20 INTRODUCTOEY. 



On subjects so difficult as those of the order of Aristotle's 

 zoological and related works, and the supposed missing Intro- 

 duction to his History of Animals, dogmatic opinions are 

 out of place, and the following statements are made with 

 some diffidence. The History of Animals has an Introduc- 

 tion ending at i. c. 6, s. 4. Book i. of the Parts of Animals 

 was written as an introduction to the zoological and related 

 works generally, the first to be commenced having been the 

 History of Animals. During the production of this work, 

 it was found to be expedient to treat more fully some of the 

 subjects, such as progressive motion, respiration, sleep, 

 memory, and generation, in separate works, and thus 

 Aristotle had several of his zoological and related works on 

 hand at one and the same time. In connection with these 

 views, the fact already referred to, viz., the absence of a 

 reference to the History of Animals as a work in contem- 

 plation, is of some importance. Another important fact is 

 that Book vii. of that work, dealing with the development 

 and growth of man, is manifestly incomplete. This indi- 

 cates that the History of Animals occupied Aristotle's atten- 

 tion up to the close of his life. 



