HISTORICAL DEVELOPMENT OF ZOOLOGY 445 



up to that time. Later work by the German scientist Max 

 Schultze showed that not only are plants and animals com- 

 posed of similar units (the cells), but the actual living ma- 

 terial, or protoplasm, is identical in plants and in animals. 



The Origin of Species. One of the outstanding contribu- 

 tions of the nineteenth century to scientific thought was the 

 serious study of evolution. 

 As a philosophical prin- 

 ciple evolution had been 

 discussed since the days 

 of Aristotle. No one per- 

 son has had greater effect 

 in stimulating thought 

 and research in natural sci- 

 ence than Charles Darwin 

 (Fig. 233), whose works 

 have been discussed in 

 another chapter. 



He brought together 

 huge volumes of facts 

 from nature in support 

 of his arguments. Such an 

 array of facts was never 

 before assembled. This 

 statement may be more 



readily appreciated when we understand the methods used in 

 science from its beginnings on down through the Middle Ages. 

 In all branches of learning, as well as in the sciences, the proof 

 of a statement or the validity of an expression rested upon 

 the statements of older writers. The words of an authority 

 passed for fact and were unquestioned. Science owes a debt 

 to the philosopher Roger Bacon for altering this manner of 

 getting at truth. Through his teaching in the thirteenth 

 century, — that we arrive at facts only by observation of 



Fig. 233. Charles Darwin 



