scarcely distinguishable from the mass of the
body. While in these Ccelclmintha (or hollow
Nematoid worms), it is suspended from the
wall of the belly by filamentous processes. And
though such an acquisition of an abdominal
cavity is no doubt partly referrible to the isola-
tion demanded by the organs of locomotion,
yet not only does this itself imply a genera!
'advance of development, but it is actually
accompanied by a curious structure, which is
apparently connected with nutrition, and pos-
sibly renders the cavity of the abdomen the
receptacle of a kind of chyle. Its more perfe:t
form in the Ascaris lumbricoides may be briefly
described as consisting of a series of pyriform
processes, the peduncles of which are seated
immediately upon the mesenteric filaments
previously alluded to, and which project freely
into the abdominal cavity, so as to be sur-
rounded by the serum and grey transparent
substance that fills this space. Their shape
resembles that of the villi of higher animals;
and their size increases towards the median
line of the body.
The alimentary canal of the Polyp exhibits
so wide a range of development, that while
by one extreme it approaches that of the sim-
plest anenterous Infusoria, by the other it
attains a complexity akin to that of the highest
Invertebrate.
The Hydra is little more than a stomach or
sac, fixed by a sucker at its closed extre-
mity, and having at its other end a mouth sur-
rounded by prehensile tentacles. Digestion
is, however, energetic. The living prey, which
is paralysed by the deadly grasp of the ten-
tacles, undergoes a rapid solution in this sto-
mach, while its colours often visibly mix with
those of the parietes common to the organ
and theanimal; and finally, its excrementitious
residue is speedily rejected by the same orifice
through which it previously entered.
In other solitary Polyps for example in the
marine Actinice the folded bag formed by
the stomach is separated from the mouth
by an oesophageal constriction. It is at the
same time attached to, and isolated from, the
general wall of the animal, by radiating mus-
cular bands ; which extend vertically down the
whole depth of the organ, so as to resemble
the septa of a poppy capsule as seen in a
transverse section.
The compound Polyp appears chiefly to
vary from this type by virtue of its individuals
possessing a common stem, the proper nutri-
tion of which requires it to be closely con-
nected with the organ of digestion. Thus,
in some of the Antkozca which possess a
stomach very similar to that of the Sea-ane-
mones just described, an orifice of small size
at the bottom of the gastric sac seems to admit
the results of digestion into the general cavity
of the animal, within which they experience a
kind of circulation.
In the Tubularian Polyp, the canal is modi-
fied by the addition of a structure which may
be regarded as a pharyngeal proboscis. It is
a globular projection, surrounded by tentacles
at its free extremity, and by its other end
received immediately within a circle of simi-
lar organs; the place of its attachment being
marked by an internal constriction, through
which the cavity of this appendix communi-
cates with that of the stomach.
In many of these Polyps, the stomach
has been seen to possess a ciliated lining ;
and there are grounds for presuming the ex-
istence of a similar structure in several other
STOMACH AND INTESTINE.
297
species. Some of the circulatory movements
observed in their ingesta are perhaps accom-
plished by the aid of such an apparatus. While
their vigorous and almost peristaltic character
in other instances is due to structures, the
voluntary and powerful contractions of which
entitle them to rank as muscles.
The cilio-brachiate Polyp possesses an ab-
dominal cavity occupied by fluid, in which the
alimentary canal is free to move. The canal
itself has a mouth and anus, which are both
situated at the free extremity of the animal ;
the former orifice being within, the latter
without, its whorl of tentacles. The mouth
opens into a pharyngeal dilatation, from which
a narrow tube leads into an organ analogous to
a gizzard. This organ possesses radiating
muscular fibres, and rhomboidal teeth, that are
capable of crushing its contents. Immediately
beneath it is the stomach, in shape like a two-
necked flask, and having its blind extremity
fixed to the attached base of the animal by
a retractory muscle. The pyloric aperture
is guarded* by cilia, which rotate, and thus
delay, the food. The intestine is narrow and
simple, and its excrementitious contents are
expelled from the anus, to be immediately
hurried away by the current arising from the
action of the neighbouring cilia.
The body of the Acalcphcc generally con-
stitutes a disc with a fringed margin. It is
convex above, and concave below, with large
dependent processes. And it swims by what
seems to be an alternate preponderance
of contraction in these two surfaces.
