COMPARATIVE PHYSIOLOGY OF DIGESTION. 345 



dibulae) exceed the lower (maxillae) in strength. In sucking-insects the four 

 jaws are transformed into a long tube with a longitudinal slit (the stinging pro- 

 boscis of the bed-bug), which lies in the semicircularly grooved lower lip as in 

 a case. The proboscis of the butterfly consists of the greatly prolonged lower 

 jaws, lying side by side, and capable of being rolled up, while the development 

 of the upper jaws has been arrested. Bees have a sucking tongue, which lies 

 in a groove formed in the lower jaws; in addition, the feeble upper jaws still per- 

 sist as organs of mastication. 



In crustaceans the esophagus is short; in some the stomach is a simple dila- 

 tation, in others it possesses diverticula, in which are situated the bile-producing 

 glands. The fresh- water crab and its relatives possess a strong chitinized in- 

 tima in the stomach, which is capable of acting as a masticating organ. This 

 membrane is expelled when the skin is shed. Among arachnids, scorpions have 

 a simple alimentary canal. True spiders possess a narrow esophagus and a 

 circular stomach; in addition diverticula on all sides, at the base of which liver- 

 tissue is present, and which may extend even down into the feet. In insects, 

 in addition to the esophagus and the chyle-stomach, generally rich in glands, 

 and at times serrated, there are present various portions, such as the crop in 

 the cricket for instance, the sucking stomach in the butterfly, the masticating 

 stomach in the beetle, in varying manner. The intestinal canal is usually shorter 

 in carnivorous than in herbivorous insects. In the intestine of the flour- worm 

 (tenebrio) ferments are present resembling those of the pancreatic juice. It 

 is remarkable that, in the larval state, as, for example, of most bees, the tract is 

 closed below the chyle-stomach. The rectum, with its auxiliary apparatus, exists 

 by itself and empties, as an excretory duct, into the anus. Peculiar long, tubular 

 excretory organs, the Malpighian vessels, several of which are present, open at 

 the junction of the small and the large intestine. 



Of the vermes, tape-worms, as well as the acanthocephala (echinorhynchus) 

 among round worms, have no special digestive organ, but are nourished byendos- 

 mosis, through absorption on the part of the skin. The anus is wanting in 

 trematodes (distomum), thread-worms, and almost all turbellaria. In the first, 

 as well as in leeches (sanguisuga) , the buccal orifice is surrounded by a sucking- 

 cup, which, in leeches, possesses, in its depth, three dentated cutting organs. 

 Some leeches, as well as the planaria, have a protrusile proboscis. The intestine 

 of turbellaria, unprovided with an anus, is shaped simply like a glove-finger. It 

 is variously branched in liver-flukes (distomum) . In the annulate worms the in- 

 testine extends from the anterior to the posterior extremity of the body; both 

 mouth and anus are present. Among them, the earth-worms possess a muscular 

 pharynx, while leeches have a highly distensible stomach, provided with many 

 lateral diverticula, which, when the animal has sucked itself full, can be incised 

 through the skin of the back, so that the blood flows continuously from the wound, 

 while the animal continues to take up blood through its sucking mouth (bdel- 

 lotomy) . All vermes are unprovided with a liver. 



All echinoderms possess an intestinal canal. The mouth is often provided 

 with a biting mechanism, which appears in sea-urchins in the form of five enamel- 

 teeth connected with a movable, complicated maxillary apparatus (Aristotle's 

 lantern) . Many of the starfish are unprovided with an anus ; a bile-like secretion 

 is found in diverticula of their stomach. Salivary glands have been found in 

 sea-urchins. 



The aquatic celenterates possess no intestinal tract provided with independent 

 walls. The abdominal cavity is the digestive cavity; mouth and anus are repre- 

 sented by the same central orifice, which often is surrounded by tentacles (med- 

 usae, polyps)! A system of canals, passing through the body (medusa?), and con- 

 nected with the digestive cavity, conveys the nutritive fluid and, at the same 

 time, the oxygen-containing water. It is, therefore, the water- vascular-system, and 

 at the same time the nutritive, respiratory and excretory organ. 



Among the protozoa, the gregarines are nourished by endosmosis through 

 the skin. Infusoria possess mouth and anus, although their abdominal cavity 

 is bounded only by the protoplasm of their body-substance. Rhizopods surround 

 their food with their body-substance and excrete the indigestible material at 

 another portion of the body. In sponges this process takes place from the in- 

 terior of their numerous canals, which penetrate the colonies of their protoplasmic 

 bodies. 



Digestive Phenomena in Plants. The observations upon the digestion of 

 proteid on the part of a number of plants are highly remarkable. The sundew 



