164 ESSAY ON CLASSIFICATION 



though to some extent there are differences in the form of the repre- 

 sentatives of one genus when compared to those of another genus; 

 but when rightly considered, these differences appear only as modi- 

 fications of the same type of forms. Just as there are more or less 

 elongated ellipses, so do we find the figure of the Badgers somewhat 

 more contracted than that of either the Bears, or the Raccoons, or 

 the Wolverines, that of the Wolverines somewhat more elongated 

 than that of the Raccoons; but the form is here as completely typical 

 as it is among the Viverrina, or among the Canina, or among the 

 Bradypodidae, or among the Delphinoidae, etc., etc. We must, there- 

 fore, exclude form from the characteristics of natural genera, or at 

 least introduce it only as a modification of the typical form of natural 

 families. 



Of all the natural groups in the animal kingdom there remain 

 then only families and orders, for the distinction of which form 

 can apply as an essential criterion. But these two kinds of groups 

 are just those upon which zoologists are least agreed, so that it may 

 not be easy to find a division which all naturalists would agree to 

 take as an example of a natural order. Let us, however, do our best 

 to settle the difficulty and suppose for a moment that what has been 

 said above respecting the orders is well founded, that orders are 

 natural groups characterized by the degree of complication of their 

 structure and expressing the respective rank of these groups in their 

 class, then we shall find less difficulty in pointing out some few 

 groups which could be generally considered as orders. I suppose 

 most naturalists would agree, for instance, that among Reptiles the 

 Chelonians constitute a natural order; that among Fishes, Sharks 

 and Skates constitute an order also; and if any one would urge the 

 necessity of associating also the Cyclostomes with them, it would 

 only the better serve my purposes. Ganoids, even circumscribed 

 within narrower limits than those I had assigned to them, and per- 

 haps reduced to the extreme limits proposed for them by J. Miiller, 

 I am equally prepared to take as an example, though I have in 

 reality still some objections to this limitation, which, however, do 

 not interfere with my present object. Decapods, among Crustacea, 

 I suppose everybody would also admit as an order, and I do not 

 care here what other families are claimed besides Decapods to com- 

 plete the highest order of Crustacea. Among Acephala, I trust Bryo- 



