274 EVOLUTION IN BIOLOGY. [LECT. 



XI. 



EVOLUTION IN BIOLOGY. 



IN the former half of the eighteenth century, the term 

 " evolution " was introduced into biological writings, in 

 order to denote the mode in which some of the most 

 eminent physiologists of that time conceived that 

 the generation of living things took place ; in opposi- 

 tion to the hypothesis advocated, in the preceding 

 century, by Harvey in that remarkable work l which 

 would give him a claim to rank among the founders 

 of biological science, even had he not been the dis- 

 coverer of the circulation of the blood. 



One of Harvey's prime objects is to defend and 

 establish, on the basis of direct observation, the 

 opinion already held by Aristotle ; that, in the higher 

 animals at any rate, the formation of the new organism 

 by the process of generation takes place, not suddenly, 

 by simultaneous accretion of rudiments of all, or of the 

 most important, of the organs of the adult; nor by 

 sudden metamorphosis of a formative substance into a 

 miniature of the whole, which subsequently grows ; 

 but by epigenesis, or successive differentiation of a 



1 The " Exercitationes de Generations Animalium," which Dr. George 

 Ent extracted from him and published in 1651. 



