THE MUSCULAR SYSTEM.
In all the Coelenterata, except the Ctenophora, the contractile
elements of the body wall consist of filiform processes of ectodermal
or entodermal epithelial cells (figs. 375 and 376 B). The elements
provided with these processes, which were first discovered by
Kleinenberg, are known as myoepithelial cells. Their contractile parts
may either be striated (fig. 376) or non-striated (fig. 375). In some
instances the epithelial part of the cell may nearly abort, its
nucleus alone remaining (fig. 376 A); and in this way a layer of
muscles lying completely below the surface may be established.
[FIG. 375. MYOEPITHELIAL CELLS OF HYDRA. (From Gegenbaur; after
Kleinenberg.)
_m._ contractile fibres.]
There is embryological evidence of the derivation of the voluntary
muscular system of a large number of types from myoepithelial cells of
this kind. The more important of these groups are the Chætopoda, the
Gephyrea, the Chætognatha, the Nematoda, and the Vertebrata[242].
[242] If recent statements of Metschnikoff are to be trusted, the
Echinodermata must be added to these groups. The amoeboid cells
stated in the first volume of this treatise to form the muscles
in this group, on the authority of Selenka, give rise, according
to Metschnikoff, only to the cutis, while the same naturalist
states the epithelial cells of the vaso-peritoneal vesicles are
provided with muscular tails.
While there is clear evidence that the muscular system of a large
number of types is composed of cells which had their origin in
myoepithelial cells, the mode of evolution of the muscular system of
other types is still very obscure. The muscles may arise in the embryo
from amoeboid or indifferent cells, and the Hertwigs[243] hold that in
many of these instances the muscles have also phylogenetically taken
their origin from indifferent connective-tissue cells. The subject is
however beset with very serious difficulties, and to discuss it here
would carry me too far into the region of pure histology.
[243] O. and R. Hertwig, _Die Coelomtheorie._ Jena, 1881.
_The voluntary muscular system of the Chordata._
The muscular fibres. The muscular elements of the Chordata undoubtedly
belong to the myoepithelial type. The embryonic muscle-cells are at
first simple epithelial cells, but soon become spindle-shaped: part of
their protoplasm becomes differentiated into longitudinally placed
striated muscular fibrils, while part, enclosing the nucleus, remains
indifferent, and constitutes the epithelial element of the cells. The
muscular fibrils are either placed at one side of the epithelial part
of the cell, or in other instances (the Lamprey, the Newt, the
Sturgeon, the Rabbit) surround it. The latter arrangement is shewn for
the Sturgeon in fig. 57.
[FIG. 376. MUSCLE-CELLS OF LIZZIA KÖLLIKERI. (From Lankester; after
O. and R. Hertwig.)
A. Muscle-cell from the circular fibres of the subumbrella.
B. Myoepithelial cells from the base of a tentacle.]
The number of the fibrils of each cell gradually increases, and the
protoplasm diminishes, so that eventually only the nucleus, or nuclei
resulting from its division, are left. The products of each cell
probably give rise, in conjunction with a further division of the
nucleus, to a primitive bundle, which, except in Amphioxus,
Petromyzon, etc., is surrounded by a special investment of sarcolemma.
The voluntary muscular system. For the purposes of description the
muscular system of the Vertebrata may conveniently be divided into two
sections, viz. that of the head and that of the trunk. The main part,
if not the whole, of the muscular system of the trunk is derived from
certain structures, known as the muscle-plates, which take their
origin from part of the primitive mesoblastic somites.
[FIG. 377. TRANSVERSE SECTION THROUGH THE TRUNK OF AN EMBRYO
SLIGHTLY OLDER THAN FIG. 28 E.
_nc._ neural canal; _pr._ posterior root of spinal nerve; _x._
subnotochordal rod; _ao._ aorta; _sc._ somatic mesoblast; _sp._
splanchnic mesoblast; _mp._ muscle-plate; _mp´._ portion of
muscle-plate converted into muscle; _Vr._ portion of the vertebral
plate which will give rise to the vertebral bodies; _al._ alimentary
tract.]
