40 LESLIE B. AREY 



for a short time; in this event, however, another reversal soon 

 restored the former orientation and the normal direction of 

 continued movement was plainly with the anterior end in front. 

 When the posterior end was stimulated the animal sprang 

 forward and if it continued to swim, it proceeded head fore- 

 most, although subsequent reversals usually occurred from time 

 to time. 



One lancelet of this set was especially instructive ; after stimu- 

 lation and the usual energetic response, it would continue swim- 

 ming at a rate of about 1 cm. per second for a considerable 

 distance without reversal; in several instances it more than 

 circumnavigated the dish, a distance of over a meter, yet the 

 anterior end was always carried in advance. Several other 

 animals showed the same behavior but in a less degree; in general, 

 after several responses the reaction was as long but less vigorous 

 than that of a rested animal, and hence was easier to observe. 



A circular trough 30 cm. in diameter, 0.5 cm. wide at the 

 bottom and 1.25 cm. wide at the top was constructed by placing 

 a porcelain pan, bottom up, inside a slightly larger pan; the 

 purpose of this arrangement was to give the animal free swimming 

 room but to limit its locomotion to one direction. The results 

 were in agreement with those described previously; it was im- 

 possible to make an Amphioxus swim backward for more than a 

 few centimeters before somersaulting and forward locomotion 

 occurred. 



A final method, which gave more conclusive evidence concern- 

 ing the orientation of the animal during normal locomotion in 

 unlimited space, consisted in treating one end of the lancelet's 

 body with an intra vitam stain, whereby through direct obser- 

 vation one could be certain of the animal's orientation even 

 during the wild dashes that often occur. Objections may be 

 raised to the artificial conditions of the experiments described 

 above, which were devised for limiting the animal's move- 

 ments; thus it is entirely possible (although I do not believe it 

 to be actually the case) that Amphioxus has a more complicated 

 swimming behavior in the open than when locomoting in close 

 quarters where some of its movements, including perhaps back- 



