Chapter XVII: Part I: Morphology and Physiology (13)

FIG. 297.—Transverse section through an abdominal segment of larva of
_Megalopyge crispata_, showing the relations of the digestive canal
to the other organs: _int_, hind-intestine, with its mucous or
epithelial layer (_ep_), and _ml_ its outer or muscular layer; _ng_,
ventral ganglion; _ht_, heart; _mp_, urinary tubes; _f_, fat-body;
_sc_, thickened portion of the hypodermis (_hy_) containing the
setigenous cells; _m_, muscles; _m′_, a pair of retractor muscles
inserted near the base of the lateral glandular process (_lgp_);
_cut_, cuticula; _l_, legs. Also compare Figs. 142–144 and 234.
]

FIG. 298.
The alimentary or digestive canal of insects is a more or less
straight tube, which connects the mouth and anus, the latter
invariably
situated in the last segment of the body, under the last
tergite or suranal plate. It lies directly over the ventral nervous
cord and under the dorsal vessel, passing through the middle of the
body (Fig. 297). It is loosely held in place by delicate retractor
muscles (_retractores ventriculi_, found by Lyonet in the larvæ of
Lepidoptera, and occurring in those of Diptera), but is principally
supported by exceedingly numerous branches of the main tracheæ.
FIG. 298.—Internal anatomy of _Melanoplus femur-rubrum_: _at_, antenna
and nerve leading
to it from the “brain” or supraœsophageal ganglion (_sp_); _oc_,
ocelli, anterior and vertical ones,
with ocellar nerves leading to them from the brain; _œ_, œsophagus;
_m_, mouth; _lb_, labium or under
lip; _if_, infraœsophageal ganglion, sending three pairs of nerves to
the mandibles, maxillæ, and
labium respectively (not clearly shown in the engraving); _sm_,
sympathetic or vagus nerve, starting
from a ganglion resting above the œsophagus, and connecting with
another ganglion (_sg_) near the
hinder end of the crop; _sal_, salivary glands (the termination of the
salivary duct not clearly
shown by the engraver); _nv_, nervous cord and ganglia; _ov_, ovary;
_ur_, origin of urinary tubes;
ovt, oviduct; _sb_, sebaceous gland; _bc_, bursa copulatrix; _ovt_,
site of opening of the oviduct (the
left oviduct cut away); 1–10, abdominal segments. The other organs
labelled in full.—Drawn from
his original dissections by Mr. Edward Burgess.
]

FIG. 299.—Digestive canal of _Anabrus_: _m_, mouth: _œ_, œsophagus;
_sm_, the sympathetic nerve passing along the crop; _t_, tongue;
_fg_, frontal ganglion; _br_, brain, the nervous cord passing
backward from it; _sr_, salivary reservoir; _sg_, salivary gland;
_pv_, proventriculus; _ur_, origin of urinary tubes; _sb_, sebaceous
gland; 1–10, the ten abdominal segments.—Burgess _del._
]

It is in the higher adult insects differentiated into the mouth and _pharynx_, the _œsophagus_ or gullet, supplementary to which is the _crop_ (_ingluvies_) or “_sucking stomach_” of Lepidoptera, Diptera, and Hymenoptera; the _proventriculus_ or gizzard; the _ventriculus_, “chyle-stomach,” or, more properly, mid-intestine, and the hind-intestine, which is divided into the _ileum_, or short intestine, the long intestine, often slender and coiled, with the colon and the rectum. Morphologically, however, the digestive or enteric canal is divided into three primary divisions, which are indicated in the embryo insect; _i.e._, the _fore-intestine_ (_stomodæum_ of the embryo), _mid-intestine_ or “chyle-stomach,” and _hind-intestine_ or _proctodæum_ (Fig. 300). The three primary regions, with their differentiations, may be tabulated thus:—

_Fore-intestine_ (Stomodæum). Mouth and pharynx.
Pumping apparatus of Hemiptera,
Lepidoptera, and Diptera.
Œsophagus.
Crop or ingluvies, food reservoir, or
“sucking stomach.”
Proventriculus.

_Mid-intestine_ (Mesenteron). Mid-intestine, “chylific stomach,” or
ventriculus (with cœcal glands).

_Hind-intestine_ (Proctodæum). Ileum, or short intestine (with the
urinary tubes).
Long intestine.
Colon.
Rectum (with rectal glands).
Anus (with anal glands).

FIG. 300.—The three primary divisions of the alimentary canal of an
embryonic orthopterous insect: _br_, brain; _sbg_, subœsophageal
ganglion; _ng_, nervous cord; _st_, stomodæum; _pr_, proctodæum;
_mv_, malphigian tubes; _mesen_, mid-intestine; _ht_, heart; _md_,
mandibles; _mx_, _mx′_, 1st and 2d maxillæ.—After Ayers, with some
changes.
]

The appendages of the alimentary canal are: (1) the salivary and poison glands, which arise from the stomodæum in embryonic life; (2) while to the chylific stomach a single pair of cœcal appendages (Orthoptera and larval Diptera, _e.g._ Sciara), or many cœca may be appended; (3) the urinary tubes, also the rectal glands and the paired anal glands. In a Hemipter (_Pyrrhocoris apterus_) appendages arise from the intestine in front of the origin of the urinary tubes. In certain insects a single cœcal appendage (Nepa, Dyticus, Silpha, Necrophorus, and the Lepidoptera) arises from the proctodæum.

FIG. 301—Larva of honey-bee: _g_, brain; _bm_, ventral nervous cord;
_œ_, œsophagus; _sd_, spinning-gland; _cd_, mid-intestine or
chyle-stomach; _ed_, hind-intestine, not yet connected with the
mid-intestine; _vm_, urinary tube; _an_, anus; _st_, stigmata.—After
Leuckart, from Lang.
]

In certain larval insects, as those of the Proctotrypidæ (first larval stage), the higher Hymenoptera (ichneumons, ants, wasps, and bees, Fig. 301), in the Campodea-like larvæ of the Meloidæ and Stylopidæ, the larva of the ant-lion (Myrmecoleo), and those of _Diptera pupipara_ (Melophagus), the embryonic condition of the separation of the proctodæum and mid-gut (mesenteron) persists, the stomach ending in a blind sac; in such cases the intestine, together with the urinary tubes, is entirely secretory.

The anus is wanting in the larva of the ant-lion, as also in the wasps (in which there is a rudimentary colon) and in freshly hatched bees, though it becomes perfectly formed in the fully grown larvæ (Newport, art. Insecta, p. 967, and H. Müller).

In the larvæ of lamellicorn Coleoptera (_Melolontha vulgaris_) the digestive tube is nearly as simple as in bees, though there is a large colon, which at its beginning forms an immense cœcum, and has also one anal aperture (Newport).

The length and shape of the digestive canal is dependent on the nature of the food and also on the mode of life, especially the ease or difficulty with which the food is digested.

