336 PRACTICAL AND SCIENTIFIC ZOOLOGY. 
True it is that the author in question did not think it 
necessary to verify this group by tracing its parallel 
analogies in the next (the Merulide, or thrushes) which 
succeeds to it. Had he done so, he might probably 
have discovered that this, so far as concerns the order 
of the divisions just specified, were in reality an arti- 
ficial circle. And yet this conviction might not have 
been arrived at; for, if implicit reliance were placed upon 
the accuracy of this series, and we merely proceeded 
to fix upon the groups analogical to these in the next 
family circle, we should be at no loss to make them out 
in the following manner : — 
SHRIKES. oa Characters common to both. THRUSHES. 
- : e most completely organised of their re- 
Lanius. spective circles, Merula. 
Edolius. Feet very short. Brachypus. 
Tyrannus. Live in the vicinity of water. Crateropus. 
Ceblepyris. Aihreci toring long ; rump feathers more or Onalas. 
. rH 
Thamnophilus. Bill hooked at the tip. Myothera. 
(413.) Nothing™can be more perfect than the parallel 
analogies resulting from comparing these two groups ; 
and yet, as we have elsewhere demonstrated *, although 
the divisions and analogies in both these columns, taken 
separately, are correct, yet both are nevertheless disposed 
falsely. Here then is a group which has undergone two 
tests,—in the first instance, it has a verisimilitude of being 
truly circular, and then, being compared with an adjoin- 
ing group, it is found to possess parallel analogies thereto, 
— and yet the great error of its composition remains to 
be detected. How then are we to proceed in our pro- 
cess of verification? or how cana false circle be distin- 
guished from a trueone? It is here that the third test 
we have intimated, namely, the definite system of vari- 
ation, rust be resorted to, as a last and final criterion of 
the true value of all groups, supposed to be natural. 
(414.) Now, the principles by which all the vari- 
ations of form throughout the class of birds are regu- 
lated may be thus concisely stated :— First, we have, 
in the typical form, a union of the greatest number of 
* Northern Zoology, vol. ii. p. 164. 
