PRINCIPLES OE SCIENTIFIC ARRANGEMENT. 135 
collectively the largest numbers of forms that in their 
several combinations are the most nearly equivalents, 
and may be almost paralleled in that quality to the alli¬ 
ance of species. Ascending from species, the naturalist 
scarcely hopes to find in the groups formed above them 
strict parallelism, although, to be logical, it should be 
so, and, where the combinations are most natural, it 
is most nearly so. Thus we do not again distinctly 
reach equivalents until we arrive at these families, which 
from linking together associations usually combined 
by an identity of instinct and functions, attach to them¬ 
selves greater interest, and form alliances pointed out 
by the finger of nature itself, which are therefore 
exempted from the arbitrary caprice of the constructive 
systematise 
It does not follow that families should be even nearly 
numerically equivalent, for a family may contain a few 
or a multitude of genera and species, or a multitude of 
genera and few species, or also a multitude of species 
and few genera. Families comprise groups of forms to 
which nature delegates the execution of certain duties 
and offices, and whether specifically numerous or few, 
we may assume they are sufficient for the object in¬ 
tended. If we can reach the motive that controls the 
peculiarities of the group, it is a golden key to the 
explanation of the structure of its constituents, and, 
perhaps might furnish us, if not with a positive clue, 
yet with a surmise as to the functions of the collateral 
groups of which it forms a member, and which diligent 
observation may accura 
Families, to be natural divisions, should stand in the 
same relationship to genera as species do, but from the 
opposite side, whatever the subdivisions are into which 
tely determine. 
