SENSE-ORGANS OF THE INTEGUMENT 255 



In Mammals, organs of taste are still found on the soft palate, 

 on the walls of the pharynx, and even extend into the larynx ; but 

 they are most numerous on the tongue, where they occur on the 

 circumvallate and fungiform papillae as well as on the papilla 

 foliata. 1 



Thus the specific integumentary sense-organs of aquatic Verte- 

 brates have not entirely disappeared in terrestrial forms, certain of 

 these (end-buds) being retained even in Mammals, under the 

 necessary condition of a moist medium. 2 



c. Tactile cells and corpuscles. 

 (Terminal ganglion-cells.) 



In these structures there is no longer any direct connection 

 with the surface of the epiderm, and supporting cells are wanting. 



" Tactile spots," consisting of groups of tactile cells, are met with 

 for the first time in tailless Amphibians, in which they are 

 usually situated on small elevations, and are distributed over the 

 skin of the whole body (Fig. 187, A). Phylogenetically they are 

 probably derivable from the integumentary sense-organs of the 

 Ichthyopsida. In Reptiles, amongst which they retain the simplest 

 form in Hatteria and are arranged along the margins of the scales, 

 they are found chiefly on the lips and sides of the face and on the 

 snout, but in some cases (as in Blindworms, Snakes, and young 

 Crocodiles) they are present on the scales over the whole body, 

 and are usually arranged symmetrically. In Snakes and Birds 

 the tactile cells are confined to the mouth-cavity (tongue) and to 

 the beak (cere), and are much closer together, forming definite 

 masses, or tactile corpuscles. Each of these is surrounded by a 

 nucleated connective tissue investment from which septa extend 

 into the interior, partially separating the individual tactile cells 

 from one another : the " Grandry's corpuscles " occurring on the 

 beak (Fig. 187, D) are modified tactile corpuscles. 



In Mammals the tactile cells are either isolated as, for instance, 

 on the hairless portions of the body, or they give rise to oval 

 corpuscles, each consisting of a many-layered and nucleated invest- 

 ment, into which a nerve passes, becomes twisted up, and comes 

 into relation with one or more terminal cells (Fig. 187, B, c). These 

 are most numerous and highly developed on the volar and plantar 



1 Two circumvallate papillae are present in Monotremes, three in Marsupials, 

 and a variable number in the Eutheria. Foliate papillae are especially well 

 developed in Rodents, but in many Mammals are little marked or wanting. The 

 relative functional importance of the different kinds of papillae varies in the 

 course of the individual life in Man. In Cetaceans (e.g. Dolphin) only vestiges 

 of the gustatory organs are retained. 



2 Nothing is known as to whether certain of these organs in lower Verte- 

 brates are concerned with the sense of taste, or whether a change of function has 

 taken place in passing to the higher forms : the nerve-supply is, however, 

 interesting. 