It has already been stated (pp. 292-296) that the mesoblastic somites
are derived from the dorsal segmented part of the primitive
mesoblastic plates. Since the history of these bodies is presented in
its simplest form in Elasmobranchii it will be convenient to commence
with this group. Each somite is composed of two layers--a somatic and
a splanchnic--both formed of a single row of columnar cells. Between
these two layers is a cavity, which is at first directly continuous
with the general body cavity, of which indeed it merely forms a
specialised part (fig. 377). Before long the cavity becomes however
completely constricted off from the permanent body cavity.
Very early (fig. 377) the inner or splanchnic wall of the somites
loses its simple constitution, owing to the middle part of it
undergoing peculiar changes. The meaning of the changes is at once
shewn by longitudinal horizontal sections, which prove (fig. 378) that
the cells in this situation (_mp´_) have become extended in a
longitudinal direction, and, in fact, form typical spindle-shaped
embryonic muscle-cells, each with a large nucleus. Every muscle-cell
extends for the whole length of a somite. The inner layer of each
somite, immediately within the muscle-band just described, begins to
proliferate, and produce a mass of cells, placed between the muscles
and the notochord (_Vr_). These cells form the commencing vertebral
bodies, and have at first (fig. 378) the same segmentation as the
somites from which they sprang.
After the separation of the vertebral bodies from the somites the
remaining parts of the somites may be called muscle-plates; since they
become directly converted into the whole voluntary muscular system of
the trunk (fig. 379, _mp_).
According to the statements of Bambeke and Götte, the Amphibians
present some noticeable peculiarities in the development of their
muscular system, in that such distinct muscle-plates as those of other
vertebrate types are not developed. Each side-plate of mesoblast is
divided into a somatic and a splanchnic layer, continuous throughout
the vertebral and parietal portions of the plate. The vertebral
portions (somites) of the plates soon become separated from the
parietal, and form independent masses of cells constituted of two
layers, which were originally continuous with the somatic and
splanchnic layers of the parietal plates (fig. 79). The outer or
somatic layer of the vertebral plates is formed of a single row of
cells, but the inner or splanchnic layer is made up of a kernel of
cells on the side of the somatic layer and an inner layer. The kernel
of the splanchnic layer and the outer or somatic layer together
correspond to a muscle-plate of other Vertebrata, and exhibit a
similar segmentation.
Osseous Fishes are stated to agree with Amphibians in the development
of their somites and muscular systems[244], but further observations
on this point are required.
[244] Ehrlich, "Ueber den peripher. Theil d. Urwirbel." _Archiv
f. mikr. Anat._, Vol. XI.
[FIG. 378. HORIZONTAL SECTION THROUGH THE TRUNK OF AN EMBRYO OF
SCYLLIUM CONSIDERABLY YOUNGER THAN 28 F.
_ch._ notochord; _ep._ epiblast; _Vr._ rudiment of vertebral body;
_mp._ muscle-plate; _mp´._ portion of muscle-plate already
differentiated into longitudinal muscles.]
In Birds the horizontal splitting of the mesoblast extends at first to
the dorsal summit of the mesoblastic plates, but after the isolation
of the somites the split between the somatic and splanchnic layers
becomes to a large extent obliterated, though in the anterior somites
it appears in part to persist. The somites on the second day, as seen
in a transverse section (fig. 115, _P.v._), are somewhat quadrilateral
in form but broader than they are deep.
Each at that time consists of a somewhat thick cortex of radiating
rather granular columnar cells, enclosing a small kernel of spherical
cells. They are not, as may be seen in the above figure, completely
separated from the ventral (or lateral as they are at this period)
parts of the mesoblastic plate, and the dorsal and outer layer of the
cortex of the somites is continuous with the somatic layer of
mesoblast, the remainder of the cortex, with the central kernel, being
continuous with the splanchnic layer. Towards the end of the second
and beginning of the third day the upper and outer layer of the
cortex, together probably with some of the central cells of the
kernel, becomes separated off as a muscle-plate (fig. 116). The
muscle-plate when formed (fig. 117) is found to consist of two layers,
an inner and an outer, which enclose between them an almost
obliterated central cavity; and no sooner is the muscle-plate formed
than the middle portion of the inner layer becomes converted into
longitudinal muscles. The avian muscle-plates have, in fact, precisely
the same constitution as those of Elasmobranchii. The central space is
clearly a remnant of the _vertebral portion of the body cavity_,
which, though it wholly or partially disappears in a previous stage,
reappears again on the formation of the muscle-plate.
