76 The Animal Mind 



the existence of a specific sensation quality is furnished by 

 localized sensitiveness, for the skin of the under side of 

 the umbrella, and of the manubrium, is very sensitive to 

 mechanical stimulation, and wholly insensitive to chemical 

 stimulation, while the tentacles, as has just been stated, 

 react, by shortening and twisting themselves about the 



object, more readily to 

 chemical than to me- 

 chanical stimulation. A 

 mechanical stimulus ap- 

 plied to any part of the 

 under edge of the um- 

 brella produces after 

 from one to three 

 seconds a movement 



of the manubrium tip toward the point stimulated (519, 

 521). 



The little medusa Gonionemus murbachii (Fig. 8) shows, 

 on the other hand, two well-defined different responses to 

 special stimulation : motor reactions and food-taking 

 reactions. The motor or swimming reactions are given 

 in response to mechanical stimulation and to the presence 

 of food near the animal in the water ; but the food-taking 

 reaction occurs only in response to food (solution of fish 

 meat) ; very rarely a weak inorganic chemical stimulus 

 will produce the beginning of the response. An impor- 

 tant exception to the usual inefficacy of mechanical stimuli 

 in bringing about the feeding reaction occurs when a moving 

 mechanical stimulus is used; this very quickly produces 

 the early stages of the food-taking response. Special 

 reactions to stimuli in motion are widespread throughout 

 the animal kingdom ; their significance will be discussed 

 in the chapter on Space Perception. The food- taking re- 



