458 Mr. N. A. Vicors on the Natural Affinities 
other would leave us in some doubt as to where the line of de- 
marcation may be drawn between them, did not the conforma- 
tion of the foot of the Certhiade evidently evince a deviation 
from the perfect structure of the more typical Scansores, and thus 
distinguishing them as an aberrant group of the tribe, make it 
necessary that they should be placed in a separate family. 
The different structure of the foot from that of Picus thus 
brings us among the Certhiade. Here that member is not 
strictly scansorial. But a similar assistance to what is conferred 
on the Picide in climbing, by the two toes being placed behind, 
is afforded the Certhiade by the single hind toe being consi- 
derably longer and more robust than is usual among the PercA- 
ers. The affinity that brings these birds together in a natural 
group is thus preserved, not by an identical, but by a similar 
and equally effective mode of conformation. I feel some diffi- 
dence, I must confess, in infringing upon the usual and more 
vegular rules of systematic arrangement, by placing this family 
among the birds with true scansorial feet: but I am influenced 
by a consideration paramount to that of uniformity of system ; 
by observing, in fact, that the whole group of climbing birds be- 
fore us is united by strong natural affinities. And when I perceive 
a series of natural objects thus united, I draw the conclusion that 
it is the group which affords the character, and not the character 
which constitutes the group. —“‘ Scias," says the great master of 
natural science, ** characterem non constituere genus, sed genus 
characterem :— characterem non fluere e genere, sed genus e cha- 
ractere :—characterem non esse ut genus fiat, sed ut genus nosca- 
tur *."—In a group strongly and naturally united as that before 
us, the evanescence in any of its subordinate subdivisions of any 
particular character common to the rest, does not prove that 
the subdivision in which such a character disappears is incon- 
* Linn. Phil. Bot. p. 119. 
gruous 
