24 HELEN DEA1ST KING AND HENRY H. DONALDSON 



graph for the third group of females, however, runs higher 

 than either of the other graphs up to the 200-day period, thus 

 indicating that females in the later generations had a rela- 

 tively greater acceleration in body growth during the early 

 portion of the life span than did females in the earlier gen- 

 erations. 



Females in the later generations were heavier in adult life 

 than were those in the earlier generations, as the position of 

 the graphs in chart 3 shows. That the graph for the third 

 group of females runs lower than that for the second group 

 during the latter part of its course is due, doubtless, to the 

 same cause as that advanced for a similar relation in cor- 

 responding graphs for males (chart 2). 



In order to show the change in body growth of males that 

 had occurred at the end of ten generations, data for body 

 weights at different age periods for individuals in the first 

 and for those in the tenth generation are given in table 4. 

 The data for the first generation are reproduced from a 

 previous publication (King, '23). 



Data for average body weights, as given in table 4, are 

 shown graphically in chart 4. This chart also contains a 

 graph (3) for a series of stock albino males that were reared 

 under similar conditions of housing as the gray rats, although 

 they were fed on 'table scraps,' not on the ration that for 

 some years has been given to all rats in the colony. Data 

 from which graph 3 was constructed were given in a previous 

 paper (King, '15 a, table 3). 



In chart 4 the graph (2) for gray males of the first genera- 

 tion runs at a much lower level throughout its entire course 

 than the graph (2) for males of the tenth generation. It 

 shows no pronounced curve at its beginning, but mounts 

 steadily upward and tends to be a straight line. 



Graph 2, that for males of the tenth generation, is also a 

 nearly straight line from its beginning up to about the 120- 

 day period, when it curves upward. At the 240-day period 

 the graph begins to flatten, and subsequently it runs fairly 

 straight until its end. The space between graph 1 and graph 



