336 VICTOR E. SHELFORD. 



longing to a single species, or of communities composed of all 

 the animals of a locality without regard to their taxonomic 

 relations, is based upon differences and similarities of mores or 

 general physiological characters. These differences in mores are 

 measured (a) by the direct study of the organism, and (6) by the 

 study of the environment of the organism or the mould into which 

 the organism fits. As a background for our point of view, we 

 have, under the first heading, various experimental studies of 

 adjustment of the behavior of organisms to surrounding condi- 

 tions, especially studies of the modifiability of behavior, which 

 has been definitely related to conditions which the organisms con- 

 cerned encounter in their normal life in nature; under the second 

 studies of the selection of habitat by organisms. My own studies 

 (Shelford, 'n 3 ) from this point of view are at present very in- 

 complete and serve to illustrate the methods only. Different 

 tiger beetle species select different soils and as the females lay 

 only one season, their first attempts at laying no doubt are the 

 result of innate behavior (Shelford, '07). The work of many 

 investigators (Wheeler, '10, et al.) confirms the general view 

 that animals select their habitats upon the basis of characters 

 more or less innate. The work of naturalists is important though 

 it is defective mainly in that one often has difficulty in deter- 

 mining what habitat is meant. 



A type of investigation which combines experimental and 

 naturalistic consideration of the organism with analysis of the 

 environment has been carried on by Alice ('12). He found that 

 the rheotaxis of isopods of the same species occurring in both 

 ponds and streams, is different in the two situations. He was 

 able to change the pond mores to the stream mores by keeping 

 pond isopods in stream conditions and vice versa. The agree- 

 ment of the behavior of the animals of a habitat will be shown 

 by a study of the behavior of the swift brook community now 

 being conducted. There is a marked agreement of the animals 

 of this community in their reactions to the factors encountered in 

 the stream. This agreement is due (a) to the selection of the 

 habitat through innate behavior, and (b) to the adjustment of 

 behavior to the conditions through the effects of physical factors 

 and through formation of habits and associations. 



