112 FAMILY CHARACTERISTICS. 
It has been a very simple matter to establish such 
groups according to the superficial method that 
has been pursued, for the fact that they are de- 
termined by external outline renders the recogni- 
tion of them easy and in many instances almost 
instinctive; but it is very difficult to characterize 
them, or, in other words, to trace the connection 
between form and structure. Indeed, many 
naturalists do not admit that Families are based 
upon form; and it was in trying to account for 
the facility with which they detect these groups, 
while they find it so difficult to characterize 
them, that I perceived them to be always associat- 
ed with peculiarities of form. Naturalists have 
established Families simply by bringing together 
a number of animals resembling each other more 
or less closely, and, taking usually the name of 
the Genus to which the best known among them 
belongs, they have given it a patronymic termi- 
nation to designate the Family, and allowed the 
matter to rest there, sometimes without even at- 
tempting any description corresponding to those 
by which Genus and Species are commonly de- 
fined. 
For instance, from Canis, the Dog, Canide has 
been formed, to designate the whole Family of 
Dogs, Wolves, Foxes, etc. Nothing can be more 
superficial than such a mode of classification ; 
and if these groups actually exist in Nature, they 