Newport, while stating that the length of the alimentary canal in
larvæ is not in general indicatory of the habits of the species,
makes this qualification after describing the digestive canal of
Calandra as compared with that of Calosoma: “The length and
complication of the intestines, therefore, appear to have some
reference to the quality of the food to be digested, since it is
well known that the food of these latter insects (weevils) is of
difficult assimilation, being as it is chiefly the hard ligneous
fibres of vegetable matter; but they cannot be received as always
indicatory of a carnivorous [or] vegetable feeder, since, as above
remarked, the length of the canal is considerable in one entirely
carnivorous larva, while it is much shorter in some herbivorous, and
particularly in pollenivorous larvæ, as in the Melolontha and the
apodal Hymenoptera.”

FIG. 302.—Digestive canal of a carabid beetle: _b_, œsophagus; _c_,
crop; _d_, proventriculus; _f_, mid-intestine, or “chyle-stomach,”
with its cœeca; _g_, posterior division of the stomach; _i_, the
two pairs of urinary tubes; _h_, intestine; _k_, rectum; _l_, anal
glands.—After Dufour, from Judeich and Nitsche.
]

Newport also contends that the length of the alimentary canal is not
more indicative in the perfect insect of the carnivorous or
phytophagous habits of the species than in the larva. It is nearly
as long (being from two to three times the length of the whole
body), and is more complicated, in the rapacious Carabidæ (Fig. 302)
than in the honey-sipping Lepidoptera, whose food is entirely
liquid. Referring to the digestive canal of Cicindelidæ, which is
scarcely longer than the body, he claims that “we cannot admit that
the length of the digestive organs, and the existence of a gizzard
and gastric vessels, are indicatory of predacity of habits in the
insect, because a similar conformation of parts exists often in
strictly vegetable feeders. The existence and length of these parts
seem rather to refer to the comparative digestibility of the food
than to its animal or vegetable nature.” Newport then refers to the
digestive canal of Forficulidæ (in which the gizzard is present, the
canal, however, passing in an almost direct line through the body,
making but one slight convolution), “a farther proof that the
_length_ of the canal must not be taken as a criterion whereby to
judge of the habits of a species.” He adds this will apply equally
well to the omnivorous Gryllidæ, in which there exists a short
alimentary canal, but a gizzard of more complicated structure than
that of the Dytiscidæ.

In larval insects and others (Synaptera, Orthoptera, etc.), in which the digestive canal is simplest, it is scarcely longer than the body, and passes through it as a straight tube.

In the caterpillar, which is a voracious and constant feeder, the digestive canal is a large straight tube, not clearly differentiated into fore-stomach, stomach, and intestine; but in the imago, which only takes a little liquid food, it is slender, delicate, and highly differentiated. In the larva the mid-gut forms the largest part of the canal; in the imago, the intestine becomes very long and coiled into numerous turns; at the same time the food-reservoir (the “sucking stomach”) develops, and the excretory tubes are longer.

_a._ The digestive canal

FIG. 303.—Interior view of the bottom of the head of _Danais
archippus_, the top having been cut away, showing, in the middle,
the pharyngeal sac with its five muscles: the frontal (_f.m_),
dorsal pair (_d.m_), and the lateral pair (_l.m_); _cl_, clypeus;
_cor_, cornea; _œ_, œsophagus; _p.m_, one of the large muscles which
move the labial palp.—After Burgess.
]

It will greatly simplify our conception of the anatomy of the digestive canal if we take into account its mode of origin in the embryo, bearing in mind the fact that during the gastrula condition the ectoderm is invaginated at each pole to form the primitive mouth and fore-gut (stomodæum) and hind-gut (proctodæum). The cells of the ectoderm secrete a chitinous lining (intima), which forms the continuation of the outer chitinous crust, and thus the lining of each end of the digestive canal is cast whenever the insect molts; while the mid-intestine (mesenteron), arising independently of the rest of the canal much later in embryonic life from the mesoderm, is not the result of any invagination, being directly derived from the mesoderm, and is not lined with chitin.

=The mouth, or oral cavity, and pharynx.=—This is the beginning of the alimentary bounded above by the clypeus, and labrum, with the epipharynx, and below by the hypopharynx, or tongue, as well as the labium. Into it pour the secretion of the salivary glands, which passes out through an opening at the base of the tongue or hypopharynx. On each side of the mouth are the mandibles and first maxillæ.

=The sucking or pharyngeal pump.=—This organ has been observed by Graber in flies and Hemiptera, but the fullest account is that by Burgess, who was the first to discover it in Lepidoptera. In the milk-weed butterfly (_Danais archippus_) the canal traversing the proboscis opens into a pharynx enclosed in a muscular sac (Figs. 303, 304, and 310).

The pharyngeal sac, says Burgess, serves as a pumping organ to suck the liquid food through the proboscis and to force it backwards into the digestive canal.

FIG. 304.—Longitudinal section through the head of Danais, showing the
interior of the left half: _mx_, left maxilla, whose canal leads
into the pharynx; _hph_, floor of the latter, showing some of the
taste-papillæ; _oe_, œsophagus; _ep_, epipharyngeal valve; _sd_,
salivary duct; _d.m_, _f.m_, and _cl_, as in Fig. 302.—After
Burgess.
]

Meinert (“Trophi Dipterorum”) has made elaborate dissections of the mouth and its armature, including the pharynx of several types of Diptera, with its musculature. He describes the pharynx as the principal, and in most Diptera, as the only part of the pump (antlia), and says: “By the muscles of the pump (_musculis antliæ_) the superior lamina of the pharynx is varied that the space between the two laminæ may be increased, and the liquid is thus led through the siphon formed by the mouth-parts into the mouth” (Fig. 81).

=The œsophagus.=—This is a simple tube, largest in those insects feeding on solid, usually vegetable, food, and smallest in those living on liquid food. It usually curves upwards and backwards, passing directly under the brain, and merges into the crop or proventriculus either at the back part of the head or in the thorax, its length being very variable. Its inner walls longitudinally are folded and lined with chitin.

According to Newport, in the œsophagus of the Gryllidæ, of the two layers of the mucous lining the second is distinctly glandular and secretory, and in it there are many thousands of very minute granular glandular bodies, which probably secrete the “molasses” or repellent fluid often ejected by these and other insects when captured.

=The crop or ingluvies.=—This, when present, is an enlargement of the end of the œsophagus, and lined internally with a muscular coat. It is very large in locusts (Fig. 298), Anabrus (Fig. 299), and other Orthoptera (the Phasmidæ excepted), in the Dermaptera, and most adult Coleoptera. A crop-like dilatation in front of a spherical gizzard is also present in the Synaptera (Poduridæ and Lepismidæ), as well as in the Mallophaga (Nirmidæ).

FIG. 305.—Digestive canal of Calandra: _H_, pear-shaped œsophagus;
_I_, crop; _K_, gastric cœca _L_, ilium; _MN_, colon; _P_, urinary
tubes.—After Newport.
]

FIG. 306.—Section of the crop (_H_), gizzard (_I_), and stomach (_K_)
of Athalia.-After Newport.
]

_Fig. 307._—Upper side of head and digestive canal of Myrmeleon larva:
_a_, crop; _b_, “stomach”; _c_, free ends of two urinary tubes;
_c′_, common origin of other six tubes; _d_, cœcum; _e_, spinneret;
_ff_, muscles for protruding its sheath; _gg_, maxillary
glands.—After Meinert, from Sharp.
]

In the larvæ of weevils (_Calandra sommeri_) there is a crop (Fig. 305), but not in the larva of Calosoma; also, according to Beauregard, in the pollen-eating beetles Zonitis, Sitaris, and Malabris it is wanting, while in Meloe it is highly developed (Kolbe).

