into the stomach by alternate constrictions which travel along its length, driving the contents before them.

In the stomach, however, a different arrangement of the muscular coat is required, for here not only must the food be passed along, but it must be moved about and turned over as well, so as to enable all parts of its mass to come in contact with the digestive fluids.

In order to facilitate this, transverse, and also longitudinal, and some diagonal fibers are present, thus rendering possible a changing of dimension in any direction.

The small intestine in the caterpillar is reduced to a mere short passage, connecting the stomach with the colon or large intestine, and its other functions are for the most part performed by the stomach itself.

The large intestine is found to consist of a rather short tube with two dilations, and as no secreting glands pour their products into it, its only function appears to be one of absorption.

From the colon the refuse passes into the cloaca, the rectum, and thus into the extreme. We find on closer examination at least two sets of glands present, one having its origin in the head, and the other attached to the alimentary canal at the posterior end of the chylific ventricle. The first are salivary glands and consist of two pairs of tube-like organs, one pair for the secretion of ordinary saliva to aid in digestion, and the other sometimes so metamorphosed as to become a spinning organ for the secretion of silk, by means of which, in the cocoon-making forms, the whole or a part of the habitation is constructed, in which the insect, as a pupa, awaits its development into the imago state.

These glands are often very long, for a part of their length at least dilated to form a tube of larger diameter, which serves as a reservoir, and more or less coiled or bent back on themselves, occupying sometimes a considerable portion of the body cavity.

The other glands are malphigian vessels or urinary tubules, as their entire function seems to be of an excretory nature. They are long, hair-like, with little bead-like dilations occurring at close intervals along their length; but their most striking feature is their great number, as they often form a complete network around the alimentary canal.

Fig. II. shows the digestive tract of an orthopterous insect, the grasshopper, Acridium obscurum, also mandibulate in type.

In general, we have again the comparatively straight tube with little or no bending, yet one which shows more of a differentiation into separate regions, each with its own function.

The oesophagus is short, leading from a mouth with well-defined jaws, which are very powerful in their working.

Next we have a large crop, a structure which was absent in the preceding specimen, and whose use is obviously that of a food-reservoir. The orthoptera in general are very rapacious feeders and the jaws do the work of breaking up their food only partially, hence it must be stored in this very suitable place until it can be made finer and better fitted for digestive purposes by the gizzard.

The crop is a large, distensible muscular organ, on whose inner surface may be seen "numerous transverse wrinklings and ridgings gradually changing to a longitudinal form, and these in turn break up into little conical teeth toward the end of the crop, to change again to a plate-like structure at the constriction before the opening into the stomach. There is no distinctly-developed gizzard, the end of

the crop performing that function."

As the food now enters the stomach in its finely-ground condition, it is bathed by a liquid secreted by the cæca or cæcal tubes, six of which lie at this point, extending pouch-like anteriorly and tube-like posteriorly.

This secretion, by its digestive process, renders the contents of the stomach very similar to the chyle of the higher animal.

As before, some absorption takes place in the stomach, and almost all in either the stomach or intestine, the colon being merely to prepare the rejected portion for the rectum.

Beside the cæcal glands there are salivary glands, secreting an acid, dark-colored liquor, the so-called "molasses," which probably has a defensive function as well as that of aiding digestion. The usual malphigian vessels are present, and also some anal glands, whose function probably is that of lubricating the posterior passages to facilitate the passage of excreta.

Passing on from those insects mandibulate in character, we take up the haustellate species, treating first the butterfly, Danias plexippus. Fig. III.

Before entering into a detailed description of the insect it might be well to state that after the imago stage of an insect is reached its only duty is the propagation of its kind, and the true life of the animal,

that in which it spends most of its time, eating and growing, is the larval stage. So true is this, that in many insects whole families sometimes, especially among the lepidoptera and May-flies, the digestive systems and mouth parts in the imago are so far aborted as to become wholly useless for feeding. Again, in others, as in the elmleaf beetle, where the insect hibernates through the winter in the imago form, food is taken in fall solely to store up fat for winter use, and in the spring only until sexual maturity is reached, when the insects mate, oviposit and die.

