254 WILLIAM LAWRENCE TOWER. 



any confirmation. The chief change takes place between intro- 

 duction and the first period of hibernation in the elimination 

 during hibernation, and there is therefore no opportunity for the 

 operation of such selective action, even though it is present in 

 the following two or three hibernations. I have tried to devise 

 tests of this point, thus far without any success, and rather 

 extensive breeding of pedigree pairs from these cultures have 

 thus far given only negative results in this line. While I admit 

 its possibility and its value as a basis for argument or inter- 

 pretation, I am still without any evidences at all that can be 

 used either way concerning this possibility, and am of the opinion 

 that it is not, in view of the findings, a plausible interpretation 

 of the results. 



Concerning the possibilities of the reactivation of latent 

 agents, under the conditions of experiment, a plausible inter- 

 pretation could be made, if the initial assumption is made 

 that such latent agents exist, an assumption that might receive 

 some support from the probable phylogenetic history of these 

 animals. Were any such condition latent in these beetles, it 

 would seem that some indication would have been found of it in 

 the rather extensive experiments that have been in progress in 

 the last ten years, especially those that have to do with the 

 reproductive cycle and hibernation; but as far as I am aware, 

 there has been no indication thereof, and finding of it would 

 have been of considerable value in many of my experiments, and 

 after all the finding of the latency would not in this instance be 

 of much service in the interpretation of the results. 



It seems to me that the most plausible interpretation of the 

 results of these experiments is that we are dealing with a case 

 of the response of the entire introduced population, of uniform 

 composition and behavior, in a determinate variation in Darwin's 

 sense. A population reaction to the conditions of a new en- 

 vironment in a characteiistic that is capable of existence, and 

 does exist in species now living in alternative conditions depend- 

 ing upon the environic constellation encountered. That the 

 alteration is directly adaptive in its manifestation implies neither 

 purpose nor use, only that in the relation of water in the tissues, 

 mechanistic considerations show at once that only two possible 



