30 LEON J. COLE 



The third suggestion is that the observed facts regarding 

 locomotion may be explained by some peculiarity of the nervous 

 or water vascular systems. As to the former of these, the ner- 

 vous system appears to offer no peculiarity which could account 

 for a differential in the locomotion. On the other hand, in the 

 water vascular system we do find a special structure which 

 breaks up the radial syimnetry and which bears a positional 

 relationship to the physiological differentiation observed in the 

 locomotion. This structure is the madreporite, which connects 

 the water vascular .system with the exterior. 



It will be recalled that whereas the experimental results esta- 

 lished for Asterias forbesi a plane of physiological bilaterality 

 through arm e and between h and c (cf. fig. 5), arm a was found 

 to be most frequently the longest or one of the two longest (fig. 

 6 and table, p. 13), and also had the greatest mean length. 

 These facts were shown in figure 7, which shows the axis passing 

 through arm a and between arms c and d. Preyer's experi- 

 ments on other starfishes, on the other hand, indicated a plane 

 passing between e and a (thus intersecting the madreporite) 

 and through arm c (p. 26). The significant fact appears to 

 be that all these data seem to indicate a plane passing through 

 or near the madreporic plate. Proximity to the madreporite 

 seems then to be associated in some way with a greater activity 

 or other functional superiority of the tube feet on the arms so 

 situated, for such is probably the reason for the preponderance 

 of locomotion in this direction. Just why this should be so is 

 not so clear, though it may be purely mechanical; this portion 

 of the ambulacral system may be able to adjust itself more read- 

 ily to changes in volume of contained water, consequent upon 

 the activity of the ampullae and tube feet, because of its near- 

 ness to the outside reserve, that is, the outside water surrounding 

 the starfish, just as a better supply is had near the mains of any 

 water system than in the more remote branches. ^^ 



" It would be interesting to determine whether there is possibly a difference 

 in caliber of the radial tubes in different arms, and whether this is related 

 to their nearness in origin to the stone canal. 