The remainder of the somite, after the formation of the muscle-plate,
is of very considerable bulk; the cells of the cortex belonging to it
lose their distinctive characters, and the major part of it becomes
the vertebral rudiment.
In Mammalia the history appears to be generally the same as in
Elasmobranchii. The split which gives rise to the body cavity is
continued to the dorsal summit of the mesoblastic plates, and the
dorsal portions of the plates with their contained cavities become
divided into somites, and are then separated off from the ventral. The
later development of the somites has not been worked out with the
requisite care, but it would seem that they form somewhat cubical
bodies in which all trace of the primitive slit is lost. The further
development resembles that in Birds.
The first changes of the mesoblastic somites and the formation of the
muscle-plates do not, according to existing statements, take place on
quite the same type throughout the Vertebrata, yet the comparison
which has been instituted between Elasmobranchs and other Vertebrates
appears to prove that there are important common features in their
development, which may be regarded as primitive, and as having been
inherited from the ancestors of Vertebrates. These features are (1)
the extension of the body cavity into the vertebral plates, and
subsequent enclosure of this cavity between the two layers of the
muscle-plates; (2) the primitive division of the vertebral plate into
an outer (somatic) and an inner (splanchnic) layer, and the formation
of a large part of the voluntary muscular system out of the inner
layer, which in all cases is converted into muscles earlier than the
outer layer.
The conversion of the muscle-plates into muscles. It will be
convenient to commence this subject with a description of the changes
which take place in such a simple type as that of the Elasmobranchii.
[FIG. 379. SECTION THROUGH THE TRUNK OF A SCYLLIUM EMBRYO SLIGHTLY
YOUNGER THAN 28 F.
_sp.c._ spinal canal; _W._ white matter of spinal cord; _pr._
posterior nerve-roots; _ch._ notochord; _x._ subnotochordal rod;
_ao._ aorta; _mp._ muscle-plate; _mp´._ inner layer of muscle-plate
already converted into muscles; _Vr._ rudiment of vertebral body;
_st._ segmental tube; _sd._ segmental duct; _sp.v._ spiral valve;
_v._ subintestinal vein; _p.o._ primitive generative cells.]
At the time when the muscle-plates have become independent structures
they form flat two-layered oblong bodies enclosing a slit-like central
cavity (fig. 379, _mp_). The outer or somatic wall is formed of simple
epithelial-like cells. The inner or splanchnic wall has however a
somewhat complicated structure. It is composed dorsally and ventrally
of a columnar epithelium, but in its middle portion of the
muscle-cells previously spoken of. Between these and the central
cavity of the plates the epithelium forming the remainder of the layer
commences to insert itself; so that between the first-formed muscle
and the cavity of the muscle-plate there appears a thin layer of
cells, not however continuous throughout.
When first formed the muscle-plates, as viewed from the exterior, have
nearly straight edges; soon however they become bent in the middle, so
that the edges have an obtusely angular form, the apex of the angle
being directed forwards. They are so arranged that the anterior edge
of the one plate fits into the posterior edge of the one in front. In
the lines of junction between the plates layers of connective-tissue
cells appear, which form the commencements of the intermuscular septa.
The growth of the plates is very rapid, and their upper ends soon
extend to the summit of the neural canal, and their lower ones nearly
meet in the median ventral line. The original band of muscles, whose
growth at first is very slow, now increases with great rapidity, and
forms the nucleus of the whole voluntary muscular system (fig. 380,
_mp´_). It extends upwards and downwards by the continuous conversion
of fresh cells of the splanchnic layer into muscle-cells. At the same
time it grows rapidly in thickness by the addition of fresh
spindle-shaped muscle-cells from the _somatic layer_ as well as by the
division of the already existing cells.
_Thus both layers of the muscle plate are concerned in forming the
great longitudinal lateral muscles, though the splanchnic layer is
converted into muscles very much sooner than the somatic_[245].
[245] The brothers Hertwig have recently maintained that only the
inner layer of the muscle-plates is converted into muscles. In
the Elasmobranchs it is easy to demonstrate the incorrectness of
this view, and in Acipenser (_vide_ fig. 57, _mp_) the two layers
of the muscle-plate retain their original relations after the
cells of both of them have become converted into muscles.
