PROGRESS OF ICHTHYOLOGY. 407 



fishes, ranks as marked, as for example, to those of 

 mammifers. Thus the chondropterygians on the 

 one hand hold to reptiles by the organs of the 

 senses, and by those of generation in some ; and 

 they are related to mollusks and worms by the 

 imperfection of the skeleton in others. 



" As to ordinary fishes, if any part of the organi- 

 zation is found more developed in some than in 

 others, there does not result from this any pre-emi- 

 nence sufficiently marked, or of sufficient influence 

 upon their whole system, to oblige us to consult it 

 in the methodical arrangement. 



" We shall place them, therefore, nearly in the 

 order in which we have just explained their cha- 

 racters." 



I have extracted the whole of this passage, 

 because, though it is too technical to be understood 

 in detail by the general reader, those who have fol- 

 lowed with any interest the history of the attempts 

 at a natural classification in any department in 

 nature, will see here a fine example of the problems 

 which such attempts propose, of the difficulties 

 which it may present, and of the reasonings, la- 

 bours, cautions, and varied resources, by means of 

 which its solution is sought, when a great philoso- 

 phical naturalist girds himself to the task. We see 

 here, most instructively, how different the endea- 

 vour to frame such a natural system, is from the 

 procedure of an artificial system, which carries im- 

 peratively through the whole of a class of organized 



