ORGANS OF DIGESTION IN THE INVERTEBRATA. 67 



dermata afford in the structure of their digestive organs, connecting 

 links of transition from the radiated to the articulated classes. In 

 the higher forms of the echinida strong masticating and salivary- 

 organs are provided, the anal orifice, which in the lower tribes is 

 placed on the inferior surface, gains a dorsal aspect, which it con- 

 tinues to hold in the holothuriae and articulated classes. Thus we 

 perceive the digestive cavity, from being a simple monostome sac, 

 gradually acquires the form of a long narrow canal, open at both 

 ends, and furnished with salivary and biliary organs. 



Diplo-neura, Grant — Articulate Cuvier. — The carnivorous 

 character of this great division of the animal kingdom bespeaks an 

 alimentary canal, limited in its capacity, straight in its form, and 

 simple in its structure. This canal usually takes a horizontal 

 direction, opens at the two opposite extremities of the body, and is 

 provided at its commencement with prehensile, destructive, or mas- 

 ticating organs. In consequence of the simple nature of the food 

 on which the entozoa subsist, many of them have but a single orifice 

 to their digestive sac. In the higher and more perfect forms, how- 

 ever, of these as well as of the rotifer a, the canal passes straight 

 or slightly winding through the body, presenting an oral and anal 

 aperture, and surrounded by the genital and biliary organs. The 

 cirrhopoda are remarkable for the great size of their salivary and 

 biliary apparatus, and the wide ducts of the latter, which open into 

 the stomach, as in most of the invertebrated tribes. 



Among the annelida the earth-worm is remarkable for its capa- 

 cious mouth, a small salivary gland, a sacculated stomach, consist- 

 ing of three continuous cavities, and a narrow, slightly bending 

 intestine. The leech has three horny maxillae, furnished with sharp 

 teeth, with which it inflicts its tri-radiate wound, the straight, irre- 

 gularly sacculated intestine is furnished with ten pairs of lateral 

 coeca, and enlarges into a small sac near ihe anus. The carnivo- 

 rous rnyriapods are provided with three pairs of salivary and two 

 poison-glands, by their contracted oesophagus and elongated mem- 

 branous stomach, they resemble the higher species of worms, and 

 by their small, narrow intestine, ending in a wide colon, they are 

 allied to the ophidian reptiles. 



The digestive organs of the insecta present in an embryo state 

 nearly all the essential elements of the chylo-poietic system in the 

 highest classes of animals, as masticating organs, salivary and 

 mucous glands, liver, pancreas, &c. : they will be found to vary, 

 however, according to the peculiar living habits of the species, and 

 the quality of their food. The alimentary canal usually consists 

 of a wide pharynx, a narrow oesophagus, a dilated crop, a muscular 

 gizzard, provided with sharp, conical, horny teeth, a capacious chy- 

 lific stomach, a straight, narrow intestine, a short, dilated colon, 

 and a contracted cloaca. In the herbivorous insects, the alimentary 

 canal is long, capacious, and complicated. The gall-bladder is 

 usually single, but occasionally double. The cunning carnivo- 

 rous aracknida resemble the insects in the arrangement of their 



