22 HELEN DEAN KING AND HENRY H. DONALDSON 



Since a graphic representation of the data will bring out 

 more clearly the changes in body growth with age in succes- 

 sive generations of these rats, graphs for the growth of the 

 males, constructed from data in tables 1 to 3, are shown in 

 chart 2. 



All three graphs in chart 2 run close together throughout 

 their entire course, especially so at the beginning, where they 

 have been separated somewhat more than the data warrant 

 in order that individual graphs can be clearly followed. 



The most important fact brought out in chart 2 is that body 

 growth in captive gray males is accelerated during the period 

 preceding puberty as the generations advance. The graph 

 for the second group (fifth to seventh generations) runs 

 slightly higher than that for the first group (second to fourth 

 generations) from its beginning. The graph for the third 

 group (eighth to tenth generations) crosses that for the 

 second group at the 120-day period and then runs higher than 

 either of the other graphs up to the 212-day period, subse- 

 quently falling to the level of that for the first group. The 

 fact that males of the last group did not attain as heavy a 

 weight in adult life as did those of the second group is not 

 significant, since the growth of these rats during adult life 

 was probably affected somewhat by unfavorable conditions 

 in the colony (chart 1). 



Growth graphs for the females in the three generation 

 groups are shown in chart 3. These graphs were constructed 

 from the data in tables 1 to 3. 



Growth graphs for females (chart 3) differ from those 

 males (chart 2) in two respects: 1) they are more widely 

 separated throughout the greater part of their course; 2) all 

 of them run at a lower level, since gray females are, on the 

 average, much smaller than males at all age periods after 

 weaning. 



The graphs in chart 3 run very close together up to the 

 100-day period, when they begin to diverge. A progressive 

 change in the form of the graphs as the generations advanced 

 is not as clearly marked as in the case of the males. The 



