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



HARVARD COLLEGE. NO. 259. 



THE ORIENTATION OF AMPHIOXUS DURING 

 LOCOMOTION! 



LESLIE B. AREY 



Observers have differed regarding the question as to which 

 end of Amphioxus is in advance during swimming. Rice ('80, 

 p. 8) seems to have been the first to record observations on 

 this subject: 



These movements were executed sometimes upon the back, sometimes 

 upon the abdomen in the position of ordinary fishes, it seemed to make 

 very httle difference which side was uppermost, but I have never seen 

 them move backwards or tail-end foremost. After circumnavigating 

 the vessel once or twice gradually moving slower and slower, they would 

 stop and sink down upon the sand at the bottom. 



In a more general statement Steiner ('86, p. 497) came to the 

 same conclusion as Rice, "sie stellen sich so auf, dass ihre Breit- 

 seite in die verticale Ebene fallt und rasch entfliehen sie (from 

 the stimulus) mit grosser Geschwindigkeit, das Kopfende voran, 

 indem der Korper schlangelnde Bewegungen macht, an denen 

 der Kopf nachweisbar theilnimmt. " Two years later ('88, p. 41) 

 he expressed the same opinion in almost identical language. 



Parker ('08, p. 441) took the opposite view: 



The locomotion of amphioxus is a rapid, curiously irregular wriggle, 

 often accompanied with somersault-like movements which make it 

 impossible to be sure at any moment whether the animal is swimming 

 backward or forward. The results of momentary stimulation, however, 

 show very conclusively that amphioxus can swim both backward and 

 forward, and that the direction of swimming at the beginning of any 

 course is dependent upon the part of the animal's body that was stimu- 

 lated. But how long amphioxus keeps to one form of movement 

 I was unable to discover. The fact that it usually buries itself in the 

 sand tail first leads me to believe that, though it can swim forward, 

 as maintained by Rice and by Steiner, it usually swims backward. 



' Contributions from the Bermuda Biological Station for Research. No. 36. 



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