THE ORIGIN OF SPECIES. 59 



bryologists to formulate the law that the history 

 of the development of the individual presents in epi- 

 tome the history of the development of its kind; or, 

 as it is expressed in technical language, that the 

 history of the ontogenetic development of any form 

 of life is an expression of its phylogenetic develop- 

 ment. This formula serves as a key to a labyrinth of 

 facts, which are all plain and intelligible with its aid ; 

 but are so far from being intelligible without its aid, 

 that no other general explanation of them has ever 

 been attempted. On this formula, which involves the 

 assumption of the " Darwinian theory " in its widest 

 application, rests the whole structure of the science 

 of comparative embryology, to which of late years so 

 much attention has been devoted, that it may fairly be 

 said to constitute more than the half of zoological 

 science. 



The Science of Biology. Closely associated with 

 the spread of " Darwinian theories " came the recogni- 

 tion of the fundamental unity of animal and vegetable 

 life. The chief aids to this synthesis were the know- 

 ledge of the nature of protoplasm as the physical basis 

 of life, a knowledge popularized in England chiefly 

 through the writings of Professor Huxley ; and the 

 knowledge of the nature of the so-called "cell," as 

 the essential unit equally of animal and of vegetable 

 life, which had been already made known by Schwann. 

 The influence of these facts may be traced in the 

 introduction of the term Biology, to indicate a branch 

 of science which treats of those general laws of life 