Returning to our butterfly, we find the mouth parts formed into a long proboscis, coiled up at rest, but capable of being thrust to the depths of the flower-cup to sip the nectar or honey found therein. Leading from the mouth through the thorax is the long, slender œsophagus, which divides, one portion leading into the food-reservoir, the other into the stomach. The food-reservoir corresponds in function to the crop as a place of storage, though instead of being a simple dilation of the canal through which all food must pass, it is a sort of bladder-like outgrowth to contain only that portion of food which cannot make its way directly to the stomach-the surplus, in other words.

The chylific ventricle is a straight tube of considerable capacity, but lacking entirely any cæca or gizzard-like structures at its entrance, as the absence of solids in the insect's food renders their presence unnecessary. The usual malphigian vessels are present in great numbers, being simple hair-like tubes.

The intestine is of rather small diameter, coiled at least once and ending in a good-sized, pear-shaped colon. The excrement is very small in quantity and pasty in consistency. The salivary glands are well developed, consisting of two paired, thread-like bodies opening into the buccal cavity, having but one orifice to each pair.

We next consider the fly, our sketch being made from a blow-fly, Calliphora vomitoria. Fig. IV.

Flies feed in one of two ways, either by piercing and sucking or by lapping and sucking; the fly in question being one of the latter sort, as the galea are formed into a lapping and scraping organ.

As they feed to a large extent upon solids, such as sugar and other substances, means must be provided to reduce these to a liquid state by solvents before they can be taken into the mouth.

Hence we have a very large development of the salivary glands,

and a correspondingly large secretion of saliva for this glands are thread-like and coiled into a tangled mass.

purpose. The

There is also a sort of bladder for the storage of the saliva. The œsophagus is long and slender, as in the preceding species; the crop a dilation directly upon the canal itself, not like the outgrowth in the butterfly. The chylific ventricle is not very long, and of small capacity compared with those of our preceding species.

There is no evidence of either cæca or gizzard, but the malphigian glands are well developed, perhaps not so numerous as those we have seen, but larger, and resembling those of the caterpillar with their bead-like dilations.

The intestine is long, coiled, but simple in structure, and opens into a curiously-shaped colon. Fig. VII.

The colon is somewhat rectangular in shape, with four large lobes, one at each corner, but inclining from the anal extremity. The rectum is longer than usual, being fully equal in length to the colon, and its excrement is similar to that of the butterfly. In either case the material hardens almost as soon as voided.

Lastly we have the digestive system of the bumble-bee, Bombus sp., and here we find the greatest length and sharpest differentiation into separate regions. Among the Hymenoptera, to which order the bees belong, we find not only the haustellate, but mandibulate type represented as well, hence we should expect to and do find traces of characteristics of both.

Here again we find the long œsophagus extending through the thorax, which indeed seems to be the rule; the exception in the case of the grasshopper being due to the great development of the reproductive organs, which at maturity fill almost the entire abdomen, thus forcing a portion of the alimentary canal into the thorax.

The crop in Bombus is quite large, membraneous in structure and readily dilated with chitinous, plate-like structures bearing longitudinal ridges at its insertion into the stomach.

This structure is evidently a gizzard, morphologically speaking, yet as liquid food is generally taken, it is in this case apparently functionless.

The stomach is large, exceeding the capacity of the crop, with a curious differentiation in the size of its transverse striations at the anterior end. There is a total absence of cæca; but there are an

immense number of malphigian vessels almost entirely enveloping the canal as it lies closely coiled in the insect.

The intestine is of small diameter, but equal in length to the stomach, and ending in a membraneous, distensible colon. The salivary glands are fairly well developed, and have only the usual digestive function.

In summing up the characteristics of those insects we have classified as mandibulate in contradistinction to the haustellate type, we can only state general facts which seem to meet with many exceptions.

The presence of gizzard and cæca seems to indicate the mandibulate character, as they are absent in the true haustellate type. The canal, as a whole, seemed to be shorter and straighter in the case of mandibulate insects, hence of lower type than the haustellate forms.

The salivary glands were well developed in both divisions, though in the haustellate insects used solely for digestive purposes, while in the mandibulate forms with additional functions, one of cocoonbuilding or protection and the other of defense.

There is in the haustellate type in some instances a modification of the pharynx, the so-called sucking stomach, by whose aid liquids are drawn into the mouth.

In the case of the mandibulate forms we may find in the receum certain moulding appliances, which give to the pellet of excreta a characteristic form by which often the insect may be determined, while in the haustellate type no such modification exists, as no impression could be left on liquid excrement.