PROCEEDINGS 



OF THB 



WASHINGTON ACADEMY OF SCIENCES 



Vol. II, pp. 247-274. October 10, 1900. 



PAPERS FROM THE HARRIMAN ALASKA 

 EXPEDITION. 



III. 



MULTIPLICATION OF RAYS AND BILATERAL 

 SYMMETRY IN THE 20-RAYED STAR-FISH, 

 PTCNOPODIA HELIANTHOIDES (STIMPSON). 



By Wm. E. Ritter and Gulielma R. Crocker. 

 [Pis. XIII and XIV, figs. 1-13.] 



CONTENTS : 



Introduction, by W. E. Ritter 247 



Lack of knowledge regarding production of accessory rays 24S 



General remarks on characters and orientation 250 



General account of ray multiplication 252 



Diflferences between primary and secondary rays 253 



Origin and growth of new rays 255 



Questions and Conclusions 260 



Bibliography 269 



INTRODUCTION. 



Having had the good fortune to spend the early summer of 

 1899 in Alaska, as a member of the scientific staff of the Harri- 

 man Alaska Expedition, I was able to collect a fine series of the 

 Pacific coast star-fish {Pycno^odia helianthoides) which follows 

 the coast northward from central California to southeastern 

 Alaska. At Yakutat Bay, near the northern limit of its range, 

 I found it about the middle of June in greater abundance than 

 I have ever seen it elsewhere. 



Proc. "Wash. Acad. Sci., October, 1900. ( 247 ) 



