tarsal bones and the metatarsals,
the extensor muscles of the leg. Within the investing except between the great toe and ento-cuneiform, where
ligament two interarticular or crucial ligaments pass from there is no interosseous ligament. The four outer meta-
the inter-condyloid fossa to the upper surface of the tibia; tarsals are also connected at their proximal ends by distal,
and interposed between the tibia and femoral condyles are plantar, and interosseous ligaments; and further, a trans-
two menisci, which from their shape are called the semi- verse metatarsal ligament passes between the distal ends
lunar cartilages. The synovial membrane not only lines of all the metatarsal bones. The metatarsal bones articu-
the investing ligaments, but covers the front of the femur late with the phalanges, and the phalanges with each other,
for some distance above the trochlea, and forms folds or in a similar manner to that described in the corresponding
pads within the joint itself, which in certain movements bones of the hand.
are interposed between the articular surfaces of the bones. At the ankle joint movements of flexion and extension
The movements at this joint are those of flexion and exten- | take place. The dorsum of the foot is bent towards the
sion. The flexors are the three great muscles on the back front of the leg by the direct action of the muscles on the
of the thigh, called the ham-strings; they all arise from front of the leg, more especially the tibialis anticus, inserted
the ischial tuberosity, and are inserted—the biceps into into the ento-cuneiform and metatarsal of great toe, and
the head of the fibula, the semi-tendinosus and semi-mem- the peroneus tertius, inserted into the metatarsal of little
branosus into the upper end of the tibia. The extensors toe; the opposite movement, the so-called extension of the
form the fleshy mass on the front and outer side of the foot, is due to the action of the gastrocnemius and soleus,
thigh; one muscle, the rectus, arises from the ilium—the the great muscles of the calf of the leg, which are inserted
others, the vasti, from the shaft of the femur; and they are by the Tendo Achillis into the posterior prominence of the
all inserted by a powerful tendon into the patella, and os calcis or heel This movement is made at every step in
through the anterior ligament of the knee into the tibia. walking or running, and the great size of the calf-muscles
The patella is indeed a sesamoid bone, developed in the is in relation to their use in the act of progression. The
tendon of these muscles (Fig. 18). The knee can be bent foot cannot, however, be drawn so far back as to be brought
so that the calf can touch the back of the thigh, and in into direct line with the leg. In standing erect the foot is
this position the patella is drawn down in front of the at right angles to the axis of the leg, the astragalus is
joint, as in kneeling. The articular surface of the patella locked in between the two malleoli, and the fibres of the
is divided into seven areas or facets, and in passing from lateral ligaments are tense, so as to check movement
the bent to the extended position of the joint, these facets forwards or backwards, and prevent displacement.
come successively into contact with the articular surface of Between the several bones of the tarsus a certain amount
the femur, until, when the leg is fully extended on the of gliding is permitted, more especially between the os
thigh, the whole of the patella is raised above the femoral calcis and cuboid and the astragalus and scaphoid, so that
trochlea, except the lowest pair of narrow facets. It is in it is possible to invert or evert the foot, i.e., to raise its
order to provide a smooth surface for the patella in this inner or outer borders from the ground. The inversion is
position that the synovial membrane of the joint covers performed by the tibialis anticus and by the tibialis
the front of the lower end of the femur. At the com- posticus, which latter is inserted into the scaphoid bone;
mencement of flexion a slight rotation inwards of the leg the eversion by the peroneus longus and brevis muscles,
and foot takes place through the action of the sartorius, situated on the outer side of the leg, the tendons of which
gracilis, and semi-tendinosus, which are inserted close pass behind the outer malleolus,—the brevis to be inserted
together into the tibia ; whilst the extensor muscles cause, into the metatarsal bone of the little toe, the longus into
at the completion of extension, a slight rotation outwards the plantar surface of the metatarsal bone of the great toe.
of the leg and foot. The movements of flexion and exten- The individual toes are bent on the sole by the action of
sion are not simply in the antero-posterior plane, but the flexor muscles inserted into the plantar surface of the
along oblique paths which are determined by the screwed phalanges, and they are straightened by the extensor
configuration of the femoral condyles. In complete exten- muscles inserted into their dorsal surfaces; the toes also
sion of the leg the joint is “screwed home;" and as this can be drawn asunder or abducted, and drawn together
position is necessary for the preservation of the erect or adducted, chiefly by the action of the interossei
attitude, the lateral, the posterior, and the anterior crucial muscles. The hallux or great toe is the most im-
ligaments are then all tense, to prevent displacement of portant digit; a line prolonged backwards through it to
the bones. The muscles which rotate the leg and foot the heel forms the proper axis of the foot, and the sole
inwards initiate the act of flexion by unlocking the joint. chiefly rests upon the pads of integument situated beneath

