that connect the Orders and Families of Birds. 511 
of things in nature. The very perfection of my plan would in 
that case be of itself the most formidable obstacle to my convic- 
tion of its truth and justness. Still, however, sufficient grounds 
have been shown, I trust, to prove the general prevalence of the 
principle which it is my wish to establish: and when we see it 
carried to so considerable an extent; when we find nothing to 
contradict it either in the groups which we already know, or in the 
species which are every day pouring in upon us—we may infer 
from analogy, I take it for granted, that the principle itself is 
universal ; and that the deficiencies observable in our series are 
the result merely of our limited knowledge, and such as we may 
expect to see remedied as our acquaintance with nature becomes 
more extended. 
How far the details that have been entered into in the fore- 
going view of my subject are correct, it is not for me to deter- 
mine. I myself can detect many alterations that might take 
place, and many modifications that might be effected, without 
interfering with the general object of this investigation, or im- 
pugning the principles which it has been my wish to illustrate. 
Many of the different groups, for instance, might be enlarged at 
their extremes by important additions from the conterminous 
subdivisions, or might on the other hand be contracted by the 
transfer of a portion of their own extremes to the groups which 
adjoin them. Intervening assemblages might in like manner be 
formed out of the extremes on each side, and be separated from 
both, forming distinct and osculant orders or families between 
them, according to their extent and importance. Where there 
are no absolute divisions except species in nature,—and this from 
every observation I have been enabled to make I firmly believe 
to be the case,—every division which we are forced to institute 
in our arrangements for the convenience of illustration, and in- 
deed for the purpose of mutual communication with those who 
are 
