ORIENTATION OF AMPHIOXUS 43 



It is interesting, however, to see how near Parker was to the 

 real solution of the matter, although it must be said that the 

 whole question was not of major importance in his work; thus 

 ('08, p. 431) he says: 



When the anterior end of an amphioxus resting in a shallow dish 

 of sea water was touched even lightly with the bristle, the animal 

 usuallj^ sprang backward, though occasionally forward. The back- 

 ward spring was often accompanied by a somersault-like movement, 

 whereby the animal became turned end for end. When the stimulus 

 was applied to the posterior part of the body, the result was almost 

 invariably a forward leap. 



The somersaulting is only mentioned by him in connection 

 with the backward spring, and this I have shown is characteristic- 

 ally present at the time of reversal to normal swimming, while 

 in a forward leap it is unnecessary and is usually omitted. 



The animals mentioned above, which swam slowly for a con- 

 siderable distance in a pan of shallow water, afforded an oppor- 

 tunity to observe the movements of the body during locomotion. 

 The head and tail were bent simultaneously toward the same 

 side; the posterior of all the flexures, which is by far the most 

 prominent, occurs approximately at the level of the atriopore; 

 the next prominent flexure is at about the region of the first 

 gonadic pouches but is much less extensive than the former. 

 When swimming slowly no other flexures are evident except a 

 suggestion of one rather close behind the anterior flexure last 

 described. The occurrence of the two largest flexures just 

 anterior and posterior to the gonadic pouches suggests that these 

 pouches materially increase the rigidity of the body throughout 

 the region where they occur and thus actually determine the 

 position of the major flexures. As might be expected, when a 

 forward spring occurs the first flexure is initiated at the anterior 

 end and muscular activity extends posteriorly like a wave; 

 when an animal leaps backward the reverse is true. 



As regards orientation during locomotion, I thus conclude 

 that while Amphioxus can s\\dm backward for short distances, 

 its normal orientation in continued swimming is with the anterior 

 end in advance. 



