WATER RELATIONS IN HIBERNATION. 253 



Further in the elimination incident to hibernation, that found 

 in preparation for hibernation remains about a constant per- 

 centage (about n) throughout the series at Chicago and Tucson, 

 the difference in the two is in the elimination that takes place 

 during hibernation. The introduced populations at Tucson were 

 all of individuals that had survived the Chicago winter's hiberna- 

 tion, whereas the materials returned to Tucson for testing did 

 not survive the Chicago winter, as shown in the records of the 

 tests. 



There is, therefore, no evidence nor reason to interpret the 

 results of the experiments as being due to the isolation at Tucson 

 of pure lines from the introduced population, and every reason, 

 as shown above, why this interpretation is highly improbable. 

 The pure line concept is so facile and insidious in its possi- 

 bilities for interpretation, that the result of the series of experi- 

 ments are easily interpreted to conform therewith. 



Since 1910 I have tried to develop pure lines from the materials 

 at Chicago with respect to this water retention, and have not 

 up to the present the least evidence that such exist, nor has the 

 slightest success attended my efforts along that line. I cannot 

 go beyond the facts of experience and must, therefore, conclude 

 that upon the basis of the evidence available, pure lines of the 

 characters developed in the Tucson experiments do not exist 

 in the parental materials, and that the results are not due to 

 the sieve-like action of the Tucson environment upon the intro- 

 duced population, and I believe that this conclusion is entirely 

 justified upon the basis of facts at present available. 



It may be assumed that the condition developed was in cor- 

 relation with some other characteristic operative at breeding, 

 and that introduction eliminated those not possessed of this 

 trait, but in these introductions, as in the T 99 series, from 

 actual observation the entire introduced population took part in 

 the initial breeding, and nowhere have I found the least indica- 

 tion that there has been any such relation, although I have been 

 upon the lookout for them. 



That the results are the product of the selection of favorable 

 or adapted variations surviving from among multifarious varia- 

 tions, regardless of size, a product of natural selection, is without 



