ZOOLOGICAL CLASSIFICATIONS. 



193 



markable traits of its organization, and the manner in which 

 its principal functions are exercised. 



365. The rules to be observed in arriving at a natural 

 classification of the animal kingdom are of extreme simplicity, 

 but often there is much difficulty in the application. They 

 may be reduced to two, for the object of the zoologist, in 

 establishing such a classification is, 



1st. To arrange animals into natural series, according to 

 the degree of respective affinities, that is to say, to distribute 

 them in such a manner that the distance from, or proxi- 

 mity to, a species, is the measure of the resemblance or 

 dissemblance. 



2nd. To divide and subdivide this series, according to the 

 principle of subordination of characters, that is to say, by 

 reason of the importance of the differences which these 

 animals present between them. 



366. To be satisfied, for example, of the affinity which 

 exists between the cat and the tiger, it is not necessary to 

 study the anatomy of these animals, for the external forms 

 translate, as it were, the character of the internal. But in a 

 great number of instances the examination of the internal 



Fig.132. Lernea. Fig. 135. Larvae of the Cyclops. 



structure becomes necessary, in order to avoid important 

 errors. Thus, for a long time, the relations which exist 

 between the lernese, parasitical animals with strange forms 



