I. LIFE PROCESSES 45 



The changes in the average length of the reproductive 

 period as the generations advanced are indicated by the graph 

 in chart 7, constructed from data in table 6. 



A change in the average length of the reproductive period 

 at the end of three successive generations is indicated by the 

 course of the graph in chart 7. The rise in the graph at the 

 fourth generation denotes an increase of thirty days over the 

 length of this period in females of the first generation. 



500 

 280 

 260 

 240 

 220 

 200 

 180 



Generotion 



1 234567 



Chart 7 Showing the length of the reproductive period in different generations 

 of captive gray females. 



Another upward turn in the graph at the seventh generation 

 is indicative of a further gain of thirty-two days. The hiuhot 

 point in the graph, at the eighth generation, marks a repro- 

 ductive period extending over 286 days. The average repro- 

 ductive life of females in the last three generations was sev- 

 enty days longer than that in females of the first generation. 

 From the data presented in this section, it appears that t In- 

 duration of reproductive life in gray females changed consid- 

 erably in the course of nine generations. Breeding began at 

 an earlier age as the generations advanced, therefore the 

 average length of the reproductive period was increased in 

 later generations by about two months. 



