12 LEON J. COLE 



an interesting relationship to the animal, for a line AA drawn 

 through arm e and the interradial area he divides the crawling 

 records almost equally into halves; 137 of the 499 records lie 

 on the line, while of the remaining 362 trials, 181.5 are on the 

 left and 180.5 on the right. Or if a line BB, at right angles 

 to AA be drawn through the center of the disc, 347 records 

 are in a direction 'ahead' of this line, while only 152 are 

 'behind' it.^ 



From the foregoing it may be concluded that, although the 

 starfish Asterias forbesi may move with any ray in advance, in 

 the absence of directive stimuli, as shown by ■ a large number of 

 trials, it was most often the one lying next to the left of the madre- 

 poric plate which went ahead. Using direction of movement as 

 a criterion, this may then perhaps be considered the 'physiologi- 

 cal anterior' of the animal. 



If we turn again now to the experiments of Jennings, it will 

 be recalled that in his study of the righting reactions he found 

 the ray e used most often, namely 89 times out of 95, "and the 

 next greatest numbers [werej shown by the two rays lying on 

 either side of e, namely a (56) and d (43)." His results are thus 

 directly comparable to those on the direction of movement, 

 and in each case a greater activity of the ray e and the rays 

 on either side of it is probably indicated. A somewhat similar 

 determination of direction of movement dependent upon a dif- 

 ferential activity of the organs of locomotion has been demon- 

 strated by the writer (Cole '01) in the pycnogonid, Anoplodactylus 

 lentus, in which the legs assume an essentially radial position, 



2. Relation of direction of locomotion to length of arm 



A possible explanation of the greater activity of the 'anterior' 

 rays (if we may so call them) is suggested by the observation 

 mentioned in the footnote on page 5 that in some of the speci- 

 mens used the arms b and c (the 'posterior' arms) were notice- 

 ably shorter. Unfortunately the actual specimens used in the 



° If the rays had been used indifferently, approximately 100 records would be 

 expected for each raJ^ 



