128 THE CHARACTERS OF GENERA. 
Considering all these divisions of the Animal 
F’>~dom from this point of view, it is evident 
thay 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 zodlogists. 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 
