Taste sensitivity and the structure of the taste organs differ greatly in the mammals, but there seem to be two characteristics in common, namely, the localization of the taste corpuscles within the mouth and the importance of the tongue in arousing taste sensations. The character of the mucous lining of the mouth also shows great variation in the number of papillæ and the taste buds which they contain. The number of papillæ varies from two or three in the marsupials and four in the elephant to an extremely large number in rodents, e.g., the rat. The papillæ are in general quite similar to the three most common forms in the human taste organs, the circumvallate, the fungiform, and the filiform, and have about the same location in relation to each other. The greatest difference is in the prominence of the fourth type, the foliate papillæ in certain mammals, as compared with man. These are seen best in the rabbit, as folds directed downward and forward on the sides of the tongue in its posterior portion. They have been considered to result from the great number of papillæ which throw the mucus into folds. Each foliate papilla is composed of a number of parallel ridges, each ridge in turn being composed of papillæ of the fungiform type. Between the ridges there are narrow ditches. It is in the side walls of these that the taste corpuscles are found in greatest numbers. Thus, these ditches are analogous, in function at least, to those of the circumvallate papillæ. Their origin, however, seems to be different from that of the circumvallate. In the monkey one finds less prominent folds on the sides of the tongue, rich in taste corpuscles, which represent the foliate papillæ. The taste corpuscles themselves have about the same characteristics in all mammals as in man. There are differences in size, to be sure, but their structure is the same, and the supporting cells, gustatory cells, and nerve fibers are present in them all. This survey of taste in the animal kingdom suggests the conclusion that the taste organs represent a modification of the original skin sensitivity or touch sense, and surely a slight modification when compared with the senses of sight and hearing. A certain resemblance has been remarked by Wundt and others between the touch corpuscles and the gustatory corpuscles. His interpretation is that the whole body was originally endowed with the touch sense, while certain parts being affected continually by specific sorts of stimuli, became adapted to them by undergoing modifications of structure. The head or mouth end of the animal was more subject to chemical stimulation, and the adaptation of the tactile organs to this particular form of stimulation resulted in the development of the senses of taste and smell. To consider taste as one of the lower senses, in the sense of being least highly developed and the earliest to appear, is justified from this survey of the evolution of the taste sense, if from no other point of view.