The Tibio-fibular Joints are found between the upper its metatarso-phalangeal joint and the heel. The hallux and lower ends of the bones, and in addition a strong is much more restricted in its movements than the thumb: interosseous membrane fills up the interval between their the configuration of its tarso-metatarsal joint and the shafts. The movement between the two bones is almost attachment of the transverse metatarsal ligament prevent inappreciable.

the great toe from being thrown across the surface of the Joints of The Ankle Joint is formed by the convex upper and the sole as the thumb is thrown across the palm in the moveankle and lateral surfaces of the astragalus fitting into the concavity ment of opposition; an object can, however, be grasped foot.

forried by the lower end of the tibia and the two malleoli. between the hallux and second toe by the action of its
An investing ligament, lined by synovial membrane, adductor muscles, and persons can be trained to write with
encloses the joint; the lateral portions of this ligament a pen or pencil held in this position.
forn distinct bands, and are much stronger than the The act of walking consists in the movement forwards
anterior and posterior fibres. A diarthrodial joint also of the trunk by the alternate advancement of the lower

I. - 106

limbs. Suppose a person to be standing erect, with one walls of the great visceral chambers,—the thorax and abdomen,leg a little in advance of the other; the body, being is marked off by the position and course of the intercostal series of

spinal nerves. inclined slightly forwards, is pushed in advance by the

The muscles of the appendicular skeleton are either limited to extension of the hindmost limb, so that the weight falls the limbs (purely appendicular, therefore), or pass from the axiai more and more upon the advanced leg, which at the same part of the body to the limb (axi-appendicular). The axi-appen. time is shortened by bending the knee and ankle. The dicular group are undoubtedly prolongations of the axial system of heel of the hindmosť limb being then raised by the action subdivision, and form the trapezius, rhomboid, levator anguli

muscles. They are in the upper limb derived from the epi-skeletal of the muscles of the calf, the toes press against the ground scapulæ, latissimus dorsi, serratus magnus, greater and smaller so as to push the trunk so far in front of the advanced pectorals, and subclavius muscles of each superior extremity. In limb as to be no longer safely supported by it; the hind the lower limb they are in part derived from the hypo-skeletal most limb is then raised from the ground by muscular glutæus maximus, from the epi-skeletal subdivision. It is not

subdivision, and form the psoas and pyriformis ; and in part, as the action, and allowed to swing forward by its own weight, improbable that the purely appendicular muscles are also prolonbut guided by the muscles, until the toes touch the ground gations of the axial system, and that as the limbs, in their developin front of the opposite limb. A step has now been made, ment from their fundamental bud-like lappets, undergo both a and the limbs are in a corresponding but oppositè position prolonged into them, differentiates both transversely and longifrom that in which they were when the step commenced : | tudinally into a motor apparatus, fitted for the performance of the a repetition of the act constitutes another step, and so the special functions of each extremity. alternate action continues. At one moment in each step both feet touch the ground at the same time, i.e., when

ANATOMY OF THE TEXTURES OR TISSUES. the hind foot presses against the earth. The act of running consists in a repetition of the movements of walking per

Introductory. formed with so much greater rapidity that the feet never touch the ground at the same moment; the heels also are Before proceeding to the description of the other organic never bronght to the ground. The propulsive action is systems of which the human body is built up, it may be also greatly increased by the extension of the hip and knee well to enter into the consideration of the minute or joints, so that a succession of small leaps on to alternate microscopic structure of its constituent parts. These parts feet takes place. In leaping from the standing position may primarily be divided into fluids and solids. The fluids the joints of both lower limbs, previously flexed, aresuddenly are the blood, the lymph, the chyle, the secretions of the and simultaneously extended, and the body is projected various glands, and of the serous and synovial membranes. forwards with a rapid impulse.