The crop forms a lateral dilatation of the end of the œsophagus in the larvæ of weevils and of saw-flies (_Athalia centifoliæ_, Fig. 306).

=The “sucking stomach” or food-reservoir.=—This is a thin muscular pouch connected by a slender neck with the end of the œsophagus or the crop, when the latter is present. There is no such organ in Orthoptera, except in Gryllotalpa. It is wanting in the Odonata and in the Plectoptera (Ephemeridæ); in Platyptera (Perlidæ and Termitidæ), in Trichoptera, and in Mecoptera (Panorpidæ). In most adult Neuroptera (Myrmeleonidæ, Hemerobiidæ, and Sialidæ), but not in Rhaphidiidæ, the long œsophagus is dilated posteriorly into a kind of pouch or crop, and besides there is often a long “food-reservoir” arising on one of its sides, that of Myrmeleon (Fig. 307) and Hemerobius being on the right side.

FIG. 308.—Digestive canal of _Sarcophaga carnaria_: _a_, salivary
gland; _b_, œsophagus; _c_, food reservoir; _f-g_, stomach; _h_,
intestine; _i_, urinary tubes; _k_, rectum.—From Judeich and
Nitsche.
]

A true food-reservoir is present in most Diptera (Fig. 308) as well as in the larvæ of the Muscidæ, but according to Dufour it is wanting in some Asilidæ and in _Diptera pupipara_, and according to Brauer in the Œstridæ. The food-reservoir in Diptera is always situated on the left side of the digestive canal; there is usually a long neck or canal, while the reservoir is either oval or more usually bilobed, and often each lobe is itself curiously lobed.

In Lepidoptera (Figs. 309, 310) the so-called “sucking stomach” is, as Graber has proved, simply a reservoir for the temporary reception of food; though generally found to contain nothing but air, Newport has observed that in flies it is filled with food after feeding. He has found this to be the case in the flesh fly, and in Eristalis he has found it “partially filled with yellow pollen from the flowers of the ragwort upon which the insect was captured,” the pollen grains also occurring in the canal leading to the bag, in the gullet, and in the stomach itself. Graber has further proved by feeding flies with a colored sweet fluid that this sac is only a food-receptacle. As he says: “It can be seen filling itself fuller and fuller with the colored fluid, the sac gradually distending until it occupies half the hind-body.”

The food-reservoir of the Hymenoptera is a lateral pouch at the end of the long, slender œsophagus, and has been seen in the bee to be filled with honey.

FIG. 309.—Digestive canal of _Sphinx ligustri_: _h_, œsophagus; _i_,
rudiment of the gizzard; _k_, “stomach”; _q_, its pyloric end; _t_,
food reservoir; _p_, urinary tubes; _l_, ilium; _m_, cœcum of colon;
_n_, rectum; _v_, vent.—After Newport.
]

In the mole-cricket the hinder part of the crop is armed within with hook-like bristles directed backwards so as not to prevent the energetic pressure of the food backwards into the proventriculus, and to obviate the possibility of a regurgitation. (Eberli.)

=The fore-stomach or proventriculus.=—This is especially well developed in the Dermaptera, in the Orthopterous families Locustidæ, Gryllidæ, and Mantidæ, while in the Thysanura (Lepisma) there is a spherical gizzard provided with six teeth. It also occurs in many wood-boring insects, and in most carnivorous insects, notably the Carabidæ, Dyticidæ, Scolytidæ, in the Mecoptera (scorpion-flies), in the fleas, and in many kinds of ants, as well as Cynips, Leucospis, and Xyphidria. It is very muscular, lined within with chitin, which is usually provided with numerous teeth arising from the folds. These folds begin in the œsophagus or crop, and suddenly end where the mesenteron (“chylific stomach”) begins. It has been compared with the gizzard of birds, and is usually called by German authors the chewing or masticating stomach. (Kaumagen.)

The proventriculus is best developed in the Gryllidæ (_Acrida
viridissima_), where the six folds at the end of the crop close
together to form a valve between the crop and proventriculus. “They
are each armed with five very minute hooked teeth; and, continued
into the gizzard, develop many more in their course through that
organ. These first teeth are arranged around the entrance to the
gizzard, and seem designed to retain the insufficiently comminuted
food and to pass it on to that organ.

FIG. 310.—Anatomy of _Danais archippus_ after removal of right half
of the body. _Lettering of the head_: _a_, antenna; _ph_, pharynx;
_pl_, labial palpi; _r_, proboscis; _g_, brain; _usg_,
subœsophageal ganglion. _Lettering of the thorax_: I. II. III.
thoracic segments; _b_{1}_, _b_{2}_, _b_{3}_, the coxal joints of
the three pairs of legs; _bm_, muscles of the wings; _ac_ cephalic
aorta with its swelling; _œ_, œsophagus; _bg_, thoracic ganglia of
the ventral cord; _sd_, salivary glands of one side, those of the
other side cut off near their entrance into the common salivary
duct. _Lettering of the abdomen_: 1–9. abdominal segments; _h_,
heart; _sm_, so-called sucking-stomach (food-reservoir); _cm_,
chyle-stomach; _ag_, abdominal ganglia: _ed_, hind intestine with
colon (_c_) and rectum (_r_); _rm_, urinary vessels; _ov_, ovarial
tubes, those of the right side cut off; _ove_, terminal filaments
of the ovaries; _bc_, bursa copulatrix; _obc_, its outer aperture;
_od_, oviduct; _vag_, vagina; _wo_, its outer aperture; _ad_,
glandular appendages of the vagina partly cut away; _vk_,
connective canal between the vagina and bursa copulatrix with
swelling (receptaculum seminis); _an_, anus.—After Burgess, from
Lang.
]

FIG. 311.—Transverse section of the proventriculus of _Gryllus
cinereus_: _muc_, muscular walls; _r_, horny ridge between the
large teeth (_sp_).—After Minot.
]

FIG. 312.—Transverse section of the proventriculus of the
cockroach.—After Miall and Denny.
]

FIG. 313.—Digestive canal of the honey-bee: _A_, horizontal section
of the body; _lp_, labial palpus; _mx_, maxilla; _e_, eye; _pro.
t_, prothorax; _mesa. t_, mesothorax; _meta. t_, metathorax; _dv_,
dorsal vessel; _v_, _v_, ventricles of the same; No. 1, No. 2, No.
3, salivary gland systems; _œ_ œsophagus; _g_, _g_, ganglia of
chief nerve-chain; _n_, nerves; _hs_, honey-sac; _p_, petaloid
stopper or calyx of honey-sac or stomach-mouth; _c. s_, chyle
stomach; _bt_, urinary tubes; _si_, small intestine (ilium); _l_,
“lamellæ or gland-plates of colon,” rectal glands; _li_, rectum.
_B_, cellular layer of stomach; _gc_, gastric cells, × 200. _C_,
urinary tube; _bc_, cells; _t_, trachea. _D_, inner layer, with
gastric teeth (_gt_).—After Cheshire.
]