The condition of the alimentary canal is
here very remarkable. The Entozoa have
already offered us a ramified tube, that
could scarcely be regarded as strictly diges-
tive. But these Sea-nettles further com-
plicate this branched state by the posses-
sion of a central cavity. This is sometimes
placed between a convergent and a divergent
set of anastomosing canals ; and sometimes
approaches the stomach of the Distoma in
possessing the latter set only. In the latter
case, the so-called stomach communicates,
by a short and simple tube, with the centre
of the lower or concave surface. And in
one species it also radiates unbranched tubes
which open on the margin of the disc.
The movements of the contents of these
canals seem to be effected by cilia. The
ramifications of the canals chiefly occupy the
under surface of the animal.
The large order of Echinodcrmata again
presents us with an important advance of
development in passing from its lowest to
its highest members.
Thus the alimentary canal of the Asterias
has a single aperture on the under surface
of the animal. This leads by a short tube to
a central cavity, which divides into two pro-
cesses for each ray. These processes give off
secondary branches at right angles to them-
selves, and the latter end in tertiary caeca. In
Coma tula the caeca disappear, and the canal
acquires a distinct mouth and anus, which open
near each other. In all, the canal is muscular,
is enclosed in a ciliated peritoneum, and has
its primary divisions attached by a kind of
mesentery.
In the Echinus, the anus generally opens on
the upper or opposite surface of the body.
Many of this genus have a complex masti-
catory organ, which is acted upon by powerful
muscles. The first part of the canal opens
into an intestine of much larger diameter,
opposite to a blind dilatation very like the
human caecum. The intestine is coiled twice
around the inner surface of the shell ; the
second coil reversing the direction taken by
the first, and both exhibiting a sinuous course.
Its width tapers away to the anus. Its struc-
ture is delicate and transparent; it possesses a
mucous membrane, and longitudinal and trans-
verse fibres ; and it exhibits an intestinal vein,
which is especially marked towards the termi-
nation of the canal.
In the vermiform Holothimee the canal
forms a kind of Z in the abdominal cavity;
passing first backwards, then forwards, and
again backwards to its posterior extremity.
The first part is wider and stronger than the
rest, and its more glandular mucous membrane
presents longitudinal folds which terminate
in a slight circular one. Such a structure
causes this dilatation to be regarded as a
stomach. The narrowing intestine often ter-
minates in a large oval cloaca, into which
open two branching caeca.*
The Annelida form a class of animals so
diverse in nature and structure, that it is diffi-
cult to include all the varieties of their diges-
tive apparatus within a mere brief sketch. The
canal always possesses a distinct mouth and
anus, which occupy the opposite ends of the
more or less elongated and cylindrical body.
Prehension is generally aided by teeth, which,
as in the Leech, perforate the skin of their
prey; while in others as in some of the
Errantes it is effected solely by a proboscis.
In many of the marine Errantes the intes-
tinal canal is simple. In the Lumbrici the
canal soon dilates into a membranous pouch,
which is followed by a thicker and more
muscular portion, supposed to be a gizzard.
In some genera, this part of the tube is com-
plicated by being produced into pouches.
These are either numerous, as in the Leech;
or few, as in some kindred genera. Fi-
nally, in the Earth-worm, they are reduced
to mere constrictions of the canal ; while in
the Aphrodita, they are developed into tubes,
which expand, divide, and terminate as al-
most globular pouches. Clusters of glandular
follicles, which are supposed to be biliary,
open into the posterior half of the complicated
canal of the leech just alluded to : and analo-
gous structures are found in other genera.
In the Earth-worm, there is a singular ap-
paratus, the typhhtote. This is a blind tube,
which occupies almost the whole length of the
canal, being attached to its dorsal aspect, and
* Such a complex organization is strangely con-
trasted with the alleged fact, thai the animal, when
alarmed, can shed the -whole canal. This extraor-
dinary act is presumed to be voluntary, and is only
paralleled by the growth of another digestive ap"-
paratus, which replaces that evacuated.
298
STOMACH AND INTESTINE.
projecting into its cavity. Its interior surface
is folded and villous. The whole structure
appears to be connected with a kind of chy-
lous absorption.
