ANIMAL PHYSIOLOGY 



71 



tb<-; 



Papilla with taste buds {i. b.) 

 from the tongue of a calf. (Greatly 

 magnified; after Loven.) 



that the special taste cell must be exposed or covered 

 only by a thin osmotic membrane, so that small particles 

 of the substance to be tasted can come into actual con- 

 tact with it. The taste organs (fig. 28) of man and the 

 other air-breathing animals are located in the mouth or on 

 the mouth parts. It is 

 also necessary that the 

 food substance to be 

 tasted be dissolved. This 

 is accomplished by the 

 fluids poured into the 

 mouth from the salivary 

 glands. With the lower Fig- 28 

 aquatic animals it is not 

 improbable that taste or- 

 gans are situated on other parts of the body besides the 

 mouth, and that taste or a sense akin to it is used not only 

 to test food substances but also the chemical character of 

 the fluid medium in which they live. 



Smelling and tasting are closely allied, the one testing 

 substances dissolved, the other substances vaporized. The 

 organs of the sense of smell are, like those of taste, simple 

 nerve-endings in papillae or pits. By smell animals can 

 discover food, avoid enemies, and find their mates. With 

 the strictly aquatic animals the sense of smell is probably 

 but little developed. There is little opportunity for a gas 

 or vapor to reach them, and only as gas or vapor can a sub- 

 stance be smelled. With these animals the sense of taste 

 must take the place of the olfactory sense. But among the 

 insects, mostly terrestrial animals, there is an extraordinary 

 development of the sense of smell. Insects must depend on 

 smell far more than on sight or hearing for the discovery 

 of food, and for becoming aware of the presence of their 

 enemies and the proximity of their mates and companions. 

 The organs of smell of insects are situated principally on 



