INFLUENCE OF ABSTRACT THOUGHT 25 



and animals known to him. Yet his purpose and 

 method mark him as the father of natural science. 

 He had the eye to observe and the mind to grasp the 

 relationships and the import of what he observed. 

 His attempt to classify animals according to the na- 

 ture of their teeth (dentition) has been criticized as 

 unsuccessful, but this principle of classification is still 

 of use, and may be regarded as typical of his mind, 

 at once careful and comprehensive. 



One instance of Aristotle's combining philosophi- 

 cal speculation with acute observation of natural 

 phenomena is afforded by his work on generation 

 and development. He knew that the transmission of 

 life deserves special study as the predominant func- 

 tion of the various species of plants and animals. 

 Deformed parents may have well-formed offspring. 

 Children may resemble grandparents rather than 

 parents. It is only toward the close of its develop- 

 ment that the embryo exhibits the characteristics of 

 its parent species. Aristotle traced with some care 

 the embryological development of the chick from 

 the fourth day of incubation. His knowledge of the 

 propagation of animals was, however, not sufficient to 

 make him reject the belief in spontaneous generation 

 from mud, sand, foam, and dew. His errors are 

 readily comprehensible, as, for example, in attrib- 

 uting spontaneous generation to eels, the habits and 

 mode of reproduction of which only recent studies 

 have made fully known. In regard to generation, as 

 in other scientific fields, the philosophic mind of Aris- 

 totle anticipated modern theories, and also raised 

 general questions only to be solved by later investi- 

 gation of the facts. 



