OBSERVATIONS ON THE BEHAVIOR OF THE 



HOLOTHURIAN, THYONE BRIAREUS 



(LESEURV 



A. S. PEARSE. 



PAGE 



I. Introduction 259 



II. Structural Characteristics 260 



III. Metliods of Response to Stimuli 263 



IV. Locomotion 264 



1. On a Solid Surface 264 



2. Burrowing 266 



V. Feeding 268 



VI. Respiratory Movements 271 



VII. Responses to Stimulation 273 



1. Tactile Stimulation 273 



2. Gravity 273 



3. Chemical Stimulation 275 



4. Change in Density of Surrounding Medium 276 



5. Light Stimulation 277 



6. Thermic Stimulation 279 



VIII. Experiments to Determine whether the Integrity of the Nervous System 



is Essential to Reactions 281 



IX. Variability of Reactions 283 



1. Effect of Repetition of Stimulus 284 



2. Inhibition 285 



• X. General Considerations 286 



XI. Bibliography 288 



I. Introduction. 

 The different classes of echinoderms show in a remarkable 

 way the extreme variations which one fundamental plan of 

 structure may undergo in order to become adapted to different 

 conditions of existence. Developing from a bilaterally sym- 

 metrical pelagic larva, the adult echinoderm becomes an almost, 

 perfect type of radiate symmetry, except in those forms which 

 have a bilaterality superposed secondarily upon the typical radi- 

 ate plan of structure, so that the adult becomes bilaterally sym- 

 metrical only after it has passed through the more primitive 



'Contributions from the Zoological Laboratory of the University of Michigan, No. 

 119. 



259 



