THE GEOTROPISM OF THE SEA-URCHIN CENTRECHINUS. 375 



locomotion are really unlimited." Cole (1913) in his study of the 

 New England starfish, Astcrias forbcsi, demonstrated in this spe- 

 cies the same unlimited possibility of direction of locomotion that 

 Jennings had done for A. forrcri, but Cole further showed by 

 means of statistical methods that A. forbcsi moved more fre- 

 quently with that part forward which was in close proximity to 

 the madreporite than with any other part. He, therefore, estab- 

 lished what has been called a physiological anterior for this species, 

 an anterior that corresponds almost exactly with that assumed on 

 different grounds by Loven for echinoderms in general. Cole's 

 observations form, as a matter of fact, a rather remarkable con- 

 firmation of Loven's deductions. 



Agersborg (1918, p. 233) in his study of the habits of the 

 twenty-rayed starfish of the Pacific coast, Pycnopodia hclian- 

 tlioidcs, calls attention to its bilateral tendencies and states that it 

 does not readily move backward or sidewise, but uses the side 

 established as fore end always as anterior end. He, however, 

 nowhere makes really clear how its physiological bilaterality is 

 related to its structural bilaterality. If they agree, as his account 

 seems to imply, then the physiological anterior of Pycnopodia must 

 be different from that of Astcrias, judging from the account of 

 the structure of Pycnopodia given by Ritter and Crocker (1900). 

 In Astcrias, according to Cole, the physiological anterior centers 

 on the arm to the left of the madreporite as viewed aborally (III. 

 in Loven's system). In Pycnopodia it appears to center on the 

 second arm to the right from the madreporite as viewed aborally. 

 Thus the axis of locomotion in Astcrias is two fifths of a circum- 

 ference from that in Pycnopodia. But this conclusion is based on 

 statements of structure from Ritter and Crocker and of habits from 

 Agersborg, both of which may be open to fundamental revision. 

 So far as Pycnopodia is concerned, the one thing that in reality 

 seems certain is that it has a physiological anterior, but how this 

 is related to its structure remains to be ascertained. 1 



The Bermudian starfish, Coscinasterias tenuispina, has been 

 studied in its methods of reproduction and of locomotion by 

 Crozier (19200-). This species propagates by division and conse- 



i This subject is not greatly clarified in a second paper recently published 

 by Agersborg (BiOL. BULL., vol. 42, p. 202). 



