LOCOMOTION OF BERMUDIAN MOLLUSKS 



233 



I. Parapodial. 

 II. Pedal. 



A. Arhythmic. 



1. Ciliary. 



2. Muscular. 



B. Rhythmic. 



1. Direct. 



„ , • , rv, • (l) Alternate. ™ , 

 a. Monotaxic. b. Ditaxic. { ' _. ._, c. Tetrataxic. 



(2) Opposite. 



2. Retrograde. 



a. Monotaxic. b. Ditaxic. c. Tetrataxic. 



3. Diagonal. 



a. Monotaxic. b. Ditaxic. 



4. Lateral. 



a. Monotaxic. b. Ditaxic. c. Tritaxic. 



5. Composite. 



Parker ('14) has briefly described backward locomotion in 

 Chiton tuberculatus. I was able to study the animal's back- 

 ward locomotion in detail by allowing a Chiton to attach itself 

 by the posterior portion of the foot to the lower edge of a glass 

 plate held vertically in the air. The following record is typical. 



Experiment Four. Chiton C. Length of foot 7 cm. Attached by 1.5 cm. of 

 posterior end of foot to plate. Waves began at once. 



1st wave carries foot 0.6 cm. up plate. 



2d wave carries foot 1 cm. up plate. 



3d wave carries foot 1.1 cm. up plate. 



4th wave carries foot 1.1 cm. up plate. 



5th wave carries foot 0.1 cm. up plate. 



6th wave. Body turns and foot moves forward 0.3 cm. 



7th wave. Head against plate. Rim of shell still extending beyond plate. 

 Further turning. No forward progression. 



8th wave. Whole animal against plate. 



9th to 13th waves carry animal forward. 



In this trial the Chiton moved straight backward a distance 

 of 3.9 cm. in a series of five waves before it began to turn. In 

 many specimens turning began earlier, e.g. with the second or 

 third wave. One-fourth of the foot was the least that would 

 become attached and remain long enough for waves to carry the 

 whole foot up on to the plate. After a number of trials with the 

 same individual, the animal would finally back and turn just 