The alimentary canal of the Epizoa differs
from that of the cavitary Entozaa, in being
generally surrounded by a glandular mass, the
function of which is probably hepatic. The
Cirripeda have prehensile jaws, and a ter-
minal mouth and anus. In some, the canal
has a gastric dilatation. Hepatic follicles,
similar to those already described, occur here
also. And St. Ange and Serres have found a
tube analogous to the typhlosole.
The digestive tube of the Crustacea may
be reduced to two chief forms, which corre-
spond with other differences in the nature and
structure of their possessors. Thus in those
lower Crustaceans which are suctorial and para-
sitic, the canal is a very simple one. A proboscis
conceals a pair of lancet teeth, and is followed
by a straight intestine, around which are
clustered a dense mass of follicles, supposed
to constitute a liver. The higher Crustaceans
possess a complicated apparatus of forceps
and jaws. A short oesophagus leads to a
large spherical cavity, which occupies the head
of the animal, and which, although sometimes
called a stomach, contains hard structures
that render it analogous to a gizzard. A well-
marked constriction separates this organ from
the intestine, which is sometimes simple and
nearly straight, sometimes divided into two
portions distinguished by a projecting valve.
The liver is conglomerate, and divided into
lobules. Rarely, one or two caecal tubes are
also present.
The alimentary canal of the Insect offers
what are rather varieties of development
than any regular transition, such as we have
remarked in some of the preceding orders:
varieties which the metamorphosis of the larva
at present seems to complicate instead of ex-
plain.
In the larva, the canal is comparatively
simple, and somewhat approaches the condi-
tion seen in the lower Annelida : being a straight
tube, with a mouth and anus at opposite ends
of the body. In many Hymenopterous larvae,
the latter aperture is absent, In others it is
only developed towards the end of this stage
of life, when an excrement or meconium as
we may perhaps call it is for the first time
expelled. But though such an intestine
might seem to resemble that of the anen-
terous Infusory, or the hydriform Polyp, we
must recollect that it differs from these in the
important fact of its not being used for the
double purpose of ingestion and egestion.
The complications of the above simple canal
relate chiefly to its subdivision, and to the addi-
tion of blind tubes. A gastric dilatation is the
first to appear ; its extremities then become
constricted, and its calibre enlarged. An oeso-
phagus, a crop or ingluvies, a small and a large
intestine, may also be added. Sometimes the
supposed stomach is transversely divided into
two cavities, and complicated by short caeca.
In other instances, longer tubes open into the
same part of the canal. While in others, they
open into the intestine below this point; and
are hence presumed to be biliary.
In the perfect Insect the varieties of form
are still more numerous and perplexing.
Besides the complicated prehensile and dental
apparatus, there is often an oesophagus, a crop, a
muscular gizzard, a stomach, a small intestine,
a large intestine, and a narrower rectum. But
development is manifested, not only by differ-
ences in the diameter and structure of dif-
ferent lengths of the tube itself, but also by its
complication, through the addition of supple-
mentary organs of a more or less tubular form.
The ingluvies or crop is present in many
but not all of the suctorial genera. It is
sometimes distinctly glandular. And even
where, as in the Bee, this character is less
prominent, it is still probably a secreting organ.
But its uses seem to be mainly those of accu-
mulation.
The gizzard is generally added to the former
organ. It is characterized by distinct mus-
cularity, and a more or less hard or horny
epithelium, which is often developed into
plates, protuberances, hairs, or teeth. Some-
times it is only rudimentary: a toothed
oesophagus subserving its functions in some
insects ; while in others, it is reduced to a
mere thickening of the muscular wall of this
part of the canal.
The stomach is also of various form and
size. In some insects it is simple ; in others
it is more or less plicated or cellulated, or
its cells are even prolonged into short caeca.
The peculiarities of the remaining subdivi-
sions of the canal are chiefly those of their
length and width, and in the degrees of con-
striction by which they are separated from each
other. As yet, however, it has been found im-
possible to make out any intimate connection
between these differences in the anatomy of
the tube and the habits of the animal possess-
ing it. Indeed, the general relations of this
kind seen in other orders often seem to be
interrupted or even reversed in the insects.