“Next to these in succession on each of the longitudinal ridges are
four flat, broad, somewhat quadrate teeth, each of which is very
finely denticulated along its free margin. These extend about
half-way through the gizzard. They appear to be alternately elevated
and depressed during the action of the gizzard, and to serve to
carry on the food to the twelve cutting teeth, with which each ridge
is also armed, and which occupy the posterior part of the organ.
These teeth are triangular, sharp-pointed, and directed posteriorly,
and gradually decrease in size in succession from before backward.
Each tooth is very strong, sharp-pointed, and of the color and
consistence of tortoise shell, and is armed on each side by a
smaller pointed tooth. These form the six longitudinal ridges of the
gizzard, between each two of which there are two other rows of very
minute teeth of a triangular form, somewhat resembling the larger
one in structure, occupying the channels between the ridges. The
muscular portion of the gizzard is equally interesting. It is not
merely formed of transverse and longitudinal fibres, but sends from
its inner surface into the cavity of each of the large teeth other
minute but powerful muscles, a pair of which are inserted into each
tooth. The number of teeth in the gizzard amounts to 270, which is
the same number in these Gryllidæ as found formerly by Dr. Kidd in
the mole-cricket. Of the different kinds of teeth there are as
follows: 72 large treble teeth, 24 flat quadrate teeth, 30 small
single-hooked teeth, and 12 rows of small triangular teeth, each row
being formed of 12 teeth. This is the complicated gizzard of the
higher Orthoptera.” (Newport.)

In the more generalized cockroach, there are six principal folds,
the so-called teeth, which project so far inwards as to nearly meet
(Fig. 312). The entire apparatus of muscles and teeth is, as Miall
and Denny state, “an elaborate machine for squeezing and straining
the food, and recalls the gastric mill and pyloric strainer of the
crayfish. The powerful annular muscles approximate the teeth and
folds, closing the passage, while small longitudinal muscles, which
can be traced from the chitinous teeth to the cushions, appear to
retract these last, and open a passage for the food.”

As in the fore-stomach or proventriculus of the lobster, the solid, rounded teeth do not appear to triturate the solid fragments found in the organ, but act rather as a pyloric strainer to keep such bodies out of the chylific stomach. We accept the view of Plateau that this section of the digestive canal in insects, which he compares to the psalterium of a ruminant, is a strainer rather than a masticatory stomach, and both Forel and Emery, as well as Cheshire, take this view.

The proventriculus of the honey-bee (Fig. 313, _hs_) is called by apiarians the “honey-sac” or “honey-stomach.” Cheshire states that if it be carefully removed from a freshly killed bee, its calyx-like “stomach-mouth” may be seen to gape open and shut with a rapid snapping movement. The entrance to the stomach is guarded by four valves, each of which is strongly chitinous within, and fringed along its edge with downward-pointing fine stiff bristles. By the contraction of the longitudinal muscles (_lm_), the valves open to allow the passage of food from the honey-sac to the “chyle-stomach.” It is closed at will by circular muscles (_tm_). Then the bee can carry food for a week’s necessities, either using it rapidly in the production of wax, or eking it out if the weather is unfavorable for the gathering of a new store.

FIG. 314.—“Honey-sac stopper,” “stomach-mouth,” or calyx-bell of
honey-bee, × 50. _A_, front view of one of the lobes of the
calyx-bell; _l_, lip-like point, covered by down-turned bristles
(_b_); _sm_, side membrane. _B_, longitudinal section of the
stomach-mouth, with continuations into entrance of chyle-stomach;
_l_, _l_, lip-like ends of leaflets; _s_, setæ; _lm_, longitudinal
muscles; _tm_, transverse muscles in cross-section; _cl_, cell-layer
of honey-sac; _LM_, _TM_, longitudinal and transverse muscles of
same; _nc_, nucleated cells of tubular extension of stomach-mouth
into chyle-stomach; _lm′_, _tm′_, longitudinal and transverse
muscles of chyle stomach; _c_, _c_, cells covered within by an
intima. _C_, cross-section of stomach-mouth; _m_, cross-section of
muscles seen at _lm_ in _B_; _tm_, transverse muscles surrounding
stomach-mouth. _D_, cross-section through small intestine; _a_ and
_m_, longitudinal and surrounding muscles.—After Cheshire.
]

Cheshire also shows that when bees suck up from composite and other
flowers nectar together with much pollen, the outside wrinkled
membrane (_sm_, _A_, Fig. 314) “is seen to continually run up in
folds, and gather itself over the top of the stomach-mouth, bringing
with it, by the aid of its setæ, the large pollen-grains the nectar
contains.” The lips (_l_, _l_, _B_, Fig. 314), now opening, take in
this pollen, which is driven forwards into the cavity made between
the separating lips by an inflow of the fluid surrounding the
granules. The lips in turn close, but the down-pointing bristles are
thrown outwards from the face of the leaflet, in this way revealing
their special function, as the pollen is prevented from receding
while the nectar passes back into the honey-sac, strained through
between the bristles aforesaid, the last parts escaping by the
loop-like openings seen in the corners of _C_, Fig. 314. The whole
process is immediately and very rapidly repeated, so that the pollen
collects and the honey is cleared. “Three purposes, in addition to
those previously enumerated, are thus subserved by this wondrous
mechanism. First, the bee can either _eat or drink_ from the mixed
diet she carries, gulping down the pollen in pellets, or swallowing
the nectar as her necessities demand. Second, when the collected
pollen is driven forwards into the chyle-stomach, the tube
extension, whose necessity now becomes apparent, prevents the
pellets forming into plug-like masses just below _p_, Fig. 313, for,
by the action of the tube, these pellets are delivered into the
midst of the fluids of the stomach, to be at once broken up and
subjected to the digestive process. And third, while the little
gatherer is flying from flower to flower, her stomach-mouth is busy
in separating pollen from nectar, so that the latter may be less
liable to fermentation and better suited to winter consumption. She,
in fact, carries with her, and at once puts into operation, the most
ancient, and yet the most perfect and beautiful, of all
‘honey-strainers.’”

Forel’s experiments on the proventriculus of ants prove that through
its valvular contrivance it closes the passage from the crop to the
mid-intestine (“chylific stomach”), and allows the contents of the
former to pass slowly and very gradually into the latter. Emery
confirms this view, and concludes that the organ in the Camponotidæ
and in the Dolichoderidæ provided with a calyx-bell, usually
regarded as a triturating stomach (Kaumagen), but more correctly as
a pumping stomach, consists of parts which perform two different
functions. Under the operation of the muscles of the crop the
entrance to the pumping stomach becomes closed, in order by such
spasmodic contraction to prevent the flow of the contents of the
crop into the proventriculus. By the pressure of the transverse
muscles of the proventriculus its contents are emptied into the
mid-intestine, while simultaneously a regurgitation into the crop is
prevented. In the Dolichoderidæ and Plagiolepidinæ the closure in
both cases is effected by the valves. In the true Camponotidæ there
are two separate contrivances for closing; the calyx belonging to
the crop-musculature, while the valves essentially belong to the
proventricular pumping apparatus.