Each muscle-plate is at first a continuous structure, extending from
the dorsal to the ventral surface, but after a time it becomes divided
by a layer of connective tissue, which becomes developed nearly on a
level with the lateral line, into a dorso-lateral and a ventro-lateral
section. The ends of the muscle-plates continue for a long time to be
formed of undifferentiated columnar cells. The complicated outlines of
the intermuscular septa become gradually established during the later
stages of development, causing the well-known appearances of the
muscles in transverse sections, which require no special notice here.
The muscles of the limbs. The limb muscles are formed in
Elasmobranchii, coincidently with the cartilaginous skeleton, as two
bands of longitudinal fibres on the dorsal and ventral surfaces of the
limbs (fig. 346). The cells, from which these muscles originate, are
derived from the muscle-plates. When the ends of the muscle-plates
reach the level of the limbs they bend outwards and enter the tissue
of the limbs (fig. 380). Small portions of several muscle-plates
(_m.pl_) come in this way to be situated within the limbs, and are
very soon segmented off from the remainder of the muscle-plates. The
portions of the muscle-plates thus introduced soon lose their original
distinctness. There can however be but little doubt that they supply
the tissue for the muscles of the limbs. The muscle-plates themselves,
after giving off buds to the limbs, grow downwards, and soon cease to
shew any trace of having given off these buds.
[FIG. 380. TRANSVERSE SECTION THROUGH THE ANTERIOR PART OF THE TRUNK
OF AN EMBRYO OF SCYLLIUM SLIGHTLY OLDER THAN FIG. 29 B.
The section is diagrammatic in so far that the anterior nerve-roots
have been inserted for the whole length; whereas they join the
spinal cord halfway between two posterior roots.
_sp.c._ spinal cord; _sp.g._ ganglion of posterior root; _ar._
anterior root; _dn._ dorsally directed nerve springing from
posterior root; _mp._ muscle-plate; _mp´._ part of muscle-plate
already converted into muscles; _m.pl._ part of muscle-plate which
gives rise to the muscles of the limbs; _nl._ nervus lateralis;
_ao._ aorta; _ch._ notochord; _sy.g._ sympathetic ganglion; _ca.v._
cardinal vein; _sp.n._ spinal nerve; _sd._ segmental (archinephric)
duct; _st._ segmental tube; _du._ duodenum; _pan._ pancreas; _hp.d._
point of junction of hepatic duct with duodenum; _umc._ umbilical
canal.]
In addition to the longitudinal muscles of the trunk just described,
which are generally characteristic of Fishes, there is found in
Amphioxus a peculiar transverse abdominal muscle, extending from the
mouth to the abdominal pore, the origin of which has not been made
out.
It has already been shewn that in all the higher Vertebrata
muscle-plates appear, which closely resemble those in Elasmobranchii;
so that all the higher Vertebrata pass through, with reference to
their muscular system, a fish-like stage. The middle portion of the
inner layers of their muscle-plates becomes, as in Elasmobranchii,
converted into muscles at a very early period, and the outer layer for
a long time remains formed of indifferent cells. That these
muscle-plates give rise to the main muscular system of the trunk, at
any rate to the episkeletal muscles of Huxley, is practically certain,
but the details of the process have not been made out.
In the Perennibranchiata the fish-like arrangement of muscles is
retained through life in the tail and in the dorso-lateral parts of
the trunk. In the tail of the Amniotic Vertebrata the primitive
arrangement is also more or less retained, and the same holds good for
the dorso-lateral trunk muscles of the Lacertilia. In the other
Amniota and the Anura the dorso-lateral muscles have become divided up
into a series of separate muscles, which are arranged in two main
layers. It is probable that the intercostal muscles belong to the same
group as the dorso-lateral muscles.
The abdominal muscles of the trunk, even in the lowest Amphibia,
exhibit a division into several layers. The recti abdominis are the
least altered part of this system, and usually retain indications of
the primitive intermuscular septa, which in many Amphibia and
Lacertilia are also to some extent preserved in the other abdominal
muscles.
In the Amniotic Vertebrates there is formed underneath the vertebral
column and the transverse processes a system of muscles, forming part
of the hyposkeletal system of Huxley, and called by Gegenbaur the
subvertebral muscles. The development of this system has not been
worked out, but on the whole I am inclined to believe that it is
derived from the muscle-plates. Kölliker, Huxley and other
embryologists believe however that these muscles are independent of
the muscle-plates in their origin.
