GENERAL ANIMAL FUNCTIONS. 



93 



temperature are, in the highest animals, more or less 

 diffuse skin senses. The chemical sense has become, in 

 the highest animals, localized about the head and its 

 appendages, often in the mouth. We know it as taste 

 and smell. Sensitiveness to light is highly concentrated 



FIG. 17. Diagram of types of nervous end organs. From various sources, i, a 

 tactile bristle (insect); 2, pit-like organ with a sensory cell (s), olfactory (fly); 3, a 

 complex taste bulb with sensory cells (mammal) ; 4, an otocyst, organ to give knowledge 

 of the direction of the pull of gravity, and of vibrations (mollusk). b, protecting 

 bristle; h, hair; n, nerves; o, otolith; p, sensory pit into which the sensory cell protrudes; 

 s, sensory cells. 



Questions on the Figure. What evidence can you give that these 

 are sensory organs? Discuss the difference in their mode of receiving 

 their stimuli. 



in organs known as eyes, usually confined to the head. 

 Beside these there is, in many animals, a localized sense 

 of hearing, and a kind of gravity (or equilibrium) sense 

 possibly associated with hearing in its evolution. 



