Method of Origin of New Species and Structures 417 



germinal determinants in a continuous line, but never from body 

 characters. And the fallacious physical basis given his theory by 

 Weismann has been replaced by a secure one supplied by Mendel- 

 ian studies, presently to be considered. Indeed, the modern con- 

 ceptions of heredity, based on Mendelian results, is a veritable 

 reincarnation of the central feature of Weismannism. 



Before leaving this part of the subject it is needful to say that 

 such evidence as does seem to favor a transmission of acquired 

 characters is found in connection with certain diseases. The cases 

 seem to hinge upon chemical changes produced in the blood, which, 

 circulating and diffusing throughout the whole body, can thus 

 reach the germ cells and through them the next generation. On 

 this basis, any acquired character which affects the chemistry of 

 the blood could, theoretically, be transmitted to the germ plasm 

 and the next generation, although changes which are simply of a 

 physical or mechanical nature could not. We have a close anal- 

 ogy in the relation of scion characters to stock characters in 

 grafting, already considered (page 350); for it appears to be 

 generally true that characters which are dependent upon the sap 

 can be extended or ''transmitted" from the scion to the stock, and 

 vice versa, while characters which are dependent upon the pro- 

 toplasm are confined, on the contrary, strictly to scion or stock 

 respectively. This principle of chemical transmission may yet 

 prove to be important in evolution, and may rehabilitate Darwin's 

 theory of pangenesis on a new basis; and it accords with the tend- 

 ency of all modern research to reduce natural phenomena to a 

 chemical foundation. Indeed, some students of the subject have 

 suggested that the chromosomes, those carriers of heredity in the 

 nuclei of cells, are simply collections of enzymes, each of which 

 controls some single process of development in the new individual. 



The study of the problems of evolution exhibits three separate 

 epochs. The first was that of speculation from impressions, cul- 

 minating in the theories of Lamarck. The second was that of 

 induction from observation, inaugurated and carried to highest 



