92 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. 



antennae in which the gangliated swollen extremities of nerves occur 

 are to be explained as olfactory fibres. In the Vertebra ta the 

 olfactory organ usually has the form of a paired pit or cavity placed 

 on the under surface of the head (nasal cavity), on the walls of which 

 the ends of the olfactory nerve are distributed. The higher air- 

 breathing Vertebrata are distinguished by the fact that in them this 

 cavity communicates with the pharynx, and by the great surface 

 extension (in a confined area) of the much-folded olfactory mucous 

 membrane. The fibres of the olfactory nerve terminate in delicate 



elongated cells, bearing 

 rods or hairs and placed 

 between the epithelial cells 

 of this mucous membrane. 

 The special sense of taste 

 is confined to the raouth 

 and pharynx. Its function, 

 from what we know of the 

 higher organisms, is to test 

 the quality of fluid sub- 

 stances, and to bring about 

 the special sensation of 

 taste. The presence of this 

 sense can be demonstrated 

 with certainty in the Ver- 

 tebrata, and it is connected 

 with the distribution of a 

 special nerve of taste, the 

 glossopharyngeal, which in 

 man supplies the tip, edges, 



Sz 



FIG. 89. a Transverse section through a cii-cum- 

 vallate papilla of a calf (after Th. W.Engelmann). 

 N, nerve; Gk, taste buds in the side-wall of the 

 papilla, PC. b, isolated taste bud from the lateral 

 taste organs of a rabbit, c, isolated supporting 

 cells (Dz) and sense cells (&) from the same. 



and root of the tongue and 



also parts of the soft palate, 

 making these parts capable 

 of the taste sensation. 



The so-called taste-buds found in special papillae (papillae circum- 

 vallatse), with their central fibre-like cells, are explained as the 

 percipient organs of this sense (fig. 89 a, b, c). Taste is, as a rule, 

 connected with the tactile and temperature sensations of the buccal 

 cavity, and also with the olfactory sensations. Finally, special organs 

 of taste appear to be present also in the Molluscs and Arthropods as 

 a specific sensory epithelium at the entrance to the buccal cavity. 

 In the lower animals the taste and olfactory organs are still less 



