I. LIFE PROCESSES 35 



Gray males of the tenth generation tended to be somewhat 

 more variable in body weight during early postnatal life than 

 did males of the first generation, and maximum variability 

 came at an earlier age (table 4). Since, however, differences 

 between the maximum coefficients, and between correspond- 

 ing coefficients for all age periods up to and including I'JU 

 days, are not statistically important, it appears that no sig- 

 nificant change in body-weight variability had occurred dur- 

 ing early life. 



Variability in body weight during adult life had changed 

 considerably at the end of ten generations. In males <>t' tin- 

 tenth generation variability decreased rapidly, after attain- 

 ing its maximum at the ninety-day period, and subsequently 

 was much less than that in males of the first generation. The 

 size of the coefficient for the age period of 120 days indicates 

 a drop of 6.7 2.50 from the maximum ; at age periods from 

 151 to 578 days differences between the corresponding coef- 

 ficients for the two series are well over three times their 

 probable errors. In a single instance such a difference would 

 not be deemed of much statistical value, but the fact that this 

 difference is found at fifteen consecutive age periods, coyer* 

 ing about one-half of the life span of the individuals, adds 

 considerably to its importance. The conclusion seems justi- 

 fied that gray males of the tenth generation were less variable 

 in body weight during adult life than were males of the first 

 generation. 



A comparison of corresponding coefliric-nt> in table 4 indi- 

 cates that gray males of the first generation wen- signifi- 

 cantly more variable in body weight at all age periods from 

 60 to 395 days than were stock albino males. Gray males 

 of the tenth generation showed a body-weight variability up 

 to the age of 151 days that was greater than that in albino 

 males of like ages, but variability in adult life was about tin- 

 same in the two series. It is evident, therefore, that the 

 trend of variability in captive gray males, as the generations 

 advanced, was toward that found in stock albino males. 



