THE PALEONTOLOGIC RECORD 481 
coloration, the response is entirely determined within the organism, which is 
adjusted to different intensities of stimuli and reacts according to its own 
method and on the basis of its own constitution, there being no specific reaction 
called forth by a given stimulus. 
I conclude in the light of these experiments that the production of heritable 
variations, slight or extreme, represents in these beetles the response of the 
germ plasm to stimuli. In my experiments these stimuli were external, but 
there is no a priori reason why they might not also be internal. 
I desire also to call your attention to some remarks by Loeb :* 
It is obvious that no theory of evolution can be true which disagrees with 
the fundamental facts of heredity. It is the merit of de Vries to have shown 
that a mutation of species can be directly observed in certain groups of plants, 
and he has further shown that the changes occur by jumps, not gradually. This 
fact harmonizes with the consequence to be drawn from Mendel’s experiments 
that each individual characteristic of a species is represented by an individual 
determinant in the germ. This determinant may be a definite chemical com- 
pound. The transition or mutation from one form into another is therefore 
only possible through the addition or disappearance of one or more of the 
characteristics of determinants. If this view can be applied generally, it is 
just as inconceivable that there should be gradual variation of an individual 
characteristic and intermediary stages between two elementary mutations, as 
that there should be gradual transitions between one alcohol and its next 
neighbor in a chemical series. 
To summarize my own opinions on this subject: 
1. I think it very doubtful if paleontology can make any especially 
valuable contribution to our knowledge of the process or causes of the 
evolution of organisms, and that this field must be surrendered to the 
experimental biologist. | 
2. The results of experimental work indicate that the process is not 
by the gradual transformation of species, but by saltation. However, 
the former method has not been shown impossible. 
3. Experimental investigations also indicate that the cause of evo- 
lution is by the environment acting on an organism capable of respond- 
ing to it. 
4. The causes of evolution are chemical in their nature, and the aid 
of the chemist is necessary for their thorough elucidation. 
°«*The Dynamics of Living Matter,” p. 3, 1906. 
VOL. LXXVII.—33. 
