CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY OP THE MUSEUM OF COMPARATIVE ZOOLOGY AT 



HARVARD COLLEGE. NO. 286. 



PEDAL LOCOMOTION IN ACTINIANS' 



G. H. PARKER 



ONE FIGURE 



I. INTRODUCTION 



That many actinians can creep with more or less activity by 

 means of their pedal discs over the surfaces to which they have 

 attached themselves, seems to have been known to the earhest 

 students of these animals, but aside from brief references to the 

 simple fact of creeping the Uterature contains very little concern- 

 ing this activity. The chief exception to this statement is the 

 short paper by McClendon ('06), in which the creeping of Metri- 

 dium marginatum is briefly described, and the notes made by 

 Osburn ('14) on the distances covered in creeping by this species 

 and by Sagartia leucolena. It is the object of the present paper 

 to take up this activity more fully than has been done heretofore 

 and to show in what respects it is related to actinian organization. 



The work was carried out for the most part on four species of 

 actinians: Metridium marginatum Milne-Edw. and Sagartia lu- 

 ciae Verrill at Woods Hole, Massachusetts; and Condylactis pas- 

 siflora Duch. and Mich., and Actinia bermudensis Verrill at 

 Bermuda. I am under obhgations to Dr. P. H. Mitchell, Director 

 of the Laboratory of the United States Fisheries Biological Sta- 

 tion at Woods Hole, and to Dr. E. L. Mark, Director of the 

 Bermuda Biological Station, for many courtesies shown me 

 while I was working at these stations. 



In dealing with the subject of pedal locomotion it was my in- 

 tention to find out how the direction of such locomotion is 

 related to the axes of the actinians, what the mechanics of the 

 locomotion is, and what structural conditions are present in the 

 actinians whereby this form of locomotion is made possible. 

 Of the three fundamental and mutually perpendicular axes of 



' Contribution from the Bermuda B'ological Station for Research. No. 55. 



Ill 



