260 VICTOR E, SHELFORD AND W. C. ALLEE 



connection with the breeding period and breeding condition, if we 

 are to explain the distribution of fishes in nature and make our 

 groupings ecological. The number of ecological factors is clearly 

 great. The entire life history of the species must be studied 

 both by experiment and by observation and first, as we believe, 

 with particular reference to the physiological characters of the 

 greater inagnitude, leaving the specific aspects until later. For 

 these reasons we have studied several species, hoping to get a 

 hint concerning these physiological characters of the higher order. 

 That is, we were hunting for the generalities of behavior that 

 would apply to ten species of fishes widely distributed taxo- 

 nomically, rather than the specific details of the behavior of 

 any one species. Had we chosen to work entirely on Abramis, 

 the abundant and easy species, we could have completed a 

 detailed bit of work of a type highly approved by investigators 

 but which would clearly have led us into error, because of the 

 specific peculiarities of the species. These peculiarities would 

 have led to incorrect interpretations of the behavior of the indi- 

 vidual fish and to a much greater error if the data had been used 

 as a basis for generalizations. Thus we would have accumulated 

 a mass of details of doubtful application to current problems, 

 however interesting they might have been of themselves. Had 

 we studied only darters we should have erred in a still more 

 dangerous direction. 



Turning to the practical appHcation of our conclusions to 

 current biological problems, we find that they fall under three 

 main heads. First, the economic and distribution problems; sec- 

 ond, the problems of fish physiology; and third, the problems of 

 behavior and psychology. From the economic point of view, it 

 appears to us from these experiments, that emphasis has b€;en 

 wrongly placed upon environmental factors as matters of life 

 and death to the fishes concerned. Clearly, fishes are often 

 absent from accessible situations which upon inspection appear 

 favorable, and where an examination of the water shows condi- 

 tions entirely compatible with life. It appears also that the 

 importance of oxygen in determining the distribution of fish, has 

 been too much emphasized. The oxygen optimum of all the 



