168 ( ,4 ) 



scarcely born into a sand-lance, a human being climbed 

 the complete scale, and stood easily the chief of the 

 whole ? 



In the cases of species, where some individuals de- 

 velop farther than others, we say the former possess 

 more growth-force, or "vigor," than the latter. We 

 may therefore say that higher types of structure possess 

 more "vigor" than the lower. This, -however, we do 

 not know to be true, nor can we readily find means to 

 demonstrate it. 



The food which is taken by an adult animal is either 

 assimilated, to be consumed .in immediate activity of 

 some kind, or stored for future use, and the excess is 

 rejected from the body.;.' We have no reason to suppose 

 that the same kind .of material could be made to sub- 

 serve the production of life-force by any other jneans than 

 that furnished by a Hying animal organism. > -/The mate- 

 rial from which this organism is constructed is derived 

 first from the parent, and afterward from the food, etc., 

 assimilated by the individual itself so long as growth 

 continues. As it is the activity of assimilation directed 

 to a special end during this latter period which we sup- 

 pose to be increased in accelerated development, the 

 acceleration is evidently not brought about by increased 

 facilities for obtaining the means of life which the same 

 individual possesses as an adult. That it is not in con- 

 sequence of such increased facilities possessed by its 

 parents over those of the type preceding it, seems 

 equally improbable when we consider that the charac- 

 ters in which the parent's advance has appeared are 

 rarely of a nature to increase those facilities. 



The nearest approach to an explanation that can be 

 offered appears to be somewhat in the following direction : 



