2 VICTOR E. SHELFORD AND W. C. ALLEE 



The senior author, for example, is able to distinguish some 

 species of tiger beetles (about one-half inch long) occurring near 

 Chicago, by their peculiarities of flight. Again, ornithologists 

 depend much upon characteristic movements to distinguish 

 species of birds. The details of action in the more stereotyped 

 reflexes of Protozoa and other of the lower invertebrates, such 

 as the backing and turning of Paramecium, are characters of 

 species or of groups of species. These specificities have been 

 much studied by some zoologists, but, like other specific char- 

 acters, serve chiefly as material for the study of modification, 

 and as characters to be used in cross breeding. 



The point of view of ecology is the one of most recent develop- 

 ment. It considers all phases of physiology that are related to 

 the life of the animals in their natural environments. The 

 behavior aspects which have been developed center around the 

 following questions: (1) Do animals select their habitats ? 

 (2) Is the behavior of the same species different under different 

 conditions ? (3) Is there community of behavior among ani- 

 mals of the same or similar habitats ? (4) To what factors of 

 the environment do animals respond and what is the degree of 

 the response to the different factors ? 



A relatively small number of investigations have answered the 

 first three questions in the affirmative, for the particular cases 

 studied. Studies on the effect of particular factors of the environ- 

 ment have been made, but usually with very small animals and 

 under conditions which made accurate measurement and control 

 of the experimental factors difficult. One of the most neglected 

 aspects of physiology and behavior is the reaction of larger ani- 

 mals to the different factors involved in the surrounding medium. 



From several points of view the importance of investigations 

 at this point seemed sufficient to more than justify an attempt 

 to determine whether or not fishes react to differences in the 

 dissolved content of the water which they inhabit and whether 

 or not different species differ in their reactions. The data 

 relating to these two questions have been organized and pub- 

 lished ( Shelf ord and Allee, '13). Apparent rapid modification 

 of the behavior of the fishes by repeated contact with the treated 

 water was quite characteristic of their reactions and aroused 

 interest sufficient to cause us to go over the results of one hundred 

 experiments from the point of view of modification. This in- 



