STUDIES ON REACTION TO STIMULI. 



227 



In giving an account of the results of our experimentation, 

 matters which were described by Verworn (1889) will not be 

 dwelt upon, but the account will be confined to the points bear- 

 ing on the questions raised above. 



The operation of cutting the animals was done with a small 

 knife, under the Braus-Driiner stereoscopic binocular, which has 

 great advantages for such w r ork. It was 

 found best to cut the animals when resting 

 aeainst a clean glass surface. Most of the 



o ^> 



operations can be performed by the aid of 

 some patience without great difficulty. In 

 all cases the results set forth are drawn from 

 experimentation and observation on a con- 

 siderable number of specimens. 



i. StylonycJda. Putter (1900) gives a 

 full account of the normal movements of 

 this animal when uninjured, with a careful 

 analysis of the action of the different cilia in 

 producing the movements. For our pur- 

 poses it is important to note the following 

 different movements, (i) The animal runs 

 forward on surfaces, chiefly or entirely by FIG. i. StylonycMa, 

 the aid of the "running cilia" />, Fig. i. ventral surface, showing the 



distribution of locomotor 



(2) When stimulated it jerks back a little, organs(after patter, 1900). 

 then turns to the right or aboral side. 



This turning appears to be due to the lateral stroke of the 

 large peristomal cilia a. (3) The animal may also swim freely 

 through the water ; in doing so it swerves continually towards 

 its right side, and revolves on its long axis from right over to 

 left the resulting path being a spiral. The swerving toward 

 the right appears to be due to the lateral stroke of the peristo- 

 mal cilia, and the revolution on the long axis might well be due 

 to the same factor. 



When Styhnycliia was cut in two transversely just behind the 

 mouth, so that the entire peristome remains with the anterior half, 

 the pieces move as follows : 



i. Anterior half, possessing peristome (Fig. 2, a). After the 

 first shock effects, the movement throughout is nearly like that 



