128 THE CHARACTERS OF GENERA. 



Considering all these divisions of the Animal 

 Kingdom from this point of view, it is evident 

 that the more comprehensive ones must be those 

 which are based on the broadest characters, 

 the Branches, as united upon plan of structure, 

 standing of course at the head ; next to these 

 the Classes, since the general mode of executing 

 the plan presents a wider category of characters 

 than the complication of structure on which Or- 

 ders rest; after Orders come Families, or the 

 patterns of form in which these greater or less 

 complications of structure are clothed ; and, pro- 

 ceeding in the same way from more general to 

 more special considerations, we can have no other 

 category of structure as characteristic of Genera 

 than the details of. structure by which members 

 of the same Family may differ from each other, 

 and this I consider as the only true basis on 

 which to limit Genera, while it is at the same 

 time in perfect accordance with the practice of 

 the most eminent modern zoologists. It is in 

 this way that Cuvier has distinguished the large 

 number of Genera he has characterized in his 

 great Natural History of the Fishes, published 

 in connection with Valenciennes. Latreille has 

 done the same for the Crustacea and Insects ; and 

 Milne-Edwards, with the co-operation of Haime, 

 has recently proceeded upon the same principle in 

 characterizing a great number of Genera among 