The numerous tubes which open into
the intestinal canal present still more diver-
sity. They are often named salivary, biliary,
or urinary organs. Thus those tubes which
open into the earlier part of the intestinal
cavity are called salivary ; those which empty
themselves into the commencement of the small
intestine are regarded as biliary; and, finally,
those which open into the canal at or near its
termination, are considered urinary. It is
only the first of these that, after many grada-
tions, fairly attain the glandular development
which a conglomerate condition implies. The
second vary chiefly in number, and in the fre-
quency of their anastomosis. The third
are rarely vesicular in shape.
The digestive canal of the Arachnida offers,
on the whole, more uniformity. The chief
divisions of this order are the parasitic, the
spiders, and the scorpions. All are " carni-
vorous :" a term which here, as often else-
where, is only approximative^ correct; since
most of them do not devour the flesh, but
STOMACH AND INTESTINE.
299
rather suck the juices, of their casual or more
permanent victims.
Tne simple digestive tube of the Acari or
Mites is prolonged in a straight line from
mouth to anus. It is sometimes complicated
by gastric caeca or dilatations.
In the Aranei, or spiders proper, a~ slender
oesophagus passes back from the mouth to a
" stomach." Tiiis is sometimes a mere dila-
tation; sometimes is indicated by four sacculi,
that radiate from a narrow tube; and sometimes
presents a cavity, having blind prolongations
that extend into the bases of each of the
maxillary palpi and thoracic legs. All these
parts occupy the anterior Or cephalo-thoracic
division of the body. The remainder of the
canal, entering the abdominal segment, dilates,
after a single convolution, into a large and
sometimes globular intestine, to reach the
anus by a short portion, of narrower diameter,
called a rectum. The long tubes met with in the
Insects recur in this order. One set, of vary-
ing size, open in the neighbourhood of the
complicated apparatus of prehension ; these,
from their position, are supposed to be sali-
vary. And occasionally a special poison
gland appears to empty itself in this neigh-
bourhood. A middle set, called hepatic,
often forms two pairs of tubes, with orifices
much posterior to the gastric sacculi ; in other
cases they are very numerous, and are con-
cealed by a granular mass, which occupies the
same situation. The posterior set are one
or two pairs of long cseca, which join the
intestinal cavity close to its termination, and
are hence compared to urinary organs.
The Scorpions have a tolerably straight,
narrow, and simple tube, complicated by
several pairs of straight sacs, which come off
at right angles to its anterior part, and are
probably gastric crops. Below these, two
bifurcating tubes, of great length and small
diameter, open into a constriction of the
canal. They are regarded as hepatic.
In the order of MoUmgca, many of whom in-
habit the sea, we may again trace a gradual ad-
vance of development in the intestinal canal.
The Tumcata is its lowest subdivision.
Here a simple canal begins by a w r ide oeso-
phagus, that leads from the bottom of the
branchial sac to a stomach or dilatation. This
is surrounded by a number of hepatic follicles,
that open into its intestinal end ; and it leads
to a wide recurved intestine, which ends by an
aperture on the upper and outer surface of
the animal. Sometimes the liver varies from
this description in the fact that its follicles are
aggregated.
The Brachiopoda possess a digestive ap-
paratus of nearly equal simplicity with the
preceding. Dental structures are wanting ;
and the liver is still follicular.
The LameUibranch'uita exhibit a somewhat
similar condition. Their gastric cavity is
sometimes preceded by a short oesophagus.
From hence a comparatively simple intestine
continues, with a few convolutions, through a
mass of liver, to terminate, by a long straight
portion, in the anus. The latter segment, or
rectum, lies along the hinge of their shell, and
often perforates the heart in its course. Al-
though the liver is large and aggregate, it
opens by several ducts into the gastric dila-
tation.*
The Gasteropoda have a head, jaws, and
salivary follicles. Their longer oesophagus
sometimes dilates into an ingluvies or crop.
Their stomach often possesses a thickened
lining, and a masticatory apparatus of teeth or
plates, which make it a kind of gizzard.
Sometimes it is divided into two or more
compartments. The large liver opens into the
pyloric extremity of the stomach, or the com-
mencement of the intestine, by one or more
ducts; or, rarely, it empties itself into the
oesophagus. One or two large glandular caeca
also open into the beginning of the intestine,
and are regarded as a rudimentary pancreas.