The solids form the framework of the several organic

systems, and assume different appearances in different Development and Homologies of the Voluntary Muscular System. localities. Sometimes they are arranged in compact solid

The voluntary muscles, like the bones and joints with which masses, as in cartilage; at others they are elongated into they are so intimately associated, are developed out of the middle fine threads or fibres, as in muscle, tendon, nerve; at of the three layers—the meso-blast-into which the germinal area or blastoderm of the young embryo is divided. The muscles of the fasciæ or aponeuroses, the serous, synovial, and mucous

others they are expanded into thin membranes, as in the axial skeleton are capable of subdivision into a group situated outside the eulo-skeleton, i.e., between it and the integument- membranes ; at others they are hollowed out into distinct which muscles have recently been called epi-skeletaland a group tubes for the conveyance of fluids, as in the blood-vessels, lying on the veatral surface of the vertebral bodies and within the the lymph and chyle vessels, and the ducts of glands. To rib arches, which have been termed the hæmal or hypo-skeletal the solids of the body, whatever their form may be, the muscles. The epi-skeletal muscles, like the vertebræ themselves, are developed within the proto-vertebræ, but it is not known if the general name of Tissues or Textures is applied. Each hypo-skeletal group have the same origin. In fishes the epi- organic system may be regarded as in the main composed skeletal muscles preserve their fundamental arrangement with but of a tissue or texture peculiar to and characteristic of itlittle modification. They are disposed in transverse segments or myotomes, which equal in number the vertebræ. These myotomes self. Thus, the bones are essentially composed of the are separated from each other by bands of fibrous tissue, the inter osseous tissue, the muscles of the muscular tissue, the muscular septu. In man and the higher vertebrates the simple nervous system of the nervous tissue, fibrous membranes of transversely segmented arrangement is to a large extent lost. Traces the fibrous or connective tissue, &c. But though the are preserved, however, in the interspinales and intertransversales essential constituent of each organic system is a tissue muscles, situated in the intervals between the spines and transverse processes of some of the vertebral segments ; in the external inter- peculiar to that system, yet in most localities certain other costals and in the recti abdominis muscles, in the last-named of tissues are mingled with that which is to be regarded as which tendinous bands subdivide the muscle into several transverse the characteristic texture of the part. In a muscle, for segments. More usually, the intermuscular septa either are not example, not only is the muscular tissue present, but continuous mass of muscle. In some instances the fibres of this mingled with it are connective tissue, nerve tissue, blood. muscle run longitudinally, and the entire mass subdivides longi- vessels, and lymph-vessels. A gland also not only consists tudinally into separate and distinct parallel muscles, as is seen in of its proper tissue, the secreting cells, but of more or less the subdivision of the great erector spinæ into the sacro-lumbalis,

connective tissue, nerves, blood and lymph vessels, and musculus accessorius, cervicalis ascendens, longissimus dorsi, transversalis cervicis, trachelo-mastoid, and spinalis dorsi muscles. In gland ducts. Indeed, there are few localities in which, other instances the muscles run obliquely ; some on the back of along with the proper tissue of the part, blood and lymph the body pass obliquely from below upwards and outwards, as the vessels, nerves and connective tissue, are not found; and to splenius and obliquus inferior ; others obliquely from below, upwards and inwards, as the complexus, obliquus superior, semi

a part built up of two or more tissues the name of an spinalis, multifidus and rotatores spinæ ; others again, as the external Organ is applied. Thus the muscular system consists of and internal oblique muscles of the abdomen, extend obliquely from the series of organs which we call the muscles, the glandbehind forwards to the ventral mesial line.

ular system of the several organs called glands, and so on. Of the hypo-skeletal group of muscles, the internal intercostals display the transverse segmentation. As a rule, however, the muscles that tissue enters as the characteristic texture, possesses

