DIRECTION OF LOCOMOTION OF THE STARFISH 6 



esting to know in what direction, that is, with what ray forward, 

 these starfish would have crawled if left undisturbed after right- 

 ing themselves. The question then naturally occurs: Do star- 

 fishes naturally crawl with any particular region of the body 

 (radius or interradius) forward? It is a well known fact that 

 they 7?iay crawl with any part in advance. As Jennings ('07, 

 p. 155) put it: 



The starfish is not hampered by any considerations of anterior and 

 posterior; it may move with an}' one of its rays in the lead, or with 

 any interradius in advance, or indeed in any intermediate direction, 

 so that its possibilities as to variations of direction of locomotion are 

 reall}^ unlimited. 



But, other things being equal, is this a matter of indifference? 

 In certain echinoderms, e, g., holothurians and spatangoids, 

 there is a well defined antero-posterior differentiation with respect 

 to locomotion, accompanied, in most cases, by decided secondary 

 morphological bilaterality. It was in the attempt to throw 

 some light on these questions that the experiments reported in 

 this paper were undertaken. 



II. MATERIAL AND METHODS 



While it was hoped to test the matter not only with asteroids, 

 but with representatives of the other classes of Echinodermata 

 as well, the only animal with which more than tentative experi- 

 ments 'were accomplished was one of the common starfishes of 

 the New England coast, Asterias forbesi (Desor). The work 

 was begun at the United States Fisheries Laboratory^^ at Woods 

 Hole in the summer of 1909, and was continued later in the same 

 season at the Zoological Laboratory of the Sheffield Scientific 

 School of Yale University, at New Haven. 



As it was desired to determine the direction of locomotion 

 in the. absence of external stimuli of a directive nature, it became 

 necessary to make the conditions of the experiments as uniform 



^ I wish to express my indebtedness to Dr. Francis B. Summer, Director of 

 the Laboratory, and to the authorities of the United States Bureau of Fisheries 

 for the facilities of the laborator3\ 



