LOCOMOTION OF STICHOPUS PANIMENSIS 207 



As each locomotor wave in Stichopus represents a region of 

 freedom from the substrate to which the remainder of the 

 trivium is temporarily attached, and as each wave progresses 

 from the hind end of the animal to the head, the locomotion of 

 this echinoderm reproduces the essentials of that type of gastro- 

 pod locomotion which has been designated the direct mono- 

 taxic type (Vies, '07). This type is well shown in Helix (Parker, 

 '11), though for comparison with Stichopus certain sea-anemones 

 (Parker, '17 a) are better, for in these forms, as in Stichopus, 

 only one wave at a time occurs on the foot as contrasted with 

 the numerous waves seen in Helix. For the analysis of this 

 type of locomotion Stichopus is a particularly satisfactory form 

 to study because of the grossness of its movements. In this 

 holothurian there can be no question that in the region of the 

 locomotor wave the foot is lifted well above the substrate, a 

 point that cannot always be easily seen in gastropods. And, 

 further, in Stichopus the means by which the foot is attached to 

 the substrate does not have to be inferred as in the case of some 

 gastropods, but is to be directly observed in the ambulacral 

 feet of the holothurian. In both these respects Stichopus is a 

 more favorable animal for the analysis of this general type of 

 locomotion than even Aplysia (Parker, '17 b), in which the 

 temporary elevation of the foot and its subsequent attachment 

 to the substrate can be seen with unusual clearness. 



SUMMARY 



stichopus panimensis creeps on its trivium by means of loco- 

 motor waves of a direct monotaxic tj^pe. 



These waves progress over the animal at a rate of about 0.39 

 centimeters per second and enable the animal to creep a meter 

 in about 15 minutes. 



The part of the trivium moved forward is lifted well above 

 the substrate to which the remainder of the trivium is attached 

 bv the ambulacral feet. 