Each tissue and each organ, into the construction of which of this group extend longitudinally, and form the præ-vertebra. group, named anterior recti, longi colli, and psoæ ; though the diaphragm, not only distinctive structural, but also distinctive functional triangulares sterni, transversi abdominis, and levatores ani, which properties. Thus the muscular tissue is characterised by lie in relation to the inner surfaces of the ribs and visceral cavities, the property of contractility, and the muscles, of which are not longitudinal, but are specially modified in arrangement for functional reasons. The plane of demarcation between the hypo- it forms the essential texture, are organs of motion or end epi-skel-tal groups of muscles, where they form together the locomotion ; the osseous tissue is characterised hy its


hardness and strength, and the bones, of which it forms | body of a higher organism, he has given the general name
the essential texture, are organs of protection and support. of a Cytode. Sometimes a cytode is a naked clump of Cytode.

But the study of the textures embraces an inquiry not soft protoplasm, without a trace of differentiation either
only into the special, structural, and functional properties on its surface or in its substance, as in the freely-moving
of each tissue and organ-into the special part which each Monera ; at others the peripheral part of the cytode
plays in the animal economy—but the consideration of hardens, and differentiates into a more or less perfect
their properties as living structures. It would be out of envelope, as in the genera Protomonas and Protomyxa.
place in this article to enter into a discussion of the mean So far back as 1861, Lionel Beale had described, under
ing of the term LIFE, or LIVING, or to attempt an analysis the name of germinal matter (Bioplasm), minute living
of the vario's definitions of the term which have been particles of vegetable protoplasm, and in 1863 he demon-
suggested from time to time by different philosophers, strated the presence of extremely minute particles of living
which will naturally find a place in the article PhysIOLOGY. matter in the blood. More recently Stricker has also
It will suffice for our present purpose to adopt the old called attention, in the bodies of the higher animals, to
Aristotelian definition, and to speak of Life as the faculties minute detached clumps of protoplasm which exhibited
of self-nourishment, self-growth, and self-decay. All the the phenomena of life.
tissues, over and above the special properties which they As a rule, however, in both vegetable and animal Cell.
possess, have the power of growing and of maintaining organisms the specks or clumps of protoplasm assume
themselves in full structural perfection and functional definite shapes, and show evidence of an internal dif-
activity for a given period of time. After a time they ferentiation. In the midst of a minute clump of this
begin to exhibit signs of diminished perfection and activity, substance a sharply-defined body called a nucleus is
they degenerate or decay; ultimately they die, and the found, which differs from the surrounding protoplasm
entire organism of which they form the constituent parts in not being contractile; and sometimes a minute speck,
is resolved by the dutrefactive process into more simple or nucleolus, exists within the nucleus. When a definite
forms of matter.

clump of protoplasm contains a nucleus in its interior,

whether a nucleolus be present or not, it is called a GENERAL CONSIDERATIONS ON CELLS.

Nucleated Cell. Cells are definite anatomical and The simplest form of organic matter capable of ex- physiological units, and exhibit all the phenomena of hibiting the phenomena of life is called Cyto-blastema or life. Some of the lowest organisms consist merely of a Protoplasm. It possesses a viscous or jelly-like con- single cell, others of two or more cells united together, sistency. Under the highest powers of the microscope it and these are called uni- or multi-cellular organisms. seems to be homogeneous, or dimly granulated, like a Cells also enter in the most material manner into the sheet of ground glass. Not only can it assimilate nutri- constitution of the textures of all the higher forms of ment and increase in size, but it possesses the power plants and animals. Not unfrequently the peripheral of spontaneous movement and contractility. It enters in part of the protoplasm of the cell differentiates into a a very important manner into the structure of the bodies distinct investing envelope, technically named a cell wall of the lower animals. The elongated processes, or pseudo- or cell membrane. podia, to which Dujardin applied the

In the earlier periods of investigation into the minute name of sarcode, which the Rhizopoda

structure of cells it was believed that a cell wall was concan project from their surface into the

stantly present, and that each cell was a minute microsurrounding medium, and again with

scopic vesicle or bladder, which in its typical shape was draw into their substance, consist of

globular or ovoid, but capable of undergoing various modiprotoplasm, and may be cited as fur

fications both in form and chemical composition. The nishing excellent examples of its

material enclosed by the cell wall was termed the cell conmotive and contractile power. From

tents, and either in the midst of these contents or in conthe recent researches of Haeckel it

tact with the cell wall was the nucleus, which might or might would appear that protoplasm is

not contain a nucleolus. Schwann believed that the cell capable of forming, without the super. Fig. 25. — Undifferentiated

wall was the most active constituent of the cell, i.e., posaddition of any other structure, inde cytode mass of proto sessed the power not only of producing chemical and pendent organisms, which stand at


physical changes in its own substance and in the cell the lowest grade of organisation, and from their extreme contents, but of separating materials from the surrounding simplicity are named by him Monera.

