210 ESSAY ON CLASSIFICATION. 



together, have we not, as characteristic of their systems, 

 the very words by which every one distinguishes the most 

 prominent features of the body of the higher animals, 

 when speaking of blood relations, of blood and bones, or 

 of having flesh and nerve 1 



Neither of these observers has probably been conscious 

 of the identity of his classification with that of Ins prede- 

 cessors ; nor, indeed, should we consider either of them 

 as superfluous, inasmuch as it makes prominent features 

 more or less different from those insisted upon by the 

 others ; nor ought any one to suppose that with all of 

 them the field is exhausted, and that there is no more 

 room for new systems upon that very first distinction 

 among animals. 1 As long as men inquire, they will find 

 opportunities to know more upon these topics than those 

 who have gone before them, so inexhaustibly rich is nature 

 in the innermost diversity of her treasures of beauty, order, 

 and intelligence. 



So, instead of discarding all the systems, which have 

 thus far had little or no influence upon the progress of 

 science, either because they are based upon principles not 

 generally acknowledged or considered worthy of confi- 

 dence, I have carefully studied them with the view of 

 ascertaining what there may be true in them, from the 

 standing-point from which their authors have considered 

 the animal kingdom ; and I own that I have often derived 

 more information from such a careful consideration than 

 I had at first expected. 



1 By way of an example, I would what is observed in any of the Inver- 



taention the mode of reproduction, tebrata, that the animal kingdom, 



The formation of the egg in Verte- classified according to these facts, 



brata ; its origin, in all of them, in a would again be divided into two great 



more or less complicated Graafian groups, corresponding to the Verte- 



vesicle, in which it is nursed ; the brata and Invertebrata of Lamarck, 



formation and development of the or to the Flesh- and Gut-Animals of 



embryo up to a certain period, etc., Oken, or the Enaima and Anaima of 



etc., are so completely different from Aristotle, etc. 



