THE TWENTY-RAYED STARFISH. 



20 5 



'' Before Ludwig was consulted, this orientation had been adopted 

 for Pycnopodia, owing to the striking bilateral symmetry displayed 

 in the young animals. This symmetry determined that the sixth 

 ray is median anterior between I. and II., and by us has been called 

 "A" (Figs. 4, 5). Ritter and Crocker's diagram (Figs. 4 and 5) 

 agree with Ludwig's (Fig. i). The relative position of ray "A," 



FIG. 3. A diagram of the dorsal radial muscles of Pyncnopodia lielian- 

 thoides to show the relation of the primary and secondary rays to the physio- 

 logical anterior end. (Rays I, l.r fl , /.r-,, /.r 4 , /.i' 3 , correspond to I, V, IV, III, II 

 (Fig. 2) respectively) ; rays I-V, rays of the physiological anterior end; these 

 rays, and ray A, are, perhaps, the primary rays ; rays l.v-lx r ,, the secondary rays 

 of the left side; rx-rx^, the secondary rays of the right side correspondingly; 

 rays rx s , and /.r,,, the youngest rays, a, anus ; Mp, madreporic plate. This 

 sketch is made from the under side of the dorsal muscles. 



in Pycnopodia, according to Ritter and Crocker, to the five rays of 

 the asteroid ground plan, is between the left and right anterior 

 rays (Figs, i, I.-IL; and 4, I.-II.) ; the axis of bilateral sym- 

 metry, or Ludwig's orientation line, lies along rays A IV. (Fig. 



