DIRECTION OF LOCOMOTION OF THE STARFISH 23 



any other in righting themselves; in the present experiments it 

 was found that Asterias forbesi moves more often with ray e 

 in advance than with any other. Furthermore it was found in 

 the comparative!}' few experiments which were made with respect 

 to righting that the East Coast starfish also used rays e and a 

 most frequently for this purpose, but these individuals, in the 

 great majority of cases, then crawled with the opposite rays in 

 advance. Which, way would Jennings' starfish have crawled? 



V. COMPARISON WITH OTHER ECHINODERMS 



It would be interesting to know whether the tendency for a 

 predominance of movement to be with a particular region of the 

 body forward obtains in other starfishes and in the other groups 

 of (practically) radial echinoderms. The statement is not un- 

 commonly made categorically bj^ authors, based only on general 

 observations, that no preference is shown for a particular ray or 

 region. Thus Cowles states in a preliminary report ('09, p. 

 128): ''Echinaster in locomotion does not show any tendency 

 to use a special ray, or pair of rays, as directors." He admits 

 later, however, that although this conclusion was ''based on a 

 considerable number of observations with directive light ex- 

 cluded," it was ''not a careful statistical study" (Cowles '11, 

 p. 98). Grave ('00, p. 86) remarks similarly: "No preference 

 as to which arm should precede could be found in an adult ophi- 

 uran, each arm being equally capable of going before, making 

 the stroke, or following behind." But while each arm might 

 be 'equally capable' of performing these actions, it does not fol- 

 low that they would be used equally for that purpose. Bohn 

 ('08, p. 29) says regarding the relative value of the arms in 

 Asterias rubens that commonly they are the same functionally, 

 but if any are shorter or are mutilated they have a relatively 

 smaller value. Further on in the same paper (p. 43) he asserts 

 that the small specimens of this species (rays 1 cm. in length), 

 which are found on the Zostrea, and which are very active and 

 in general show a positive phototropism, use all their arms with 

 practical indifference. Larger specimens, however, sometimes 