Whether the muscle of the diaphragm is to be placed in the same
category as the hyposkeletal muscles has not been made out.
It is probable that the cutaneous muscles of the trunk are derived
from the cells given off from the muscle-plates. Kölliker however
believes that they have an independent origin.
The limb-muscles, both extrinsic and intrinsic, as may be concluded
from their development in Elasmobranchii, are derived from the
muscle-plates. Kleinenberg found in Lacertilia a growth of the
muscle-plates into the limbs, and in Amphibia Götte finds that the
outer layer of the muscle-plates gives rise to the muscles of the
limbs.
In the higher Vertebrata on the other hand the entrance of the
muscle-plates into the limbs has not been made out (Kölliker). It
seems therefore probable that by an embryological modification, of
which instances are so frequent, the cells which give rise to the
muscles of the limbs in the higher Vertebrata can no longer be traced
into a direct connection with the muscle-plates.
_The Somites and muscular system of the head._
The extension of the somites to the anterior end of the body in
Amphioxus clearly proves that somites, similar to those of the trunk,
were originally present in a region, which in the higher Vertebrata
has become differentiated into the head. In the adult condition no
true Vertebrate exhibits indications of such somites, but in the
embryos of several of the lower Vertebrata structures have been found,
which are probably equivalent to the somites of the trunk: they have
been frequently alluded to in the previous chapters of this volume.
These structures have been most fully worked out in Elasmobranchii.
The mesoblast in Elasmobranch embryos becomes first split into somatic
and splanchnic layers in the region of the head; and between these
layers there are formed two cavities, one on each side, which end in
front opposite the blind anterior extremity of the alimentary canal;
and are continuous behind with the general body-cavity (fig. 20 A,
_vp_). I propose calling them the head-cavities. The cavities of the
two sides have no communication with each other.
Coincidently with the formation of an outgrowth from the throat to
form the first visceral cleft, the head-cavity on each side becomes
divided into a section in front of the cleft and a section behind the
cleft; and at a later period it becomes, owing to the formation of a
second cleft, divided into three sections: (1) a section in front of
the first or hyomandibular cleft; (2) a section in the hyoid arch
between the hyomandibular cleft and the hyobranchial or first
branchial cleft; (3) a section behind the first branchial cleft.
The front section of the head-cavity grows forward, and soon becomes
divided, without the intervention of a visceral cleft, into an
anterior and posterior division. The anterior lies close to the eye,
and in front of the commencing mouth involution. The posterior part
lies completely within the mandibular arch.
As the rudiments of the successive visceral clefts are formed, the
posterior part of the head-cavity becomes divided into successive
sections, there being one section for each arch. Thus the whole
head-cavity becomes on each side divided into (1) a premandibular
section; (2) a mandibular section (_vide_ fig. 29 A, _pp_); (3) a
hyoid section; (4) sections in each of the branchial arches.
[FIG. 381. TRANSVERSE SECTION THROUGH THE FRONT PART OF THE HEAD OF
A YOUNG PRISTIURUS EMBRYO.
The section, owing to the cranial flexure, cuts both the fore- and
the hind-brain. It shews the premandibular and mandibular
head-cavities 1_pp_ and 2_pp_, etc. The section is moreover somewhat
oblique from side to side.
_fb._ fore-brain; _l._ lens of eye; _m._ mouth; _pt._ upper end of
mouth, forming pituitary involution; 1_ao._ mandibular aortic arch;
1_pp._ and 2_pp._ first and second head-cavities; 1_vc._ first
visceral cleft; _V._ fifth nerve; _aun._ auditory nerve; _VII._
seventh nerve; _aa._ dorsal aorta; _acv._ anterior cardinal vein;
_ch._ notochord.]
The first of these divisions forms a space of a considerable size,
with epithelial walls of somewhat short columnar cells (fig. 381,
1_pp_). It is situated close to the eye, and presents a rounded or
sometimes a triangular figure in section. The two halves of the cavity
are prolonged ventralwards, and meet below the base of the fore-brain.
The connection between them appears to last for a considerable time.
These two cavities are the only parts of the body-cavity within the
head which unite ventrally. The section of the head-cavity just
described is so similar to the remaining sections that it must be
considered as serially homologous with them.