Opinions vary as to the use of this portion of the digestive canal.
Graber compares it to the gizzard of birds, and likens the action of
the rosette of teeth to the finer radiating teeth of the sea-urchin,
and styles it a chopping machine, which works automatically, and
allows no solid bits of food to pass in to injure the delicate walls
of the stomach (mid-gut).

He also states that the food when taken from the proventriculus is
very finely divided, while that found in the œsophagus contains
large bits.

Kolbe says that this view has recently been completely abandoned,
and that the teeth are used to pass the food backwards into the
chylific stomach. “But Goldfuss had denied the triturating action of
the proventriculus of the Orthoptera (Symbolæ ad Orthopterorum
quorundam Œconomiam, 1843), stating that the contents of the same
are already fluid in the gullet, so that the fore-stomach (Kaumagen)
does not need to comminute the food” (Kolbe). In the Gryllidæ and
Locustidæ, just before the posterior opening of the proventriculus
into the stomach the chitinous lining swells into a ring and
projects straight back as the inner wall of the cylindrical chylific
stomach. The muscular layer forms two sac-like outgrowths or folds,
which separate on the circular fold from the chitinous membrane.
This apparatus only allows very finely comminuted food to pass into
the stomach.

In the Acrydiidæ (_Eremobia muricata_) at the end of the
proventriculus, where it passes into the stomach, is a small
circular fold which hangs down like a curtain in the stomach.

=The œsophageal valve.=—Weismann[50] states that the origin of the proventriculus in the embryo of flies (Muscidæ) shows that it should be regarded as an intussusception of the œsophagus. While in the embryo the invaginated portion of the œsophagus is short, after the hatching of the larva it projects backwards into the mid-intestine. Kowalevsky also observed in a young muscid larva, 2.2 mm. in length, that the œsophagus, shaped like a tube, extends back into the expanded portion (proventriculus) and opens into the stomach (Fig. 315, _A_). In a larva 10 mm. long the funnel is shorter, the end being situated in the proventriculus (Fig. 315, _B_, _pr_). In the cavity between the outer (_o_) and inner wall (_i_) no food enters, and the use of this whole apparatus seems to be to prevent the larger bits of food from passing into the chylific stomach (Kowalevsky).

FIG. 315.—Œsophageal valve of young muscid larva: _m_, its opening:
_t_, thickening of the cells; _mes_, mesoderm.—After Kowalevsky.
]

Beauregard has found a similar structure in the Meloidæ, and calls
it the “cardiac valvule” (Fig. 318, _Kl_). It was observed by
Mingazzini in the larvæ of phytophagic lamellicorn beetles, and
Balbiani described it in a myriopod (Cryptops) under the name of the
“œsophageal valvule.”

Gehuchten describes a homologous but more complicated structure in a
tipulid larva (_Ptychoptera contaminata_), but differing in
containing blood-cavities, as a tubular prolongation of the
posterior end of the œsophagus which passes through the
proventriculus and opens at various positions in the anterior part
of the chylific stomach (Fig. 316).

The three layers composing this funnel are distant from each other
and separated by blood-cavities, the whole forming “an immense
blood-cavity extended between the epithelial proventricular lining
and the muscular coat.”

According to Schneider the longitudinal muscular fibres of the fore
and hind gut in insects pass into the stomach (mid-gut). The
anterior part of the fore-gut has generally only circular fibres.
When, however, the longitudinal fibres arise behind the middle, then
they separate from the digestive canal and are inserted a little
behind the beginning of the chylific stomach. Hence there is formed
an invagination of the proventriculus, which projects into the
cavity of the stomach.

Schneider describes this process, which he calls the “beak,” as an
invagination of the fore-stomach which projects into the cavity of
the stomach. The two layers of the invagination in growing together
form a beak varying in shape, being either simple or lobed and armed
with bristles or teeth. This beak is tolerably large in Lepisma,
Dermaptera (Forficula), Orthoptera, and in the larvæ and adults of
Diptera, but smaller in the Neuroptera and Coleoptera, while in
other insects it is wanting.

=Proventricular valvule.=—Gehuchten also describes in Ptychoptera
what he calls “the proventricular valvule,” stating that it is “a
circular fold of the intestinal wall” (Fig. 310, _vpr_). He claims
that it has not before been found, the “proventricular beak” of
Schneider being regarded by him as the œsophageal valvule.

FIG. 316.—Digestive canal of _Ptychoptera contaminata_: _gs_, salivary
glands; _ra_, œsophagus; _pr_, proventriculus; _gt_, crown of eight
small tubular glands; _im_, mid-intestine; _ga_, two accessory white
glands; _vm_, urinary vessels; _ig_, small intestine; _gi_, large
intestine; _r_, rectum; _A_, the proventriculus in which the hinder
end of the œsophagus extends as far as the chyle-stomach. _B_,
longitudinal section of the proventricular region; _sph_, muscular
ring or œsophageal sphincter; _ppr_, wall of the proventriculus;
_e_, circular constriction dividing the cavity of the proventriculus
in two; _vpr_, circular fold of the wall of the mid-intestine
forming the proventricular valve; _vœ_, œsophageal valve.—After
Gehuchten.
]

=The peritrophic membrane.=—This membrane appears first to have been noticed by Ramdohr in 1811 in _Hemerobius perla_. It has been found by Schneider, who calls it the “funnel.” On the hinder end of the fore-stomach, he says, the cuticula forms a fold enclosing the outlet of the fore-stomach, and extending back like a tube to the anus. This “funnel,” he adds, occurs in a great number of insects. It has been found in Thysanura, but is wanting in Hemiptera. In the Coleoptera it is absent in Carabidæ and Dyticidæ. It is generally present in Diptera and in the larvæ of Lepidoptera, but not in the adults. In Hymenoptera it has been found in ants and wasps, but is absent in Cynipidæ, Ichneumonidæ, and Tenthredinidæ. All those insects (including their larvæ) possessing this funnel eat solid, indigestible food, while those which do not possess it take fluid nourishment. It is elastic, and firmly encloses the contents of the digestive tract. Until Schneider’s discovery of its general occurrence, it had only been known to exist in the viviparous Cecidomyia larvæ (Miastor). Wagner, its discoverer, noticed in the stomach of this insect a second tube which contained food. Pagenstecher was inclined to regard the tube as a secretion of the salivary glands. Metschnikoff, however, more correctly stated that the tube consisted of chitin, but he regarded it as adapted for the removal of the secretions. (Schneider.) Plateau, however, as well as Balbiani, the latter calling it the “peritropic membrane,” considers this membrane as a secretion of the chylific stomach, and that it is formed at the surface of the epithelial cells. It surrounds the food along the entire digestive tract, forming an envelope around the fæcal masses. On the other hand, Gehuchten states that in the larva of Ptychoptera its mode of origin differs from that described by Plateau and by Schneider, and that it is a product of secretion of special cells in the proventriculus.

