280 The Unity of the Organism 



vestigations have dealt with, so a reader interested in the 

 question of specificity can usually detect evidences of dif- 

 ferences in the behavior of different species, even though the 

 investigator himself was obviously little interested in the 

 subject, and so took no pains to bring out such evidence. 



Indeed, the fact that species-differences in behavior can so 

 frequently be recognized in descriptions even though the 

 writer's general attitude may, if anything, militate against 

 the disclosure of the differences, is rather strong evidence 

 of the general prevalence of such differences. 



(3) Although statistical investigation of animal behavior 

 has been much less prosecuted than has either of the other 

 types it is, nevertheless, within the limits of its availability, 

 a very valuable method for revealing species differentia, its 

 efficacy consisting in the fact that species may be compared 

 with reference to different behavior traits taken one by one, 

 and on the basis of quantitative data covering considerable 

 samples of whole populations. The method is specially ap- 

 plicable to the minute floating life of the seas and lakes, 

 known as plankton, and is being much employed to this end 

 at the Scripps Institution for Biological Research. It can- 

 not be described in detail here, but consists essentially, as 

 employed at this Institution, in collecting great quantities 

 of organisms by agencies as nearly quantitatively constant 

 and accurate as possible, in counting the organisms thus 

 secured, and in correlating the biological values thus ob- 

 tained with quantitative studies on the physical environment 

 of the organisms, these environmental determinations being 

 made simultaneously with the collection of the organisms. 

 By this means one element in the behavior, that namely of 

 the up-and-down journeys in the sea, long known to be per- 

 formed by many oceanic species, has been studied with a fair 

 degree of quantitative accuracy as to the extent of travel, 

 time required for each journey, and environmental influence. 

 A considerable series of species have been compared on this 

 basis. 



