AUTHOR S ABSTRACT OP THIS PAPER ISSUED 

 BY THE BIBLIOGR.VPHIC SERVICE, DECEMBER 9 



REVERSION IN THE SENSE OF ORIENTATION TO 

 LIGHT IN THE COLONIAL FORMS, VOLVOX 

 GLOBATOR AND PANDORINA MORUM 



S. O. MAST 



Marine Biological Laboratory, Woods Hole, and the Zoological Laboratory of the 

 Johns Hopkins University 



TWO FIGURES 



CONTENTS 



Introduction 367 



Materials and methods 368 



Relation between illumination and reversion in orientation 369 



Relation between reversion in orientation and the quantity of light energy 375 

 Relation between reversion in orientation and the time rate of change in 



illumination 377 



Effect of the age of the colonies on reversion 378 



Effect of photosynthesis on reversion 379 



Effect of temperature on reversion 382 



Effect of chemicals on reversion 383 



Discussion 385 



Summary 388 



Literature cited 390 



INTRODUCTION 



The literature on reversion in the sense of orientation was 

 briefly reviewed in a preceding paper which dealt primarily with 

 the effect of chemicals on the sense of orientation to light in 

 Spondylomorum (Mast, 'LS). The results presented in that 

 paper indicate that reduction in alkalinity, increase in some anes- 

 thetics, increase in temperature and decrease in illumination all 

 have the same effect on the sense of orientation, causing photo- 

 negative specimens to become photopositive. They also indi- 

 cate that the same change in the sense of orientation may occur 

 without any appreciable change in the "environment. On the 

 basis of these results it was concluded that reversion in the sense 



367 



