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.