AUTHOR S ABSTRACT OF THIS PAPER ISSUED 

 BY THE BIBLIOGRAPHIC SERVICE, AUGUST 5 



REACTIONS TO LIGHT IN THE LARVAE OF THE 

 ASCIDIANS, AMAROUCIUM CONSTELLATUM AND 

 AM.AROUCIUM PELLUCIDUM WITH SPECIAL REF- 

 ERENCE TO PHOTIC ORIENTATION^ 



S. O. MAST 

 Zoological Laboratory, The Johns Hopkins University 



TEN FIGURES 



CONTENTS 



Introduction 149 



Material and general behavior 150 



Nature of response to decrease in illumination 154 



a. Resting specimens 154 



b. Active specimens 162 



Reactions to increase in illumination 164 



Function of the eye 172 



Photic orientation 177 



Wave-length and stimulation 182 



Discussion 182 



Summary 185 



Literature cited 187 



INTRODUCTION 



It is well known that the larvae of many aquatic animals 

 respond to light and it is generally assumed that their response 

 facilitates distribution. There is, however, practically nothing 

 known regarding the precise nature of these responses. 



1 I am indebted to the Marine Biological Laboratory of Woods Hole, Massa- 

 chusetts, for working facilities and to .Dr. Caswell Grave for calling my attention 

 to the photic responses of the ascidian larvae and very generously supplying me 

 with some of his material. Doctor Grave has made a very thorough study of the 

 structure and habits of the larvae of the two species used in this work, and the 

 descriptions in this paper, in so far as they refer to structure and habits, are 

 based very largely upon his work, some of which is published (Grave, '20), some 

 in press, and some in the process of preparation for publication. 



149 