=The mid-intestine.=—This section of the digestive canal, often, though erroneously, called the “chylific stomach” or ventriculus, differs not only in its embryonic history, but also in its structure and physiology from the fore and hind intestine of arthropods, and also presents no analogy to the stomach of the vertebrate animals. In insects it is a simple tube, not usually lined with chitin, since it is not formed by the invagination of the ectoderm, as are the fore and hind intestine, the absence of the chitinous intima promoting the absorption of soluble food. Into the anterior end either open two or more large cœcal tubes (Fig. 299), or its whole outer surface is beset with very numerous fine glandular filaments like villi (Fig. 317 and Fig. 329).

The mid-intestine varies much in size and shape; it is very long in the lamellicorn beetles (Melolontha and Geotrupes), and while in Meloë it is very large, occupying the greatest part of the body-cavity, in the longicorn beetles and in Lepidoptera it is very small. The pyloric end consists of an internal circular fold projecting into the cavity. In the Psocidæ (Cæcilius) the pyloric end is prolonged into a slender tube nearly as long as the larger anterior portion.

The limits between the mid and hind intestine are in some insects difficult to define, the urinary tubes sometimes appearing to open into the end of the mid-intestine (“stomach”). The latter also is sometimes lined with an intima. The limits are also determined by a circular projection, directly behind which is an enlargement of the intestine in the shape of a trench (_rigole_), or circular _cul-de-sac_ (the “pyloric valvule” of some authors, including Beauregard), while the walls of the small intestine contract so as to produce a considerable constriction of the cavity of the canal. This constriction exactly coincides with the beginning of the double layer of circular muscles in the wall of the small intestine. An internal layer, which is the continuation of the circular muscles of the chylific stomach, and an external layer much more developed probably belong to this part of the alimentary canal. Since the homologue of the circular fold occurs in the locust as well as in Diptera, it is probably common to insects in general.

FIG. 317.—Digestive canal of _Carabus monilis_: _h_, œsophagus; _i_,
gizzard or proventriculus; _k_, “stomach,” with its cœca (_r_); _p_,
urinary tubes; _q_, their point of insertion; _m_, _n_, colon, with
cœcal glands; _s_, anal glands; _a_, _b_, _c_, a gastric cœcum; _a_,
_b_, portion of lining of gizzard.—After Newport.
]

FIG. 318.—Digestive canal of Meloe: _sch_, œsophagus; _Kl_, œsophageal
valve; _mD_, mid-intestine; _eD_, hind-intestine; _Ei_, eggs; _g_,
sexual opening.—After Graber.
]

Gehuchten adds that the limit set by the circular projection does
not exactly coincide with the opening into the intestine of the
urinary tubes and the two annexed glands. He shows by a section (his
Fig. 133) that the tubular glands open into the alimentary canal in
front of the circular fold. It is the same with the Malpighian
tubes. They are not, therefore, he claims, dependences of the
terminal intestine, but of the mid-intestine. Beauregard has
observed the same thing in the vesicating insects (Meloidæ). The
Malpighian tubes, he says, open into the “chylific stomach” before
the valvular crown. This arrangement does not seem to be general,
because, according to Balbiani, the Malpighian vessels open into the
beginning of the intestine in Cryptops. Compare also Minot’s account
of the valve in locusts separating the stomach from the intestine,
and in front of which the urinary or Malpighian tubes open.

=Histology of the mid-intestine.=—The walls of the stomach are composed of an internal epithelium, a layer of connective tissue, with two muscular layers, the inner of which is formed of unstriated circular muscular fibres, and the outer of striated longitudinal muscular fibres.

In the cockroach short processes are given off from the free ends of the epithelial cells, as in the intestine of many mammals and other animals. “Between the cells a reticulum is often to be seen, especially where the cells have burst; it extends between and among all the elements of the mucous lining, and probably serves, like the very similar structure met with in mammalian intestines, to absorb and conduct some of the products of digestion.” (Miall and Denny.)

Gehuchten shows that the epithelial lining of the mesenteron (chylific stomach) of the dipterous larva Ptychoptera is composed of two kinds of cells, _i.e._ secreting or glandular cells and absorbent cells, the former situated at each end of the stomach, and the absorbent cells occupying the middle region. The part played by these cells in digestion will be treated of beyond in the section on digestion. (See p. 327.)

=The hind-intestine.=—In many insects this is divided into the ileum, or short intestine, and the long intestine. The limit between the intestine and stomach is externally determined by the origin of the urinary tubes, which are outgrowths of the anterior end of the proctodæum. Like the fore-intestine the hind-intestine is lined with a thick muscular layer, and, as Gehuchten states, the passage from the epithelial lining of the stomach (mid-intestine) to the muscular lining of the intestine is abrupt.

=Large intestine.=—In Ptychoptera, as described by Gehuchten, there are no precise limits between the small and large intestine; the epithelium of the large intestine has a special character, and its constituents present a close resemblance to the absorbed cells of the chylific stomach, being like them large and polygonal. The muscular layer is not continuous, and is formed of longitudinal and circular fibres, the latter being the larger.

=The ileum=—Though in most insects slender, and therefore called the small intestine, the ileum is in locusts (Fig. 298) and grasshoppers (Anabrus, Fig. 299) as thick as the stomach. In many carnivorous beetles (Dyticus, Fig. 320, _il_, and Necrophorus) it is very long, but rather slender and short in the Carabidæ and Cicindelidæ, as well as those insects whose food is liquid, such as Diptera. In the Lepidoptera it varies in length, being in Sphinx quite long and bent into seven folds (Fig. 309), while it is very short in the Psocidæ, Chrysomelidæ, and Tenthredinidæ.

In the locust the ileum is traversed by six longitudinal folds with intervening furrows; outside of each furrow is a longitudinal muscular band. Seen from the inner surface the epithelium has an unusual character, the cells in the middle of each of the flat folds being quite large, polygonal in outline, while towards the furrows the cells become very much smaller. The walls are double when seen in transverse section, the inner layer consisting of epithelial cells resting on connective tissue, the outer layer formed of circular muscles. The cuticula is thin, but probably chitinous; it resembles that on the gastro-ileal folds, except that there are no spinules, but unlike the cuticula of the stomach it extends equally over the folds and the furrows. (Minot.) In the cockroach the junction of the small intestine with the colon is abrupt, a well-developed annular fold assuming the nature of a circular valve. (Miall and Denny.)

=The gastro-ileal folds.=—In the locust the intestine is separated from the chylific stomach by what Minot calls “the gastro-ileal folds,” which form a peculiar valve. The urinary vessels open just underneath and in front of this valve. In Melanoplus, and probably in the entire family of Acrydiidæ, they are indicated as “dark spots, round in front and lying at the anterior end of the ileum so as to form a ring around the interior of the intestine.” They are 12 in number, and all alike. They are pigmented and round in front where they are broadest and stand up highest; they narrow down backwards, the pigment disappears, and they gradually fade out into the ileal folds. Directly beneath them, and just at the posterior end of the stomach, there is a strong band of circular striated muscular fibres. The epithelium of these folds is covered with minute conical spines, which are generally, but not always, wanting between the folds. (Minot.)

