No. 643] STUDIES ON THE DURATION OF LIFE 



175 



short one wishes immediately to get a kind of knowledge 

 for this organism and character similar to that which 

 Johannsen (28, 29) got for the size character of beans 

 from his pure-line work. The first, and in a sense pre- 

 liminary, investigations on this problem will be presented 

 in this paper. Later in the series we expect to publish 

 much more extended and penetrating evidence on the 

 same problem. Some, however, must be presented early 

 in the series in order to make the account of subsequent 

 experiments intelligible. 



It is obvious that in the case of an organism like Droso- 

 phila it is impossible to have a pure-line in the strict sense 

 of Johannsen. The most that one can do is to have inbred 

 lines, and the most intense degree of inbreeding possible 

 in the premises is by brother X sister mating. The gen- 

 eral plan of the experiments reported in this paper can be 

 outlined as follows : 



1. Mate a virgin brother and sister, chosen at random 

 each from the same one of the original 5 foundation 

 stocks (cf. 27). 



2. Repeat this for as many pairs as the faciUties of the 

 laboratory make possible. 



3. Test the progeny of each mated pair separately for 

 duration of life, and form for each group of such progeny 

 a life table. 



4. Each such mated pair constitutes the beginning of a 

 line, in which at any time the processes noted under para- 

 graphs 1, 2, and 3 above could be repeated. In this paper 

 will be reported tlie results of one such repetition. 



The general technique of the experimental work has 

 been fully described in the first paper of this series and 

 need not be repeated. It should merely be emphasized 

 again that the environmental conditions in respect of 

 food, housing, temperature (25° C.) and atmospheric con- 

 ditions were identical for all the flies in the experiments 

 here reported. 



