CHAP. XVII.] 



ASTEROIDEA. 



439 



ASTEROIDEA. 



670. Symmetrical change in number of rays is common in some 

 of the forms. Asterias rubens and A. glacialis are frequently 

 seen with 6 or with 7 arms symmetrically arranged, and I have 



anus 



FIG. 133. Antcdon rosacea having two arms abnormally divided. The figure A 

 shews the relations of the two abnormal arms, & and t'j, to the mouth and anus. B 

 shews the arm b. 2 . (From Proc. Zool. Soc.) 