=The colon.=—This section of the intestine (Fig. 319) is sometimes regarded as a part of the rectum. In the locust the six longitudinal folds of the ileum are continued into the colon, but their surface, instead of being smooth as in the ileum, is thrown up into numerous irregular curved and zigzag secondary folds. The cells of the epithelium are of uniform size, and the layer is covered by a highly refringent cuticula without spines; and, like that in the ileum, it rests on a layer of connective tissue, beyond which follows (1) an internal coat of longitudinal, and (2) an external coat of circular striated muscular fibres. (Minot.)

FIG. 319.—Digestive canal of _Lucanus cervus_: _G_, anterior muscles
of the pharynx; _H_, œsophagus; _I_, gizzard; _K_, chyle-stomach;
_L_, ilium; _M_, colon (cœcal part of); _N_, colon; _O_, rectum;
_a_, frontal ganglion of the vagus; _b_, vagus nerve; _c_, anterior
lateral ganglion connected with the vagus.—After Newport.
]

In butterflies (_Pontia brassicæ_), in _Sphinx ligustri_, and probably in most Lepidoptera the colon is distinct from the rectum, and is anteriorly developed into a very large more or less pyriform or bladder-like cæcum (Figs. 309, 310), which in certain Coleoptera (Dyticus, Fig. 320, _d_; Silpha, Necrophorus, etc.) is of remarkable length and shape; it also occurs in Nepidæ (Fig. 327). In the cockroach a lateral cæcum “is occasionally, but not constantly, present towards its rectal end,” and a constriction divides the colon from the rectum. (Miall and Denny.)

=The rectum.=—The terminal section of the hind-gut varies in length and size, but is usually larger than the colon, and with thick, muscular walls. In Lepidoptera it is narrow and short.

The rectum is remarkable for containing structures called rectal glands (Fig. 298). Chun describes those of _Locusta viridissima_ as six flat folds, formed by a high columnar epithelium and a distinct cuticula; there is a coat of circular bands corresponding to the furrows between the glands. Minot states that this description is applicable to the locusts (Acrydiidæ) he has investigated, the only difference being in the structural details of the single layers. He claims that the rectal folds “do not offer the least appearance of glandular structure,” neither is their function an absorbent one, as Chun supposed. From their structure and position Fernald regards the rectal glands of Passalus as acting like a valve, serving to retain the food in the absorptive portions of the digestive tract till all nutriment is extracted.

FIG. 320.—_Dyticus marginalis_, ♂ opened from the back: _a_, crop;
_b_, proventriculus; _c_, mid-intestine beset with fine cœcal
glands; _d_, long cœcal appendage of the colon; apodemes;
_B_{1}_-_B_{3}_, apodemes; _vhm_, coxal extensor muscle, moving the
hind leg; _ho_, testis; _dr_, accessory gland; _r_, penis; _e_,
reservoir of the secretion of the anal gland.—After Graber.
]

The epithelial folds of the larvæ of dragon-flies serve as organs of respiration, the water being admitted into this cavity, and when forcibly expelled serving to propel the creature forward. Paired and single anal glands (repugnatorial) enter the rectum of certain Coleoptera (Figs. 302, _l_; 317, _s_; 320, _e_).

=The vent (anus).=—The external opening of the rectum is situated in the end of the body, in the vestigial 10th or 11th abdominal segment, and is more or less eversible. It is protected above in caterpillars, and other insects with 10 free abdominal segments, by the suranal plate. It is bounded on the sides by the paranal lobes, while beneath is the infra-anal lobe.

The anus is wanting in certain insects, and where this is the case the hind-gut, owing to a retention of the embryonic condition, is usually separated from the mid-intestine. (See p. 300.)

FIG. 321.—Enteric canal of _Psyllopsis fraxinicola_: _œ_, œsophagus;
_md_, mid-intestine; _ed_, hind-intestine; _vm_, urinary vessels;
_s_, the coil formed by the hind-intestine and the most anterior
part of the mid-intestine.—After Witlaczil, from Lang.
]

Some remarkable features of the digestive canal in hemipterous
insects are noteworthy. In the Coccidæ, according to Mark, the
anterior end of the long mid-intestine forms, with the hinder end of
the œsophagus, a small loop, whose posterior end is firmly grown to
the wall of the rectum, and forms a cup-like invagination of the
latter. Then the rest of the tube-like stomach turns sidewise and
forms a large loop, which turns back on itself and occupies a large
part of the body-cavity. This loop receives on the anterior end,
near the œsophagus, the two urinary vessels, and forms just below
the opening into the rectum a short cæcum.

In other homopterous genera (Psyllidæ and some Cicadidæ) Witlaczil
describes nearly the same peculiarity, the mid-gut and part of the
intestine forming a loop growing together for a certain distance and
winding round each other (Fig. 321).

=Histology of the digestive canal.=—In all the divisions of the digestive canal of insects the succession of the cellular layers composing it is the same: 1st, a cuticula; 2d, an epithelium; 3d, connective tissue; 4th, muscular tissue. In the locust, the first division of the canal (fore-gut), there are two muscular coats, an internal longitudinal and an external circular coat; the fibres are all striated. The lining epithelium is not much developed, but forms a thick, hard, and refringent cuticula, which is thrown up into spiny ridges. In the second division (mid-gut, “stomach”) the epithelium is composed of very high columnar cells, which make up the greater part of the thickness of the walls, while the cuticula is very delicate, slightly refringent, with no ridges, and is probably not chitinous; the fibres of the muscular coats are not striated, while this division is also distinguished by the presence of glandular follicles and folds. The stomach and the cæcal appendages have all these peculiarities in common, while no other part of the canal is thus characterized.

The third division (intestine and rectum) is composed of an epithelium, the cells of which are intermediate in size between those of the fore and mid gut. The cells are often pigmented, and they are covered by a much thicker cuticula than that of the stomach, but which is not so thick and hard as that of the œsophagus and proventriculus. The very refringent cuticula is not thrown up into ridges, though in some parts it is covered with delicate conical spines, which are very short. “The epithelium and underlying connective tissue (_tunica propria_) are thrown up into six folds, which run longitudinally, being regular in the ileum and rectum (as the rectal glands), but very irregular in the colon. Outside the depression between each two neighboring folds there is a longitudinal muscular band, these making six bands. This peculiar disposition of the longitudinal muscles does not occur in any other part of the canal; it is, therefore, especially characteristic of the third division.” (Minot.)

LITERATURE ON THE ORGANS OF DIGESTION

=Treviranus, G. R.= Resultate einiger Untersuchungen über den inneren
Bau der Insekten. (Verdauungsorgane von _Cimex rufipes_.) (Annal. d.
Wetterau. Gesells., 1809, i, pp. 169–177, 1 Taf.)

