LOCOMOTION OF BERMUDIAN MOLLUSKS 231 



in other cases, all to the right or all to the left. The foot attached 

 progressively more and more of its surface to the glass, and when 

 two-thirds were adhering, it became evident that these waves 

 were the ordinary lateral waves of the anterior third of the foot, 

 and that they presented this appearance because of the con- 

 traction of the unattached portion of the foot. The interesting 

 point was that even in a given portion of the foot waves could 

 go both to the right and to the left at the same time. 



When one pushed backward with gradually increasing force 

 on the shell of Cypraea, the posterior third of the foot became 

 the same light color as the narrow band which preceded the dark 

 portion of the lateral wave, and at the same time lateral waves 

 started in opposite directions in the anterior and middle thirds. 

 Similar results were obtained when one pushed forward or to 

 the right or left on the shell, a lighter colored area appearing on 

 the side opposite to that on which the force was being applied, 

 waves likewise being set up in the rest of the foot. Like many 

 other mollusks, it was very difficult to dislodge Cypraea by a 

 steady push, but this was easily accomplished by a sudden thrust. 



The different forms of waves which may therefore appear on 

 the foot of Cypraea are (1) long lateral waves, which extend the 

 whole length of the foot and move either to the right or to the 

 left; (2) short ' lateral waves, which are about one-third the 

 length of the first, two or three sets appearing at one time, the 

 waves in any set moving either to the right or left or half of them 

 to the right and half to the left; (3) diagonal waves, which extend 

 the whole distance across the foot and move either to the right 

 or the left; (4) retrograde waves, which extend from the anterior 

 edge of the foot to the center and, of course, run from anterior 

 to posterior. 



10. Marginella arena Val. moves much faster than any other 

 marine mollusk that I examined. The average length of the foot 

 is only 1.2 cm. and it moves at the average rate of 1 cm. in 

 2.4 seconds. No waves at all were discernable on the foot of 

 this gastropod. The animal is so small and so slippery with 

 mucus, that one cannot hold it in the fingers to test the foot with 

 carmine for ciliary action. I therefore attached the shell to a 



