I. LIFE PROCESSES 



43 



The average ages at which the first and the last litters 

 were cast by females of the different generations are shown 

 by graphs in chart 6. The graphs were constructed from 

 data given in table 6. 



500 

 480 

 460 

 440 

 420 

 400 

 380 

 360 

 340 

 320 

 300 

 280 

 260 

 40 

 220 

 200 

 J80 



Average Acje in 



Generation 



Chart 6 Graphs for captive gray females, showing the average age when the 

 first and when the last litter was cast. 



As indicated by the course of the lower graph in chart 6, 

 the average age at which females cast their first litters tended 

 to decrease from the first to the sixth generation. The late 

 beginning of reproduction in females of the seventh genera- 

 tion was due, probably, to the fact that these females did not 

 receive as adequate care as did those of the earlier and of the 

 later generations. With the improvement in general condi- 

 tions, the females again began breeding at a relatively early 



