REPRODUCTION, PUBERTY AND LONGEVITY. 233 



We may have these two factors in three combinations ; first, when 

 both factors are relatively low ; second, when one factor is low and 

 the other is high; and third, when both factors are relatively high. 

 In the first case we have the lowest forms of animal life, among 

 which we may include the worms. The second case is in two 

 forms, (a) those in which, the activity is low and the time is high 

 as in turtles, shell fish and degenerating forms of parasites, and 

 (b) those in which the activity is high and the time is low, as in 

 insects and most birds. In the third case we have the higher 

 mammals, and we find their height in the scale proportionately to 

 the product of these two factors. 



SELECTED CASES FOR COMPARISON. 



By taking a series of cases among the higher mammals in 

 which the activity does not vary greatly and in which the length 

 of time before reproduction is pretty accurately known, and by 

 making a diagram for this series of cases, we have the diagonal 

 line shown in Fig. n. If we were to make another diagram in 

 which the figures at the side represented the inherited mental power 

 of these classes of individuals instead of their average ages at 

 reproduction, we would draw practically the same diagonal line. 

 We thus see that the quality of the inheritance is proportional to 

 the factor time. We are able to determine this pretty accurately 

 because time may be expressed numerically. Unfortunately the fac- 

 tor activity cannot be so definitely known, but by comparing such 

 animals as the tortoise and the parrot, hibernating and non-hiber- 

 nating animals, and our observations that, as far as known, great 

 men have been the sons of mentally active men, we may be quite 

 sure that we would find the same proportionalism for activity when 

 the fcto* time was constant. 



