232 WILLIAM LAWRENCE TOWER. 



T 100 B, introduced 1912, now in hibernation in FI<J. 

 T 100 C, introduced 1915, now in hibernation in p4. 



Each introduction was taken from the stock at Chicago in 

 the following way : On emergence from hibernation the materials 

 were, of each sex, placed in containers, covered with a cloth, 

 and twenty to twenty-five of each sex removed without inspec- 

 tion, so that there would be no opportunity for selective action 

 on my part, and this parental group of forty to fifty individuals 

 were taken or sent at once to Tucson and placed in the cage 

 prepared with food to receive them. They were then allowed 

 to breed as a population. When the progeny of an introduced 

 group, or if at any other time the population was so large that 

 to breed all was impossible, the same impersonal method of 

 deriving the parental group was resorted to, and it seems highly 

 improbable that with these methods, any selective action could 

 have entered into the series of experiments. 



Each introduction has had the same method of derivation 

 from the basal stocks at Chicago, and the same treatment under 

 the conditions of experiment at Tucson, grown as populations, 

 treated as populations, and the results are of the population as 

 .a whole, and not of individual lines or mutants. 



The series has shown several interesting responses to the 

 introduction into the desert environment, but the most interesting 

 one is the development of a capacity to retain water in the tissues 

 of the second summer, or hibernating generation, instead of 

 eliminating it in preparation for hibernation. 



The development of this modification of the animal was first 

 discovered in F 6 of T 99, when a population of over four hundred 

 individuals of the second annual generation was sent to Chicago 

 early in September, 1910 (211 <? 234 9), placed in a cage in the 

 garden at Chicago, in size and construction like those at Tucson, 

 where they soon entered into hibernation, but absolutely failed 

 to survive the Chicago winter, and were completely eliminated, 

 while a culture of the parent stock in a cage six feet away showed 

 only the normal reaction to that particular winter. 



The following year, 1911, tests of this condition were made 

 as follows: T 99 in F 8 , of the second annual generation, and 

 T 100 in F 2 of the second annual generation were sent to Chicago 



