382 University of California Publications in Zoology [^'ol. 16 



that the primary object of all studj^ of living tilings is to further our 

 knowledge of them as they exist in nature. An organism is first of 

 all something in nature, and its natural history must be known if 

 we are studying nature and not merely objects in a laboratory. The 

 far-reaching importance of natural history is well presented by 

 Jordan (1916), and the "natural history" method is evidently the 

 one Jennings has called analj'tic. 



Both the synthetic and analytic methods are necessary and 

 valuable means of getting information, and the method to be used 

 depends on what the investigator wants to do. My work for the last 

 half-year has been the study of the responses of as many different 

 plankton organisms as possible, with a view to applying the results 

 to the habit of diurnal depth migration. As I regard it, this requires 

 the analytic method, and my position as to the relation between 

 experiment and field observation coincides with that more fully pre- 

 sented by Michael (1916, p. xi), and so well emphasized by Hargitt 

 (1912, p. 51). 



Certain considerations have appeared with special bearing on this 

 particular problem; but they also have important significance in any 

 investigation intended to fiirnish some of the reasons for habits in 

 nature. It is the more general application of my results that I wish 

 to point out, rather than their meaning for the immediate problem. 



The relation between the reactions of plankton organisms and the 

 habit of periodic vertical migration has received much attention 

 (Groom and Loeb, 1890; Parker, 1902; Loeb, 1908, 1913; Dice, 1914). 

 Such migration in nature is abundantl.y established by field obser- 

 vations. The reasons for the movement, however, will apparently 

 come from studying reactions. But, whatever the explanation of 

 the movement may be, there are certain matters involved in the 

 experimental side that will inevitably affect the results of the tests. 

 Habit will therefore be wrongly interpreted in the light of experiment, 

 unless these modifying factors are considered. 



The discussion that follows deals with three such factors. 



1. Generic and Specitic Differences in Behavior 

 The most general result, probably, of a prolonged study of the 

 collecting records of the Scripps Institution is the outstanding fact 

 that each kind of organism has its own habit, particularity as regards 

 the vertical migration. Michael (1916, p. xiv) has referred to this, 

 and his paper dealing with the chaetognaths (1916) gives further 



