WATER RELATIONS IN HIBERNATION. 237 



TABLE VI. 



SHOWING THE TEST MADE UPON CULTURE T 100 C, INTRODUCED INTO THE TUCSON 

 DESERTS IN JUNE, 1915, WHERE IT REPRODUCED, THE SAMPLE OF THE SECOND 

 SUMMER GENERATION, TAKEN TO CHICAGO, IN SEPTEMBER, AND SUBJECTED 

 TO THE SURVIVAL TEST IN THE WINTER OF 1915-16. 



These tests shown in the above tables have been made in 

 the wire tubes, placed close together, and having as far as 

 could be determined the same conditions during a given winter. 

 Undoubtedly the testing in tubes favors the culture in the elimina- 

 tion of possible enemies in the soil, and in fact, the survival of 

 the normal stocks in the tubes at Chicago is higher than in large 

 open cages, so that any action of the tube is favorable to survival 

 rather than otherwise. 



In all of the introductions precisely the same action is going 

 on, and in all of the tests the same result shows at about the same 

 rate of progression, namely, that the capacity to survive the 

 winter diminishes progressively as the number of generations 

 increases in which the stocks have lived under the conditions of 

 the Arizona deserts. The greatest change comes between intro- 

 duction and the hibernation of the first year. 



At Chicago for some years I have made routine tests of 

 certain of the activities concerned in hibernation, in that this 

 period of passing of the unfavorable portion of the year in their 

 habitat is a season of possible elimination, of possible selective 

 action, therefore, one of possible effectiveness in the evolution of 

 the population. In Table VII. I have shown a series of tests 

 made in the stock C 100 from the eighth to the eighteenth 

 generations, inclusive. These were all made in wire tubes sunk 

 in the ground, under similar conditions of soil, moisture and 

 climatic exposure. 



The tests in Table VII. show that in the preparation for 

 hibernation, on the average, eleven per cent., of the tested ma- 

 terials are not able to complete the preparations and do not enter 

 into hibernation. These will be found dead upon the surface of 



