CLASSIFICATION OF ANIMALS. 209 



Defects of this kind are to be found in many systems of 

 classification formed long after Aristotle's time, and it is 

 but fair to say that, considering the early period in which 

 he lived, he had clear conceptions of some of the chief 

 features of difference and similarity in animals, and that 

 he set forth these features and employed terms some of 

 which were certainly terms of classification. Further, 

 several of his groups were based on a consideration of 

 essential, and not arbitrary, characters of the animals com- 

 posing them, and many causes of difference were taken into 

 account, so that Aristotle may be fairly said to have at- 

 tempted to form a natural system of classification. For 

 these achievements, and they are considerable, he is entitled 

 to have the credit. More than this, perhaps, cannot be 

 claimed for him, yet the nature of his zoological writings 

 has often led to attempts to do this. For, reading them in 

 the light of modern zoological knowledge, it is easy to 

 interpret his statements as evidence of an elaborate scheme 

 of classification, and, when admiration for Aristotle is ex- 

 cessive, as it was in Cuvier and Owen, it becomes natural to 

 read into his words meanings which, probably, he himself 

 never intended. 



In the development of a science, a desire to classify very 

 soon shows itself, but, as Whewell has shown, the formation 

 of a systematic classification follows naturally only after 

 vast numbers of observations have been carefully made and 

 compared. Therefore, such a classification is not to be ex- 

 pected at a very early stage in the development of zoological 

 knowledge, such as that in Aristotle's time. Yet he formed 

 some general ideas of a classification based on a consideration 

 of structure and mode of life, thus forming groups, such as his 

 Ketode, Selache, Malakia, and Entoma, which could be more 

 easily described in this way. In the performance of this 

 task he made serious mistakes, but, as Whewell admits, 

 he may justly be regarded as the great Figure in the pre- 

 lude to that formation of Systems which took place in later 

 times. 



Aristotle repeatedly uses two classificatory terms, ysvor 

 igenos) and H^os {eidos), which are of very great importance, 

 but, before setting out the meanings of these terms, it will 

 be necessary to consider the meanings of the terms vTrepoxh 

 {hyperoche), exxejvVjs- (elleipsis) , and avay^oyUt (analogia), which 

 are of importance in his conceptions of y^vo^ and f?i5b,', 



Aristotle says that animals, such as birds, which have 



p 



