BILATERAL TENDENCIES AND HABITS IN THE 



TWENTY-RAYED STARFISH PYCNOPODIA 



HELIENTHOIDES (STIMPSON). 



H. P. KJERSKOG AGERSBORG, 



DEPARTMENT OF BIOLOGY, THE COLLEGE OF THE CITY OF NEW YORK, 



DEPARTMENT OF ANATOMY, LONG ISLAND COLLEGE HOSPITAL, 



BROOKLYN, N. Y. 



CONTENTS. 



A. Introduction 232 



B. Ecology: 



I. Distribution 233 



II. Movements: 



1. Righting Reactions 234 



2. Tidal Movements 240 



3. Migratory Movements 244 



(a) Reaction toward Light 244 



(b) Search for Food 246 



(c) Breeding Impulse 246 



III. Feeding- 



1 . Kinds of Food 247 



2. Methods of Feeding 247 



IV. Conclusions on Movements in General 249 



V. Meristic Variation 249 



C. Summary 251 



D. Bibliography 252 



INTRODUCTION. 



The purpose of the investigation upon which this paper is 

 based is to show to what extent the radial symmetry in Pycno- 

 podia helienthoides is disturbed by its bilateral tendencies. 



The nature of the investigation has been primarily based on 

 observations on the animal in its native home, and as little as 

 possible have conditions been introduced during experimentations 

 which would deviate from that of it > natural abode. 



The carrying out of this experimental work on Pycnopodia 

 was done in connection with other work at the University of 

 Washington, during the year 1915, and during part of the summer 

 of 1916. The experimental work was done at Bremerton, Wash., 

 w r hich is situated about twelve miles from Seattle. In some of 



232 



