224 BIOLOGICAL LECTURES. 



Why then call it "evolution"? Evidently not to recall the 

 defunct ideas of Bonnet, but to better define a new distinction 

 which has come into prominence largely as the result of Weis- 

 mann's own work. 



No one, as it seems to me, has defined the issue with which 

 we are now confronted more tersely than Mr. Mivart, when, in 

 opposition to Bourne, he declares that "the term evolution 

 may be employed as it has been, to denote that the succes- 

 sive formation of parts not previously existent is due not to 

 their imposition from without, but to their generation from 

 within." 



This statement compasses the whole situation : " the succes- 

 sive formation of parts not previously existent," represents the 

 accepted verdict on the old issue, and the expressions, " impo- 

 sition from without," and "generation from within " define the 

 new issue, which lies wholly this side of the old, as shown in 

 the Spencer- Weismann controversy. 1 



1 Spencer: " Every organism tends to become adapted to its conditions of life; 

 and all the structures of a species, accustomed through -multitudinous generations to 

 the climate, food, and various influences of its locality, are moulded into harmonious 

 cooperation favorable to life in that locality: the result being that in the development 

 of each yoiing individual, the tendencies conspire to produce the fit organization" 

 (Contemporary Review, Feb., 1893. Reprint, p. 36.) 



" The structure of any organism is a product of the almost infinite series of 

 actions and reactions to which all ancestral organisms have been exposed." 

 {Principles of Biology, I, p. 199.) 



Weismann : " Not only degenerations of parts, but even the harmonious and 

 efficacious metamorphosis of many cooperative parts can proceed without any 

 concurrence of the transmission of acquired characters." (Contemporary Review, 

 Sept., 1893, p. 314.) 



" The offspring owes its origin to a peculiar substance of extremely complicated 

 structure, viz., the germ-plasm. This substance can never be formed anew ; it can 

 only grow, multiply, and be transmitted from one generation to another. My 

 theory might therefore well be denominated blasto-genesis or origin from germ- 

 plasm, in contradistinction to Darwin's theory of pangenesis or origin from all 

 parts of the body." (The Germ-Plasm. Contemporary Science Series, 1893, 

 p. xiii.) 