The next division of the head-cavity, which from its position may be
called the mandibular cavity, presents a spatulate shape, being
dilated dorsally, and produced ventrally into a long thin process
parallel to the hyomandibular gill-cleft (fig. 20, _pp_). Like the
previous space it is lined by a short columnar epithelium.
[FIG. 382. HORIZONTAL SECTION THROUGH THE PENULTIMATE VISCERAL ARCH
OF AN EMBRYO OF PRISTIURUS.
_ep._ epiblast; _vc._ pouch of hypoblast which will form the walls
of a visceral cleft; _pp._ segment of body-cavity in visceral arch;
_aa._ aortic arch.]
The mandibular aortic arch is situated close to its inner side (fig.
381, 2_pp_). After becoming separated from the lower part (Marshall),
the upper part of the cavity atrophies about the time of the
appearance of the external gills. Its lower part also becomes much
narrowed, but its walls of columnar cells persist. The outer or
somatic wall becomes very thin indeed, the splanchnic wall, on the
other hand, thickens and forms a layer of several rows of elongated
cells. In each of the remaining arches there is a segment of the
original body-cavity fundamentally similar to that in the mandibular
arch (fig. 382). A dorsal dilated portion appears, however, to be
present in the third or hyoid section alone (fig. 20), and even there
disappears very soon, after being segmented off from the lower part
(Marshall). The cavities in the posterior parts of the head become
much reduced like those in its anterior part, though at rather a later
period.
It has been shewn that the divisions of the body-cavity in the head,
with the exception of the anterior, early become atrophied, _not so
however their walls_. The cells forming the walls both of the dorsal
and ventral sections of these cavities become elongated, and finally
become converted into muscles. Their exact history has not been
followed in its details, but they almost unquestionably become the
musculus constrictor superficialis and musculus interbranchialis[246];
and probably also musculus levator mandibuli and other muscles of the
front part of the head.
[246] _Vide_ Vetter, "Die Kiemen und Kiefermusculatur d. Fische."
_Jenaische Zeitschrift_, Vol. VII.
The anterior cavity close to the eye remains unaltered much longer
than the remaining cavities.
Its further history is very interesting. In my original account of
this cavity (No. 292, p. 208) I stated my belief that its walls gave
rise to the eye-muscles, and the history of this process has been to
some extent worked out by Marshall in his important memoir (No. 509).
Marshall finds that the ventral portion of this cavity, where its two
halves meet, becomes separated from the remainder. The eventual fate
of this part has not however been followed. Each dorsal section
acquires a cup-like form, investing the posterior and inner surface of
the eye. The cells of its outer wall subsequently give rise to three
sets of muscles. The middle of these, partly also derived from the
inner walls of the cup, becomes the rectus internus of the eye, the
dorsal set forms the rectus superior, and the ventral the rectus
inferior. The obliquus inferior appears also to be in part developed
from the walls of this cavity.
Marshall brings evidence to shew that the rectus externus (as might be
anticipated from its nerve supply) has no connection with the walls of
the premandibular head-cavity, and finds that it arises close to the
position originally occupied by the second and third cavities.
Marshall has not satisfactorily made out the mode of development of
the obliquus superior.
The walls of the cavities, whose history has just been recorded, have
definite relations with the cranial nerves, an account of which has
already been given at p. 461.
Head-cavities, in the main similar to those of Elasmobranchii, have
been found in the embryo of Petromyzon (fig. 45, _hc_), the Newt
(Osborn and Scott), and various Reptilia (Parker).
BIBLIOGRAPHY.
(507) G. M. Humphry. "Muscles in Vertebrate Animals." _Journ. of Anat.
and Phys._, Vol. VI. 1872.
(508) J. Müller. "Vergleichende Anatomie d. Myxinoiden. Part I.
Osteologie u. Myologie." _Akad. Wiss._, Berlin, 1834.
(509) A. M. Marshall. "On the head cavities and associated nerves of
Elasmobranchs." _Quart. J. of Micr. Science_, Vol. XXI. 1881.
(510) A. Schneider. "Anat. u. Entwick. d. Muskelsystems d.
Wirbelthiere." _Sitz. d. Oberhessischen Gesellschaft_, 1873.
(511) A. Schneider. _Beiträge z. vergleich. Anat. u. Entwick. d.
Wirbelthiere._ Berlin, 1879.
_Vide_ also Götte (No. 296), Kölliker (No. 298), Balfour (No. 292),
Huxley, etc.