

THE ORGAN OF TASTE. 373 



just as irritants act on the soft tongues of the mammalia ; they may thus give 

 warning of danger. 



In the soft-skinned Mollusca, Molluscoida, Annelida, and Coelenterata, the 

 outer layer of the integument does not consist of flattened epidermoid scales, 

 but of soft spheroidal cells with thick walls, often covered with a structureless 

 membrane. The laminated shells of these animals, when they exist, are 

 formed by the calcification of a nacreous excretion from the surface of the 

 true skin beneath the thin epidermis, which is best seen at the growing margin 

 of the shell. The calcareous substance is almost entirely carbonate of lime. 

 The shell of the tunicated Molluscoida is formed, not by excretion, but by the 

 conversion of their cellulose integument, into structures resembling shell, car- 

 tilage, bone, or even dentine. (Huxley. ) 



The calcareous shell of the larger Crustacea, the horny coverings of others, 

 the chitinous integument of the Myriapoda and many of the Insecta, and the 

 coriaceous skin of the Arachnida, are sub-epidermic structures, formed by 

 various thickenings, fibrillations, calcifications, and other changes of the epi- 

 dermis, and of certain layers excreted beneath it. The spines, hairs, and mi- 

 croscopic scales of Insects are epidermic. 



Cutaneous glands are represented in the non-vertebrate animals, by peculiar 

 csecal follicles and tubes found in a few Annelida, Insecta, and Mollusca. The 

 chromatophores of certain Mollusca, and the thread-cells of the Coelenterata, 

 are not glands. 



The nervous substance of the warm- and cold-blooded animals must be 

 adapted to suit very different ranges of temperature. 



THE SENSE OF TASTE. 



The Organ of Taste. 



The tongue is the organ chiefly concerned in the sense of taste; 

 other parts of the mouth, however, especially the under surface of the 

 soft palate, and the anterior pillars of the fauces, are also endowed 

 with this sense. 



The tongue is a muscular, vascular, and nervous organ, made up of 

 two symmetrical halves, joined in the middle line. It is composed 

 chiefly of muscular fibres, some of which are proper to it ; but the 

 greater number proceed from other parts, to its base and under sur- 

 face. The apex, sides, upper surface, and forepart of the under surface, 

 are free ; by its under and back part, it is attached to the lower jaw, 

 the hyoid bone, and the styloid process of the temporal bone ; it is 

 also connected with the pharynx and soft palate, by means of the an- 

 terior and posterior pillars of the fauces; and lastly, it is connected 

 to the epiglottis and neighboring parts, by reflections of the mucous 

 membrane of the mouth. A fold of this membrane, seen beneath the 

 tip of the tongue, forms ihefrcenum linguae. The apex of the tongue 

 is thinner and narrower than the rest of the organ ; the dorsum, or 

 upper surface, is convex, and presents along the middle line a furrow 

 called the raphe, which ends behind in a depression, the foramen 

 ccecum. 



The dorsum, edges, and tip of the tongue, have a peculiar rough 

 appearance, differing altogether from the smooth character of the 

 mucous membrane covering its under surface and the rest of the inte- 

 rior of the mouth, and depending on the presence of little eminences, 

 named papillce. These somewhat resemble the papillae of the skin, 



