THE TWENTY-RAYED STARFISH. 



2O9 



have found them to be exactly as represented in my sketch (Fig. 

 3). I can not accept Ritter and Crocker's orientation represented 

 in their sketch (Fig. 2) ; but even if their interpretation should be 

 correct, and indeed it may be for young individuals, it docs not 

 hold for adults relative to their physiological anterior end. Rays 

 II., III., IV., V., I. represent the anterior end in respect to pro- 

 gressive movements of the starfish in its native environment (Fig. 

 3). The figure here is inverted, i.e., the madreporite should face 

 the reader on his left side ; the sketch is made from the inner side 



FIG. 6. Diagram of the asteroid groundplan of the metamorphosing com- 

 mon starfish. 1-5, radial vessels (larval); I-V, adult radial vessels; a, anus; 

 Lo, larval lobe organ; mp, madreporite. (From Ritter and Crocker.) 



of the aboral disk, looking down upon it. I am not concerned, at 

 this time, about the controversy I may be led into relative to the 

 difference between Ritter and Crocker's diagram and their inter- 

 pretation and my diagram ; I am only recording facts relative to 

 the physiological anterior end in Pycnopodia helianthoides (Stimp- 

 son), and I am trying to adjust myself as far as possible with the 

 accepted view in this field of morphology. In my opinion, the 

 apical radial muscles of Pycnopodia, relative to their axial arrange- 

 ment to the physiological anterior and posterior ends, fit in very 

 well with the marked bilaterality of the adult, as I have recorded 



