DIRECTION OF LOCOMOTION OF THE STARFISH 



15 



As noted above, however, the axis which marks the approach 

 to bilateraUty in these determinations {A A, fig. 7) does not accord 

 exactly with that with respect to direction of locomotion {AA, 

 fig. 5); for whereas in that case it passed through arm e and 

 between arms b and c, here it obviously passes through arm a 

 and the interradius cd. 



(46.30) ^^ \^ (46.74) 



25 4, 



40 28 



Fig. 7 Diagram of starfish, showing number of individuals in 116 specimens 

 in which a particular arm was longest or one of the two longest (black face fig- 

 ures) and in which it was shortest or one of the two shortest (italic figures). Com- 

 pare with figure 6. Figures in parentheses are the mean lengths in millimeters 

 of the respective arms of the 110 specimens as determined. AA, line of sym- 

 metry with respect to these figures. 



Considering the considerable amount but irregular distribu- 

 tion of the variation in arm length and the very small difference 

 in mean length of the different arms, as well as the difference 



marked difference in arm length of a given individual, the mean arm lengths of 

 the 116 specimens should be practically equal. The greater individual varia- 

 tion gives somewhat greater value to the tabulation on p. 13 of the number of 

 times a particular arm occurred as the longest or shortest than to the mean lengths. 

 But even if these figures could be relied upon the fact would still need to be con- 

 sidered that they do not refer to the actual specimens used in the experiments. 