media, -of secreting them, as it were, into the interior of Monera belong the genera Protamceba, Protogenes, and the cell. In this manner he accounted for the formation Bathybius. Of these, Bathybius is that

in some cells of fat, in others of pigment, in others of the which has attracted most attention. It has

characteristic secretion of glands, and so on. been regarded as a layer of soft slimy un

It was then maintained by John Goodsir that the differentiated protoplasm covering the bot

nucleus was the part of a cell which in all probability was tom of the deep sea, and capable of exhibit

concerned in separating and preparing its characteristic ing the phenomena of contractility, growth,

cell contents, and in its nutrition. Martin Barry and assimilation of food, and reproduction.

Goodsir also contended that the reproduction and multiDoubts, however, have been expressed re

plication of cells were due to self-division of the nucleus, garding the nature of this Bathybius, so

which was thus the source of successive broods of young that it cannot now be cited as so definite

cells. They gave to the nucleus, therefore, an importance an organism as the freely-swimming Pro- Fr. 26.-A simple in the economy of the cell greater than had previously tamoba and Protogenes. Haeckel has re

been assigned to it. ferred these simple organisms to a sub protoplasm cell As the investigations into cell structure became more kingdom of PROTISTÆ, which he considers

nucleus; M, nu

extended, it was ascertained that a cell wall was by no to lie on the confines of both the animal

means always present; that in many of the cells in which and vegetable kingdoms. To a mass of protoplasm, whether it had been supposed to exist it could not satisfactorily be it forms, as in one of these PROTISTÆ, an independent demonstrated, and that in others, more especially in young organism, or is merely a portion of the substance of the actively-growing cells, no trace of an investing envelope


To the group


form of cleated cell.


substance ;

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young cells.

could be observed Hence the importance of the cell wall as are descended from those produced by tne segmentation an essential component of a cell was still further diminished; of the yelk. The process of developinent of young cells and Leydig then defined a cell to be a little mass composed within a parent cell, whether it occurs in the ovum or in of a soft substance enclosing a central nucleus.

a cell derived by descent from the ovum, is called the But a most important advance in our conceptions endogenous reproduction of cells. But cells may multiply of the essential structure of a cell was made when by a process of fissioni.e., a constriction, gradually deepBrücke pointed out that the contents of cells not unfreening, may take place in a cell until it is subdivided into quently possessed the property of spontaneous move two; the nucleus at the same time participating in the ment and contractility, and when Max Schultze deter- constriction and subdivision. A third mode of multiplimined that the contractile substance termed sarcode, cation of cells is by budding : little clumps of protoplasm which forms so large a part of the bodies of the lower bud out from the protoplasm of the parent cell, become animals, was analogous and apparently homologous with detached, and assume an independent vitality. the contents of young actively-growing animal and vege- nucleus differentiates in the interior of such a clump, it table cells, before a differentiation of these contents into becomes a cell; if it remains as a mere clump of protospecial secretions or other materials had taken place. As plasm, it is a cytode. the term “protoplasm" had been introduced by Von Mohl These various methods of multiplication are all conto express the contents of the vegetable cell, which under- firmatory of Schwann's generalisation of the descent or goes changes in the process of growth, it was adopted by derivation of cells from pre-existing cells. But as the the animal histologist; and Max Schultze suggested nucleated cell, either with or without a cell wall, is not, in that a cell should be defined to be a nucleated mass the present state of science, regarded as the simplest and of protoplasm,-a definition which is adopted in this most elementary unit capable of exhibiting vital phenoarticle. Now, as protoplasm, whether it occurs along with mena, and as these phenomena can be displayed by india nucleus in the form of a cell, or in independent clumps vidual clumps of protoplasm, without the presence of a or cytodes, exhibits not merely the property of contrac- nucleus, some modification of the doctrine, as regards the tility, but the power of growing and maintaining itself, it formation of the tissues from nucleated cells, seems to be is regarded as the functionally active constituent of the necessary. For, although there can be no doubt that all cell. And thus our conceptions as to the part of the cell the tissues are mediately derived from the ovum or fundain which its functional activity resides have passed through mental cell, and that most of the tissues are derived three phases. In the first, the cell wall; in the second, the directly from nucleated cells, yet there is reason to think nucleus; in the third, the protoplasm cell contents, or cell that a differentiation of a cytode clump of protoplasm into substance, has been regarded as the active constituent, not tissue

