154 



THE AMERICAN NATURALIST [Vol. XLIX 



we find a chief cause of progressive evolution. Jennings 

 speaks of the principle involved here as the "Law of the 

 readier resolution of physiological states after repeti- 

 tion," and, similarly, I think we must recognize a "Law 

 of the accumulation of surplus energy" as resulting 

 therefrom. Let us look at the case of the accumulation 

 of food-yolk by the egg-cell a little more closely from 

 this point of view. Every cell takes in a certain amount 

 of potential energy in the form of food for its own use. 

 If it leads an active life either as an independent or- 

 ganism or as a constituent part of an organism, it may 

 expend by far the greater part, possibly even the whole, 

 of that energy upon its own requirements, but usually 

 something is left over to be handed down to its imme- 

 diate descendants. If, on the other hand, the cell ex- 

 hibits very little activity and expends very little energy, 

 while placed in an environment in which food is abun- 

 dant, it will tend to accumulate surplus energy in excess 

 of its own needs. Such is the case with the egg-cells 

 of the multicellular animals and plants. Moreover, the 

 oftener the process of absorbing food-material is re- 

 peated the easier does it become; in fact, the egg-cell es- 

 tablishes a habit of storing up reserve material or food- 

 yolk. Inasmuch as it is a blastogenic character, there 

 can be no objection to the supposition that this habit 

 will be inherited by future generations of egg-cells. In- 

 deed we are obliged to assume that this will be the case, 

 for we know that the protoplasm of each succeeding gen- 

 eration of egg-cells is directly continuous with that of 

 the preceding generation. We thus get at any rate a 

 possibility of the progressive accumulation of potential 

 energy in the germ-cells of successive generations of 

 multicellular organisms, and, of course, the same argu- 

 ment holds good with regard to sueeossive generations 

 of Protista. 



It would seem that progressive evolution must follow 

 as a necessary result of the law of the accumulation of 

 surplus energy in all cases where there is nothing to 



