446 Journal of Comparative Neurology and Psychology. 



but is oblique. This obliqueness in the stroke of the cilia is 

 easily rendered evident by mounting the animals in water con- 

 taining a large quantity of India ink in suspension, as described 

 above. After the violence of the movement has subsided, 

 specimens may be studied that are restrained by coming in con- 

 tact with a solid, or by swimming into a crevice. In such speci- 

 mens, still revolving on the long axis, it may be seen that the 

 particles of India ink on the upper surface of the animal pass 

 backward and, when the anterior end is directed away from 

 the observer, to the observer's right. That is, on the right 

 side of the animal the particles pass toward the oral groove, 

 on the left side away from the oral groove (Fig. i). This 



'V\\V) 



M 



Fig. I. Diagrams showing the direction of the water currents caused by 

 the cilia, in different positions of the animal, a, aboral surface; b, right side ; c 

 left side ; d, oral surface. 



movement is indicated in a transverse section of the animal by 

 Fig. 6, a. It is evident that the ciliary motion thus indicated 

 would turn the animal in the opposite direction from the cur- 

 rents — that is, over to the left. In the oral groove the cilia 

 strike more nearly directly backward, with but a slight oblique- 

 ness that is opposite that of the body cilia. This is shown by 

 the fact that a current runs within the groove from its anterior 

 to its posterior end (Fig. i, b, c, d). 



The swerving toward the aboral side is due, in the normal 

 swimming, largely to the more powerful stroke of the cilia in 



