387 
The part entergogenic energy or entergogenism has played in the 
production of normal reactions, hypertrophy, etc., is well known, 
and the fact that an organism cannot move or respond to external 
stimuli without its aid needs no illustration. It seems equally plain 
that modifications of structure and form follow as the results of 
such repeated actions developing into habits, and this process neces- 
sarily ends in the permanent establishment or fixing of these modi- 
fications in varieties and species. 
This theory accounts satisfactorily for the so-called mysterious 
suitability of organic structures for the work they have to do. 
Such a force, capable of producing changes of structure and sensi- 
tive to the impinging action of external physical conditions, must 
work in directions determined by these two factors, z. e., the struc- 
tures already existent in the organism and the external forces them- 
selves. It is obvious that these actions and reactions must, as has 
been already stated above, produce habits and changes of structure 
which are direct responses to the environment. 
If one uses the Darwinian phraseology, one can say that the 
variations thus produced are natural selections, and I have called 
them in other publications physical selections, although it is likely 
that the use of the word selection in any way may convey an erro- 
neous idea of my meaning. Selection implies the choice of some 
characters or tendencies out of a number of others, and in the 
minds of most naturalists it also implies the survival of the fittest 
chosen by the working of the struggle for existence in two direc- 
tions, in one direction between contending organisms, and in the 
other between the same organisms and their surroundings. 
According to the opinions maintained in this paper, however, the 
organism has no such power of choosing, in the evolution of its 
characteristics. It is driven along certain paths and the influence 
of the struggle for existence and survival of the fittest is, if it has 
any influence at all, a perturbing force which has to be accounted 
for but does not seriously affect characteristics until after they origi- 
nate. Characteristics, therefore, are not evolved fortuitously and 
in indefinite numbers for the animal to select out those that are 
favorable and perpetuate only those, but according to the definite 
law of variation of Lamarck and Cope. 
The dynamical school does not reject the Darwinian doctrine, but 
it uses this hypothesis in its proper applications as a secondary law 
explanatory of certain phenomena of survival and perpetuation of 
