56 ON THE CLASSIFICATION en 
filled up. Our suspicion, hee is metely ¢ — 
by our total ignorance of the manner in which nature 
passes from T'richas into the Ampelide, or fruit-eaters ; 
since, if this is the next family, its junction with that — 
of the Sylviade may be supposed to take place at this 
point. On the other, hand it must be remembered that 
many of the most indisputable passages or transitions 
in the ornithological system take place through groups 
which are terrestrial ; and, as Tichas is strictly of this 
description, it is contrary to sound logic to doubt that 
which is known, from our ignorance of that which may 
’ be unknown. 
(65.) The. intimate connection between Setophaga 
and Sylvicola enables us, in this place, to illustrate our 
views on one of the properties of typical or external 
groups. We have already had occasion to remark, 
that Mr. MacLeay long ago. pointed out the resemblance 
which such groups as these, in two or more different but 
contiguous circles, bear to each other ; and this resem- 
blance he has termed analogy. Now, this term appears 
strictly correct, when the groups in question are very 
comprehensive, and the intervening forms very dissi- 
milar. If, for instance, we look to the two typical 
divisions of vertebrated animals —as quadrupeds and — 
birds — and compare them with the corresponding groups 
of the Annulosa, or insects, we immediately perceive that 
there may be an analogy, but that there cannot exist 
any possible affinity. But how stands the case when 
the groups to be compared are smaller? Let us look to 
the circle of the Pariana to illustrate this question. 
(66.) The typical genera, as seen in the annexed dia- _ 
gram, are Parus and Sylvicola ; the subgenera Parus and 
Egithalus in. one, and Vermivora and Sylvicola in the 
other, are consequently the external or typical groups. 
Now, in support of our opinion, that what are to be 
termed analogies in larger groups, insensibly changers 
their character, and blend into close affinities in smaller — 
groups, we appeal to this circle. Is not the resem-_ 