may take place, so that the direct formation of such only as regards its nutrition, but the reproduction of a tissue would be, not from a nucleated cell, but from the

But though the protoplasm can of itself more simple cytode. Hence a more comprehensive gene perform these offices, yet there can be no doubt, as Barry ralisation, to which observers have gradually been led and Goodsir were the first to show, that the nucleus of the from the consideration of numerous facts, has now been cell plays a part not unfrequently in the multiplication of arrived at,—that the tissues and organs of the body, whatcells by self-division.

ever may be their form and composition, are formed of One of the most characteristic cells is the mammalian protoplasm, or produced by its differentiation; and that ovum. In it a cell wall exists, known

the protoplasm itself is derived by descent from the protoas the zona pellucida or vitelline

plasm substance of the primordial germ-cell. Some, inmembrane ; within this envelope is

deed, have contended that protoplasm, cells, and their the granular yelk or cell contents, N

derivatives can arise by a process of precipitation or in the midst of which is imbedded

aggregation of minute particles or molecules in an organic the nucleus or germinal vesicle, which

infusion, and that living matter may be thus spontanein its turn contains the nucleolus

ously generated. But the evidence which has been or germinal spot. The granules of F10 27. Ovum of a sheep.

advanced in support of this hypothesis is by no means the yelk are a special metamorphosis lucida ;?; protoplasm of satisfactory or conclusive, whilst the correctness of the of the protoplasm cell substance.

minal vesicle; Mi, nucleolus,

theory of the direct descent of protoplasm from pre-existSchwann made the important

or germinal spot.

ing living protoplasm is supported by thousands of generalisation that the tissues of the animal body observations made by the most competent inquirers. are composed of cells, or of materials derived from In the process of conversion of protoplasm into the cells, “ that there is one universal principle of develop- several tissues, there takes place a differentiation of form ment for the elementary part of organisms, however and structure (i.e., a morphological differentiation), and of different, and that this principle is the formation of composition (i.e., a chemical differentiation), as the result cells.” The ovum is the primordial or fundamental cell, or of which a physiological differentiation is occasioned, germ-cell, from which, after being fertilised by the male whereby tissues and organs are adapted to the performance sperm, the tissues and organs of the animal body are of special functions. Hence arise the several forms of derived. Within the fertilised ovum multiplication of tissue which occur in the human body and in the higher cells takes place with great rapidity. It is as yet an un animals. Many of the tissues consist exclusively of cells settled question how far the original nucleus of the ovum which present in different parts of the body characteristic participates in this process of multiplication ; but there modifications in external configuration, in composition, and can be no doubt that the protoplasm cell contents divide, in properties, as may be seen in the fatty tissue, pigmentary first into two, then four, then eight, then sixteen segments, tissue, and epithelium. Other tissues, again, consist partly and so on. Each of these segments of protoplasm con of cells, and partly of an intermediate material which sepatains a nucleus—is, in short, a nucleated cell, and the rates the constituent cells from each other. Here also the protoplasm of these cells exhibits the property of con cells present various modifications; and the intermediate tractility. The ovum or germ-cell is therefore the imme- material, termed the matrix or intercellular substance, diate parent of all the new cells which are formed within varies - in structure, in composition, and in properties it, and mediately it is the parent of all the cells which, in the different textures, as is seen in the connective, in the subsequent processes of development and growth, cartilaginous, osseous and muscular tissides




yelk; N, nucleus, or ger

Cell genesis.

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