The remainder of the tube is simple, and
ends anteriorly in the body, in accordance
with the general structure of the animal. In
the numerous herbivorous species, the intes-
tine is longer and more tortuous ; while the
crop, the gizzard, and the masticatory appa-
ratus all reach a high development.
The intestinal canal of the Pteropoda is very
similar. It possesses jaws and salivary glands,
together with an oesophagus, a crop, a gizzard,
a short and simple intestine, and a conglo-
merate liver that often opens by a single duct.
The Cephalopoda exhibit a marked advance
of development. Their mandibles form a
powerful organ of mastication ; and, in many
species, salivary glands co-exist. The mouth
leads to a long and dilatable oesophagus,
which descending, sometimes expands into a
crop before it finally reaches the gizzard or
muscular stomach. This organ is of tolerably
uniform appearance. Its shape is round,
or somewhat elongated ; it has a thick and
whitish epithelial lining, and its muscular
layer consists of two sets of fibres, each of
which radiates from a central tendon on one
side of the organ. The cardiac and pylo-
ric orifices are situated at its upper part.
The intestine coming from the latter soon
communicates with another cavity, which is
sometimes regarded as a stomach. This is,
in the lower Cephalopods, nearly spherical.
But in many of the higher or Dibranchiate
division, it is of less simple form, being
triangular, elongated, or folded spirally like a
snail shell. Its mucous membrane is rugous
and follicular ; and the large liver, which is
still supplied by arterial blood, opens into it
by a single duct. The intestine continues
hence as an uniform tube, which, after one or
two slight curves, bends upwards to open at
the base of the funnel. In some species we
also find caeca! appendages, the ducts of which
join those of the liver before they enter the
* In some species a curious style or hard conical
process occupies a tube of similar shape, that com-
municates with the gastric dilatatiou. The use of
this implement is unknown ; but it has been sug-
gested to effect a triturative process : a supposition
which, if true, would render the cavity containing
it the analogue of a gizzard.
300
STOMACH AND INTESTINE.
intestinal cavity. These have been supposed
to constitute a rudimentary pancreas.*
The alimentary canal of Fishes is simple,
wide, and short, compared with that of other
Vertebrata. Its chief subdivisions are an
(Esophagus, a stomach, and an intestine.
The oesophagus is large, dilatable, and mus-
cular. Its mucous membrane is generally
simple, sometimes involuted or glandular ;
and offers a remarkable contrast to the redder
and more vascular membrane of the stomach
at the point of their junction. As the dia-
meter of the tube rarely undergoes any great
and sudden increase in this situation the above
contrast of structure is often the only distinc-
tion between the two cavities.
The stomach varies greatly in size and
shape. Usually, however, it forms a curved
tube like a siphon. The obliteration of the
concave side of this tube converts it, by many
gradations in different genera, into the shape
of a two-necked flask, or of a blind tube with a
double orifice at one end. In other instances
it is dilated, or almost globular. Where tubu-
lar, it generally tapers away towards the pylo-
rus. And this end of the stomach, which is
usually more muscular than the cardiac, some-
times approaches the structure of a gizzard,
having constricted extremities, a thick muscu-
lar coat, and a scaly epithelium on its mucous
membrane. The valve itself is almost always
present, as a circular ridge of muscular fibre,
covered by a fold of mucous membrane.
The intestine of the fish is short and wide :
and generally consists of two portions, which
are separated from each other by a slight con-
striction into a small and large intestine. The
first receives the bile-duct, and the follicles
which form the rudimentary pancreas. The
latter also occasionally receives a caecal tube.
The intestine has the usual three coats
serous, muscular, and mucous. The serous
membrane is often pigmentary, and its cavity
communicates by apertures with the exterior.
It rarely forms a continuous mesentery ; the
attachment of the intestine being generally
ligamentous or filamentous, or even, as in
one instance f, by means of a mass of areolar
tissue that involves the whole tube. The
muscular coat is of unstriped fibres J, which
form two layers, the circular generally ex-
ternal.^ The mucous membrane is variously
folded : it sometimes contains ductless glands :
rarely it is ciliated. || The chief deviations from
these the ordinary characters of the intestine
* Many anatomists, however, consider the office
of this gland to be fulfilled by the cavity previously
mentioned. But strong arguments against this view
might be derived from the development of glands in
general, and of the pancreas in particular ; both in
the phases of individual life, and in the advance of