=Ramdohr, C. A.= Abhandlungen über die Verdauungswerkzeuge der
Insekten. 1811, vii, pp. 221, 30 Taf.

=Dutrochet, R. J. H.= Mémoire sur les métamorphoses du canal
alimentaire dans les insectes. (Journal de Physique, 1818, lxxxvi,
pp. 130–135, 189–204; Meckel’s Archiv, 1818, iv, pp. 285–293.)

=Suckow, F. W. L.= Verdauungsorgane der Insekten. (Heusinger’s
Zeitschr. f. organ. Physik., 1828, iii, pp. 1–89.)

=Doyère, L.= Note sur le tube digestif des Cigales. (Ann. Sc. nat.
Zool., 1839, 2 Sér., xi, pp. 81–85.)

=Grube, A. E.= Fehlt den Wespen- oder Hornissenlarven ein After oder
nicht? 1 Taf. (Müller’s Archiv für Physiol., 1849, pp. 47–74.)

=Sirodot.= Recherches sur les sécrétions chez les insectes. (Ann. Sc.
nat. Zool., 1858, 4 Sér., x, pp. 141–189, 251–328, 12 Pls.)

=Milne-Edwards, H.= Leçons sur la physiologie et l’anatomie comparée,
v, 1859, pp. 498–536, 581–638.

=Dufour, L.= Recherches anatomiques sur les Carabiques et sur
plusieurs autres insectes Coléoptères. Appareil digestif. (Ann. Sc.
nat., ii, 1824, pp. 462–482, 2 Pls.; iii, 1824, pp. 215–242, 5 Pls.,
pp. 476–491, 3 Pls.; iv, 1824, pp. 103–125, 4 Pls.; iv, 1825, pp.
265–283.)

—— Recherches anatomiques sur l’Hippobosque des chevaux. (Ann. Sc.
nat., 1825, vi, pp. 299–322, 1 Pl.)

—— Description et figure de l’appareil digestif de l’_Anobium
striatum_. (Ibid., xiv, 1828, pp. 219–222, 1 Pl.)

—— Recherches anatomiques sur les Labidoures. Appareil de la
digestion. (Ibid., xiii, 1828, pp. 348–354, 2 Pls.)

—— Recherches anatomiques et considerations entomologiques sur
quelques insectes Coléoptères, compris dans les familles des
Dermestins, des Byrrhiens, des Acanthopodes et des Leptodactyles.
Appareil digestif. (Ibid., Sér. 2, Zool., i, 1834, pp. 67–76, 2
Pls.)

—— Résumé des recherches anatomiques et physiologiques sur les
Hémiptères. (Ibid., pp. 232–239.)

—— Mémoire sur les métamorphoses et l’anatomie de la _Pyrochroa
coccinea_. Appareil digestif. (Ibid., Sér. 2, Zool., xiii, 1840, pp.
328–330, 334–337, 2 Pls.)

—— Histoire comparative des metamorphoses et de l’anatomie des
_Cetonia aurata_ et _Dorcus parallelepipedus_. Appareil digestif.
(Ibid., Sér. 2, Zool., 1824, xviii, pp. 174–176, 2 Pls.)

—— Anatomie générale des Diptères. Appareil digestif. (Ibid., Sér. 3,
Zool., i, 1814, pp. 248, 249.)

—— Histoire des métamorphoses et de l’anatomie du _Piophila
petasionis_. Appareil digestif. (Ibid., Sér. 3, Zool., i, 1844, pp.
372–377, 1 Pl.)

—— Études anatomiques et physiologiques sur les insectes Diptères de
la famille des Pupipares. Appareil digestif. (Ibid., Sér. 3, Zool.,
iii, 1845, pp. 67–73, 1 Pl.)

—— Recherches sur l’anatomie et l’histoire naturelle de l’_Osmylus
maculatus_. Appareil digestif. (Ibid., Sér. 3, Zool., ix, 1848, pp.
346–349, 1 Pl.)

—— Études anatomiques et physiologiques, et observations sur les
larves des Libellules. Appareil digestif. (Ibid., Sér. 3, Zool.,
xvii, 1852, pp. 101–108, 1 Pl.)

—— Recherches anatomiques sur les Hyménoptères de la famille des
Urocerates. Appareil digestif. (Ibid., Sér. 4, Zool., i, 1854, pp.
212–216, 1 Pl.)

—— Fragments d’anatomie entomologique. Sur l’appareil digestif du
_Nemoptera lusitanica_. (Ibid., Sér. 4, viii, 1857, pp. 6–9, 1 Pl.)

—— Recherches anatomique et considerations entomologiques sur les
Hémiptères du genre Leptopus. Appareil digestif. (Ibid., Sér. 4,
Zool., 1858, x, pp. 352–356, 1 Pl.)

—— Recherches anatomiques sur l’_Ascalaphus meridionalis_. Appareil
digestif. (Ibid., Sér. 4, xiii, 1860, pp. 200–202, 1 Pl.)

=Leydig, F.= Zur Anatomie von _Coccus hesperidum_. (Zeitschr. f.
wissens. Zool., v, 1853, pp. 1–12, 1 Taf.)

=Lubbock, J.= On the digestive and nervous System of _Coccus
hesperidum_. (Proc. Roy. Soc., ix, 1886, pp. 480–486; also Ann. Mag.
Nat. Hist., 1859, Ser. 3, iii, pp. 306–311.)

=Scheiber, S. H.= Vergleichende Anatomie und Physiologie der
Œstriden-Larven. V. Das chylo- und uropœtische System. (Sitzber. d.
k. Akad. d. Wissens. Wien. Math.-naturwiss. Cl., 1862, xlv, pp.
39–64, 1 Taf.)

=Gerstaecker, A.= Bronn’s Klassen und Ordnungen des Tierreichs. V.
Gliederfüssler. (Ernährungsorgane, pp. 87–105.)

=Graber, V.= Zur naheren Kenntnis des Proventriculus und der
Appendices ventriculares bei den Grillen und Laubheuschrecken.
(Sitzber. d. k. Akad. d. Wissensch. Wien. Mathem.-naturwiss. Cl.,
lix, 1869, pp. 29–46, 3 Taf.)

—— Ueber die Ernährungsorgane der Insekten und nächstverwandten
Gliederfüssler. (Mitteil. d. naturwiss. Vereins für Steiermark.
Graz, 1871, ii, pp. 181, 182.)

—— Verdauungssystem des Prachtkäfers. (Ibid., Graz, 1875.)

—— Die Insekten., i, 1877. (Verdauungsapparat, pp. 308–328.)

=Wilde, K. F.= Untersuchungen über den Kaumagen der Orthopteren.
(Archiv f. Naturgesch., xliii Jahrg., 1877, pp. 135–172, 3 Taf.)

=Simroth, H.= Ueber den Darmkanal der Larven von _Osmoderma eremita_
mit seinen Anhängen. (Giebel’s Zeitschr. f. d. ges. Naturwiss.,
1878, li, pp. 493–518, 3 Taf.)