COMPARATIVE ANATOMY. The first ap pearance of a salivary apparatus has been ob served by Owen,in a genus of Entozoa found in the stomach of the tiger, and named by him Gnathostoma. It consists of four elongated straight blind tubes, each about two lines in length, placed at equal distances around the commencement of the alimentary canal, having their small extremities directed forward, and opening into the mouth.± Among the Echinodermata the salivary organs in Holothuria regalis are represented by elongated cwcal processes, surrounding the cesophagus, and continued into the branched tentacles around the mouth. They exude a viscid secretion, which assists in entangling the objects which constitute the food of the animal, lubricating them, and adapting them for deglutition.
In Myriapoda the salivary glands consist of small transparent vesicles, constituting in Julus terrestris, for example, a clavate mass, the small extremity of which terminates in a twisted excretory canal opening into the pharynx. They are large and very vascular in the Scolopendridm.
In the Insecta the salivary glands evacuate themselves either into the mouth, or the com mencement of the intestine in front of the stomach.
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A. Salivary vessels opening into the mouth, generally beneath the tongue, and more seldom at the base of the mandibles.
They take the following forms : — I. Simple, long, undivided, twisted tubes : thus in the majority of insects, viz. all butterflies, many beetles and flies.
2. As a narrow vessel which empties it self into one or two bladders, whence the salivary duct originates (Nepa, Cimex, Sarcophaga).
3. As a ramose vessel with blind branches (Blaps).
4. As two long cylindrical pipes, which unite into one excretory duct.
5. As four small round bladders, each pair of which has a common duct (Pulex, Lygoeus, Cimex).
6. As a multitude of such vesicles in Nepa.
7. As capitate tubes, in the free ends of which many very fine vessels empty themselves (Taban us).
8. As tubes which at intervals are sur rounded by twirling blind bags (Ci cada).
9. As granulated glands which on each side unite into a salivary duct, both of which join into a single evacuating duct (Gry llus).
B. Salivary glands which empty them selves into the commencement of the stomach, as short or long bags, either simple or furnished with processes (Bu prestis); other forms as well as those just cited, are found among the Diptera : — I. As two capitate tubes, into the free ends of which many delicate vessels open (Hemerobius perla).
2. As two short processes of the same width as the stomach (Leptis and Acheta).
3. As two bags covered entirely with short blind processes (Bornbylius, Bu prestis).
4. As triangular processes, each edge of which is occupied by a row of vesicles (Chrysotoxum).
5. As six narrow tubes which surround the commencement of the stomach (Gryllus).
6. The blind processes which clothe the stomach in the predaceous beetles.
In Cirrhopoda the salivary glands are two in number and of considerable size, opening into the commencement of a short cesopha gus.
Among Pteropoda they are found in Clio as two long and slender glands placed at the sides of the cesophagus, and pouring their secretion into the mouth. They " present in the Gasteropoda different forms and degrees of development bearing the ordinary relations to the construction of the mouth and the nature of the food. In the Calyptrwa they are represented by two simple elongated se creting tubes. In the whelk tbey present a conglomerate structure, and are situate at each side of the cesophagus at the base of the proboscis, along which they transmit their slender ducts to terminate on each side the anterior spines of the tongue." (Owen.) In the snail they are flattened, elongated, and irregular in form, and conglomerate in struc ture, diminishing in breadth as they proceed upwards to the pharynx, where their ducts terminate. In the Vaginulus an additional slender tube whicb lies first on the stomach, passes through the nervous collar to join the duct by which the saliva is discharged.