186 THE ELEMENTARY NERVOUS SYSTEM 



direction of the stimulated tentacle, and the distal ten- 

 tacles may likewise become active. To a still more vig- 

 orous stimulus, not only do the parts of the hydranth re- 

 spond, but the stalk may contract (Torrey, 1904 b). Thus 

 impulses to motion may spread from a single proximal 

 tentacle to any part of the body. The same is true of the 

 proboscis and of the distal tentacles. Conversely, by 

 stimulating the stalk, responses can be called forth from 

 both sets of tentacles (Torrey, 1904 b). These observa- 

 tions indicate a diffuse type of transmission, such as is 

 generally assumed for a nerve-net. It is also clear that 

 the stronger the stimulus the more distant the effector 

 that can be activated. 



To ascertain something of the nature of the transmis- 

 sion, several kinds of experiments were tried. When a 

 polyp of Corymorpha is anesthetized for a few minutes 

 with magnesium sulphate or chloretone, all responses of 

 tentacles, of proboscis, and of stalk disappear except the 

 slow formation of constriction rings in the stalk. The 

 responses thus eliminated may be made to return by 

 placing the polyp for three or four minutes in pure sea- 

 water. Since the effectors that are rendered inactive are 

 the ectodermic musculature and since the drugs used are 

 known to act chiefly on nervous tissue, the conclusion is 

 drawn that the essential part of the nervous mechanism 

 of these animals must be in their outer layer, the ecto- 

 derm, a conclusion supported by the very short time 

 needed for anesthesia as well as for recovery from this 

 state. It, therefore, seems probable that nervous trans- 

 mission in Corymorpha is an affair of the ectoderm. 



To test this view, a polyp about ten centimeters in 

 length was put horizontally in an aquarium and pinned at 

 the middle of its length to a slight elevation of wax so that 



