2 University of California Publications in Zoology [Vol.19 



PAGE 



Reactions of the chaetognath Sagitta bipunctata 54 



Phototropism .is 



Geotropism 58 



Summary 62 



Possible bearing of the experiments on diurnal migration 64 



General discussion 66 



Effects of laboratory conditions in general on experimental animals 66 



Specificity in behavior. 68 



Phototropism ....... 60 



Geotropism . 69 



Relation between geotropism and diurnal migrations 72 



Does getropism change as intensity of light varies? 73 



Does geotropism change as direction of light varies? 73 



Does geotropism in diffuse light and in darkness change with alterations 



of temperature and salinity?. 74 



Does the direction of vertical movement in directive light change as the 



temperature changes? 74 



To what extent will behavior under recurrent external conditions explain 



diurnal migration?.. 75 



The relation between experimental and field work 77 



General conclusions... 79 



Bibliography 81 



INTRODUCTION 



This paper reports the results of a year of study on the behavior of 

 some marine plankton organisms. The chief aim of the work was to 

 ascertain the factors that determine the diurnal migrations of such 

 forms. It was outside my purpose to attempt to learn how sensitive 

 the animals under experiment might be toward changes in surround- 

 ing factors such as light or temperature, for example. It was not in 

 the plan, furthermore, to consider questions connected with the inter- 

 pretation of behavior as applied to such matters as the mechanism of 

 orientation. The end desired was to learn how the direction of move- 

 ment is affected by various external conditions. The actual experi- 

 mental facts were sought rather than the laws or principles under- 

 lying them. Since the experimental work was not concerned with the 

 physiology of the movements controversial matters connected with that 

 phase of the study of behavior are not discussed. 



It is important that it be understood that this investigation of 

 responses was undertaken with the definite end in view of obtaining a 

 basis for explaining habits in nature. The natural conditions experi- 

 enced by the animals in the course of the vertical movement were 

 constantly considered, and the mode of procedure was based on that 

 consideration. In general, it may be said that during descent the 

 temperatures encountered are progressively lower, and during ascent 



