422 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



also supported by the presence of a contact furrow on 

 the dorsum of the earliest age of the conch in the spe- 

 cialized and highly tachygenic forms of the Goniati- 

 tinae of the Devonian and of all the remaining ammo- 

 noids to the end of the Cretaceous. 



"9. These cumulative results favor the theory of 

 tachygenesis (acceleration) and diplogenesis, and are 

 opposed to the Weismannian hypothesis of the sub- 

 division of the body into two essentially distinct kinds 

 of plasm, the germ-plasm, which receives and trans- 

 mits acquired characteristics, and the somatoplasm, 

 which, while it is capable of acquiring modifications, 

 either does not or cannot transmit them to descend- 

 ants. " {Proceedings American Philosophical Society, Vol. 

 XXXIL, p. 615). 



4. EVIDENCE FROM BREEDING. 



Under this head I cite the results of experience of 

 breeding of the domesticated Vertebrata. It is here 

 that we have had the best opportunity of testing the 

 possibility of the inheritance of acquired characters, 

 since the species in question have been the objects of 

 observation and experiment for a long period of time. 

 I especially avail myself of the writings in this con- 

 nection of Prof. Wm. H. Brewer, of Yale University, 

 President of the Agricultural Society of Connecticut. 

 The result of his long-continued observations is con- 

 tained in a series of papers in the journal Agricultural 

 Science of the years 1892-1893. He considers the sub- 

 ject under the following heads, viz. : The inheritance 

 of characters which are due to nutrition ; of those due 

 to the exercise of function ; of those due to disease ; 

 of those due to mutilation and injuries ; of those due 

 to habit, training, and education ; of those due to re- 



