1919] Esterly: Reactions of Various Plankton Animals 79 



GENERAL CONCLUSIONS 



The results of the experiments have led to the following conclu- 

 sions of general application : 



1. Owing to specific differences in behavior no general explanation 

 of diurnal migration can be given at present. It is suggested by the 

 experiments that each kind of organism will have its own way, so to 

 speak, of performing the vertical movement, as each has its own 

 peculiar responses in the laboratory. 



2. There is evidence that the physiological state changes when the 

 animals are removed from the ocean and kept in the laboratory. While 

 this has not been noted for each species, it is necessary to guard against 

 errors in interpretation that may arise through that cause. We should 

 inquire whether reactions under controlled conditions in a glass vessel 

 are similar in kind to those that would be observed if it were possible 

 to have the element of control and at the same time retain the animals 

 under otherwise natural surroundings. 



3. It is suggested by some of the experiments that behavior is in 

 some way related to the habitat from which the experimental speci- 

 mens are obtained. In general it seems highly desirable to use both 

 animals that are obtained in deep water and at the surface, and com- 

 pare the reactions in the two cases. If this is not done the possibility 

 remains that what is learned about habit from reactions in the labora- 

 tory is not characteristic of the species as a whole, but only of the 

 particular specimens tested. 



4. Field studies and laboratory investigation are both necessary 

 and supplementary to each other. While studies on reaction possi- 

 bilities do not require that the natural habits of the animals be known, 

 this knowledge is a necessity when responses are studied in the expec- 

 tation that they will reveal the reasons for a habit in nature. 



5. So far as these experiments go (they are incomplete in many 

 respects) there is apparently no adequate explanation of diurnal mi- 

 gration that can be based on responses to external stimuli except in 

 the case of Sagitta. Additional information may make possible the 

 explanations desired for the other species. It appears, however, that 

 change in geotropism with change of light intensity or in temperature 

 is not general enough to be considered as of wide significance. 



6. The action of what may be called a physiological rhythm is 

 clearly shown under certain conditions by the two species of Acartia. 



