182 THE ELEMENTARY NEEVOUS SYSTEM 



to allow of experimental tests such as have been used 

 with the stalk. Its rapid shortening from a long, narrow 

 organ to an almost spherical one (Torrey, 1904 b) and 

 its slow recovery to the elongated form, together with the 

 loss of these activities under chloretone treatment, all 

 point to a condition essentially similar to that of the 

 stalk. 



In one respect only is there an observable difference 

 between the musculature of the stalk and that of the pro- 

 boscis. Occasionally the proboscis exhibits spontaneous 

 peristaltic movements. These begin near the distal end 

 of this organ as ring-like constrictions that progress 

 toward its proximal end. The time required for a single 

 constriction to pass from one end of the proboscis to the 

 other is from half a minute to a minute. Usually not 

 more than one constriction is present on the proboscis 

 at a time. The constrictions are quite obviously due to 

 local contractions in the 1 circular muscle. They must be 

 a very effective means of mixing the contents of the di- 

 gestive cavity and probably are concerned with driving 

 some of the digestive products of the hydranth downward 

 into the stalk. A similar movement has been known for 

 some time in actinians and has been recently pointed out 

 in Metridium (Parker 1916 a). Here, as there, it is prob- 

 ably indicative of nervous supervision of a muscle other- 

 wise independent, but on this point no positive evidence 

 has been obtained. 



The proximal tentacles in a resting expanded Cory- 

 morpha radiate more or less horizontally from the basal 

 disc to which they are attached. Each tentacle curves a 

 little downward away from the mouth, but at its free end 

 it turns in the opposite direction and comes eventually 

 to point nearly outward. When stimulated mechanically 



