210 The American Naturalist. [Mareh, 
of a class of bathmic or growth-energies. This is found in the 
phenomena of heredity. The most rational conception of this 
inheritance of structural characters is the transmission of a 
mode of motion from the soma to the germ-cells. This is a far 
more conceivable method than that of the transmission of 
particles of matter, other than thé ordinary material of nutri- 
tion. The bathmic theory of heredity bears about the same 
relation to a theory of transmission of the pangenes of Darwin, 
or the ids of Weismann, as the undulatory theory of light and 
other forms of radiant energy does to the molecular theory of 
Newton. I have therefore assumed asa working hypothesis the 
existence of the bathmic energy, and will enquire how far the 
facts in our possession sustain it. In doing so it will be neces- 
sary to elaborate the theory so as to render clearer its applica- 
tion to specific cases. The fact to be accounted for is its spe 
cialization into so many diverse specific forms. 
A further indication of the existence of the bathmic energy 
is the quantitative limitation to which growth is obedient. 
Thus the successive stages of embryonic growth are limited in 
number in each species. The dimensions of many species are 
limited within a definite range. The duration of life, or of the 
functioning organic machine, has a definite limit in time. Al 
this means that a certain limited quantity of energy is at the 
disposal of each individual organism. 
In “ The Origin of the Fittest,” I have endeavored to show 
what causes have been and are efficient in the production of 
different types of organic life, through the modifications of the 
bathmic energy. We will now briefly consider to the question 
of the origin of the living substance, protoplasm or sarcode, 
which exhibits bathmism. 
m vital 
should 
spontaneous generation of living organisms from inorganl¢ 
matter. Further, the principle of continuity leads us W ins 
that the energy which produced organic matter must y _ 
tical with or allied to that which is the efficient agent in PF 
