WATER RELATIONS IN HIBERNATION. 25 I 



hibernation, and further since these states are known in experi- 

 ments to be alternative in hereditary behavior, one must not be 

 too fast nor certain in arriving at conclusions in these complicated 

 physiological activities. 



Regardless of what one may believe concerning the alteration 

 or the findings of subsequent investigations, certain aspects of 

 its nature are demonstrated, its sharp alternativeness in heredity, 

 its role in the determination of survival in different habitats, its 

 directly adaptive nature; and its alteration in direct response 

 to the conditions of the medium in adaptation to those conditions; 

 these aspects of its nature show an alteration, a character capable 

 of alteration, in ways that are of importance in the survival of 

 the organisms, and that might be of decided value in evolutionary 

 activities, speciation, and in ecological and distributional rela- 

 tions and results. 



METHOD OF ORIGIN. 



This account deals with experiments that are concerned with 

 populations, and the results seem to be those of the alteration 

 of the population as a whole. As shown, the experimental 

 method was such that as far as the operator was aware, the 

 choice of materials was random and entirely impersonal, and 

 throughout any personal influence has been eliminated as far 

 as known. Further, the living of the cultures in cages eliminated 

 the action, if any, of enemies and further gave the cultures 

 better conditions of life than they would have had in nature. 

 Insofar as is known, therefore, the series deals with the response 

 of an introduced population to the physical conditions of its 

 environment. What are the methods of origin of this response 

 and alteration? There are several possibilities: 



i. That the original population consists of different pure lines, 

 which under the conditions of the original habitat interbreed, 

 and. are hidden from recognition, but that under the Tucson 

 conditions one has been able to survive with the characteristics 

 found, and that the progressive development of its full intensity 

 is the gradual elimination under the conditions of the experiment, 

 of all but the one line with the characteristics finally developed. 

 The conditions of experiment are, therefore, acting only as a 

 sieve to separate out those capable of survival from those not 



