1388 : SPECIES AND BREEDS. 
covered with hair,—#in the cut of the ears, and 
their size, —in the length of their limbs, which 
are slender and long in some, short and thick in 
others, — in their various ways of living, — in. the 
different substances on which they feed, — and 
also in their distribution over the surface of the 
earth, whether circumscribed within certain lim- 
ited areas or scattered over a wider range. 
What is now the nature of these differences by 
which we distinguish Species? They are totally 
distinct from any of the categories on which Gen- 
era, Families, Orders, Classes, or Branches ar 
founded, and may readily be reduced to a few 
heads. They are differences in the proportion of 
the parts and in the absolute size of the whole - 
animal, in the color and general ornamentation 
of the surface of the body, and in the relations 
of the individuals to one another and to the 
world around. A farther analysis of other Gen- 
era would show us that among Birds, Reptiles, 
Fishes, and, in fact, throughout the Animal King- 
dom, Species of well-defined natural Genera dif- 
fer in the same way. Weare therefore justified 
in saying that the category of characters on 
which Species are based implies no structural 
differences, but presents the same structure com- 
bined under certain minor differences of size, 
proportion, and habits. All the specific characters 
stand in direct reference to the generic structure, 
