48 Instinct and Intelligence 



manubrium first contracts, and with unerring 

 aim brings its mouth to the point stimulated. 

 If another spot is irritated, the manubrium 

 leaves the first and moves to the second spot; 

 and when left to itself visits first one and then 

 another irritated point, dwelling on those most 

 severely irritated. (Fig. 7.) 



If the tentacles or the margin of the swim- 

 ming-bell of a Medusa (Gonionemus murbachii) 

 be stimulated by a weak electric current, a series 

 of rhythmical contractions and 

 expansions of the structures 

 forming its body and velum 

 takes place, which enable the 

 animal to swim away from the 

 source of irritation. If a small 

 bit of meat is placed in the water near one of 

 these Medusae, so as to touch more than one of 

 the animal's tentacles, they move simultaneously 

 to the food; at the same time the manubrium 

 stretches out to meet the contracting tentacles, 

 and the food is thus taken into the animal's 

 mouth and passed on to its digestive cavity. 



The movements made by the manubrium and 

 swimming-bell of the jelly-fish above referred 



