68 University of California Publications in Zoology [Vol.19 



reasonably be expected that the reactions of surface animals will be 

 different from those of specimens from deep collections. 



The behavior Acartia tonsa shows clearly how different the behavior 

 of surface and deep water animals can be. This matter has been dealt 

 with before (Esterly, 1917a, and also in this paper), but it is worth 

 emphasizing again. This copepod is positive to light and negative to 

 gravity in the light and positively geotropie in the dark, providing the 

 specimens come from the surface. But animals that are obtained in 

 deeper water (10-20 fathoms) are negatively phototropic and posi- 

 tively geotropie soon after capture both in diffuse light and in dark- 

 ness. In this case, furthermore, there is a marked change in the 

 behavior of specimens from deep water after they have been in the 

 laboratory, for they come to react in all respects as do the animals 

 from the surface. 



I have not had the opportunity to compare the reactions of speci- 

 mens from the surface and low levels of other forms than Acartia. 

 It seems to me, however, that the results with that species are sug- 

 gestive of possibilities in other forms. They show that the physio- 

 logical state really is different, depending on the habitat from which 

 the experimental specimens are obtained. What is true of one species 

 is not necessarily true of another, but it is difficult to avoid the con- 

 clusion that the effect of laboratory conditions must be considered. 

 At any rate an observer should look for the evidences of change in 

 physiological state that may be connected merely with confinement in 

 the laboratory before he uses experimental results to explain habits 

 in nature. 



Specificity in Behavior 



Diurnal migration is a complex natural phenomenon in which 

 many different kinds of organisms take part. The cause of the migra- 

 tion in each species is a particular problem, and there is need to realize 

 that the facts of behavior of one form may not apply to others. A gen- 

 eral explanation of the movement is desirable, of course, and the 

 matter may be approached from the experimental side with a working 

 hypothesis in mind. But a 'blanket explanation' will lead to con- 

 troversy unless it is based upon experimental results obtained from a 

 wide range of organisms. It is necessary to work first on specific 

 problems since the phenomena recorded and the animals studied are 

 so varied. An explanation based on the results of experiments with 

 one sort of copepod can not be assumed to be applicable to another or 



