340 PRACTICAL AND SCIENTIFIC ZOOLOGY. 



not enough for demonstration : its circularity must be 

 made out, and its contents submitted to the very same 

 tests that have been applied to the entire family. If 

 the MYOTHERIN.E, then, form a truly natural, and, there- 

 fore, a circular group, its component parts will re- 

 present all the divisions of its own family ; and we 

 shall find the subordinate variations analogically repre- 

 senting Merula, Crateropus, Oriolus, and Brachypus. So 

 far is this beautiful uniformity of consistent and definite 

 variation from being chimerical, that we have, in another 

 work *, selected the MYOTHERIN^E for this especial pur- 

 pose, and have demonstrated that they form a natural 

 group, capable of the same degree of verification as we 

 have been here insisting upon. To that work we must 

 refer the reader, who desires to see in what manner 

 relations of analogy, in so small a circle, can be made 

 out. To pursue the subject farther, on the present 

 occasion, will be needless. We have confined our illus- 

 trations to ornithology; but it must be remembered 

 that the same laws are applicable to every group in the 

 animal kingdom. 



(419') Natural groups are thus to be detected by 

 three different tests : 1. By their simple series of circular 

 affinity ; 2. By the theory of analogy ; and, 3. By the 

 theory of variation. We draw the first of these proofs 

 from affinity ; but the two latter entirely depend upon 

 analogy. No group which will not bear these tests can 

 be natural ; whereas, if it will stand such an ordeal, it 

 has passed all the trials necessary to establish its cor- 

 rectness. 



(420.) We trust that the young naturalist will now 

 see the truth of the observation long ago made by a 

 well-known naturalist, that nothing can be easier than 

 to make circles, provided it is not thought necessary to 

 prove them : in other words, to give them more value 

 than they possess, either from mere assertion, or from 

 wearing an appearance, at first sight, of being really 

 what they are affirmed. We trust, moreover, that he 



* Northern Zoology, vol. ii. p. 168. 



