The Journal of 



Comparative Neurology and Psychology 



Volume XVIII JUNE, 1908 Number 3 



THE BEHAVIOR OF THE LARVAL AND ADOLESCENT 

 STAGES OF THE AMERICAN LOBSTER (HOMARUS 

 AMERICANUS).^ 



BY 



PHILIP B. HADLEY. 



{From the Biological Laboratory of Brown University and the Experiment Station of the Rhode Island 

 Commission oj Inland Fisheries.) 



With Twenty-two Figures. 



OUTLINE OF CONTENTS. 



I. Introduction and historical summary 200 



II. Biology of the lobster 203 



III. Apparatus and method of procedure 2.05 



IV. Preliminary experiments 208 



V. Systematic account OF THE REACTIONS to light of lobsters in the larval stages . . 216 



1 . First larval stage ; 217 



2. Second larval stage 228 



3. Third larval stage 232 



4. Fourth stage 241 



5. Fifth stage 248 



A. Photopathy versus phototaxis 250 



B. Phototaxis leading to fatal results 251 



C. Conclusions concerning the reactions to light of fiffh-stage lobsters 253 



D. Contact-irritability versus reaction to light 253 



VI. Mechanics of orientation 258 



1. The normal behavior of the lar\'ae 258 



2. Mechanics of progressive orientation 261 



3. Mechanics of body-orientation 263 



A. The effect of direct lighting and shading 264 



B. The effect of screens and backgrounds 277 



VII. Analysis 289 



VIII. Summary 298 



IX. List of references 3°° 



1 The present paper is the last of the series of four in which the author has attempted to analyze the 

 behavior of the larval and early adolescent stages of the lobster. The papers already published are the 

 following, references to which may be found in the bibliography at the end of the present work: (i) 

 The relation of optica! stimuli to rheotaxis in the American lobster; (2) Galvanotaxis in larvae of the 

 American lobster; (3) The reaction of blinded lobsters to light. 



