PEDAL LOCOMOTION IN ACTINIANS 113 



other individuals the line of locomotion in each case was obHque 

 to this axis. 



These preliminary observations made it quite clear that the 

 actinians under consideration not only do not creep invariably in 

 a direction corresponding to their secondary axis, but that their 

 directions of locomotion bear no simple relations to such axes. 

 Is this relation constant for each individual, or does it change 

 from time to time in the same animal? An answer to this ques- 

 tion was sought in the two more easily controlled species. Acti- 

 nia bermudensis and Sagartia luciae. Actinia bermudensis when 

 placed in a large, flat-bottomed, glass dish is very hkely to at- 

 tach itself quickly to the glass surface and begin creeping. The 

 directions of its movements are by no means constant. How di- 

 verse they may be can be indicated by the records from a single 

 animal. Designating the direction of the secondary axis in this 

 animal as north and south, the successive creeping movements 

 made by it were found to be as follows : Five movements one after 

 another were first taken in what would correspond to a westerly 

 direction, then one to the northwest, followed by one to the 

 north, after which the animal made three movements to the 

 southwest, then three to the west, and finally two midway be- 

 tween west and southwest. All these movements were car- 

 ried out without shifting the secondary axis from its original 

 north-south direction. 



Still more conclusive results were obtained from Sagartia luciae, 

 which I have had the opportunity of working on since the pub- 

 lication of my preliminary note (Parker, '15). This species is 

 negatively phototropic^ and the direction of its movements can 

 be controlled easily by changing the direction of the light. A 

 monoglyphic specimen was induced by a beam of strong light to 

 creep in the direction of its secondary axis. The fight was then 

 shifted through 90 degrees, and in about 10 minutes the ani- 

 mal had changed its course correspondingly but without turning 

 its body. It was thus induced to creep at right angles to this 

 axis. The fight was next set at about 45 degrees to its first 



^ Contrary to the statement made by Hargitt ('07, p. 280) I have found Sa- 

 gartia luciae very responsive to light. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 22, NO. 1 



