1919] Esterly: Reactions of Various 'Plankton Animals 71 



(1916, pp. viii, ix, xi) to specificities in other respects than structure. 

 My study of the distribution of some of the Copepoda led to similar 

 views (Esterly, 1912, p. 328) and this matter has been more recently 

 discussed in papers on the experimental side (Esterly, 1917a, 1917c). 



Other writers have had this point of view as regards the behavior 

 of different organisms in the laboratory and also in nature. Walter 

 (1907) was aware of specific differences in Planaria. The same atti- 

 tude is apparent in the papers of Shelford (1911, 1912, 1914, 1915, and 

 especially 1916) and of Allee (1912, 1913) though those investigators 

 were primarily interested in other phases of behavior. It seems to me, 

 as has recently been pointed out by Patten (1917, p. 267), that the 

 attempt to arrive at blanket explanations is the main reason for the 

 controversy over the nature of the processes involved in orientation. 

 Such problems are primarily of physiological interest, and are there- 

 fore of a somewhat different nature than the problem of depth migra- 

 tion. But the general attitude of many investigators has been similar 

 in the two cases, especially as regards the failure to recognize that we 

 must deal with specific differences in behavior before a general law 

 can be determined, if such a thing is at all possible. We cannot tell 

 from studies conducted on a given kind of animal how another sort is 

 going to act. Jennings (1909, p. 315) writes: "The man who, from 

 a knowledge of how the starfish and sea anemone behave in the orienta- 

 tion to light, should attempt to predict how the infusoria behave under 

 the same conditions, would fail completely. More striking still, he who 

 from a knowledge of how Stentor becomes oriented in galvanotropism, 

 should predict how Stentor becomes oriented in phototropism, would 

 likewise fail completely. Different organisms respond in the same 

 tropisms by different methods of action. ..." And again: (p. 324) 

 ' ' Different organisms differ in their behavior and reactions just as they 

 do in their structure. ' ' If such statements are true as regards certain 

 matters in the physiology of behavior, they are doubtless equally true 

 as regards their relations between behavior in the laboratory and in 

 nature. 



If it is granted that a uniform and relatively simple explanation of 

 the depth migration of the plankton is possible, the first preliminary 

 step is to find out what each species does in nature. The facts about 

 migration can not be explained until they have been ascertained. Then 

 the study of reactions under controlled conditions should follow, and 

 this study should be carried on with different kinds of plankton 

 organisms. It is probable that sooner or later there will be duplications 

 in behavior of different species, so that similar explanations will apply. 



