2 8 BIOLOGICAL LECTURES. 



What it is that makes crosses or hybrids more variable and 

 often more vigorous than inbred forms must also have a 

 dynamic explanation, since there can be no increased activity 

 of metabolic processes without an increased expenditure of 

 energy and an increased rate of molecular transformation. 



Variations cannot be spontaneous, as Darwin himself was 

 aware. The only way in which they can be supposed to have 

 arisen is by the blending of molecular dynamical systems of dif- 

 fering initial potential strengths, by the conjugation of sex-cells 

 (reciprocal integration), and by means of variations in the inter- 

 actions of such resultant systems with their surroundings. 

 This, however, Weismann and his followers deny, though no 

 proof whatever has been offered that such is not the fact. 

 Indeed, it is probable that so long as the ultimate machinery 

 of metabolism is beyond the reach of ocular demonstration, 

 there can be no proof or disproof of the position assumed by 

 the preformationists or Neo-Darwinists. Such proof or dis- 

 proof is, however, non-essential, since we are forbidden by the 

 first principles of dynamics to assume that transformation of 

 any living physical system whatever can occur without involving 

 some forces or influences that emanate from the external world. 1 

 The separation and evaluation of the internal and external 

 forces, incident to the manifestation of life, in the present 

 state of our knowledge, and from the very nature of the case, 

 plainly transcends the capacity of present available experimental 

 methods in biology. The discussion as to whether " acquired 

 characters " are inherited can, therefore, have but one outcome, 

 since external forces can never be excluded in considering the 

 life-history of any organism. 



Nageli, in seeking to account for the phenomena of growth, 



1 " Some of the exponents of this [preformation] theory of heredity have at- 

 tempted to elude the difficulty of placing a whole world of wonders within a body 

 so small and so devoid of structure as a germ, by using the phrase structureless 

 germs (F. Galton, Blood-relationship, Proc. Roy. Soc., 1872). Now one material 

 system can differ from another only in the configuration and motion which it has 

 at a given instant. To explain differences of function and development of a germ 

 without assuming differences of structure is, therefore, to admit that the proper- 

 ties of a germ are not those of a purely material system." JAMES CLERK-MAX- 

 WELL, article Atom, Encycl. Britan., 9 th ed., vol. Ill, p. 42, 1878. 



