PROPERTIES OF GROUPS. 329 



three lesser ones, and so on, until we arrive at the lowest 

 groups in nature, which are called sub-genera. 



(402.) Some other properties of natural groups need 

 not here be alluded to, since they belong to a more 

 intimate acquaintance with the science than is usually 

 aimed at by beginners, and they have already been dis- 

 cussed in the body of this work. So soon as the 

 student understands so much of the nature of groups as 

 we have now endeavoured familiarly to explain, he will 

 be fully competent to pursue the subject as discussed in 

 the former chapters. There are, nevertheless, certain 

 other properties in natural groups, which, the young 

 naturalist should be acquainted with ; because they serve 

 as tests by which all groups should be tried ; as these 

 enter into the laws of verification., they will not now 

 be considered. 



(403.) After perusing thus far, the student may pro- 

 bably say, " I understand that all natural groups form 

 their own circle; and that each circle contains three smaller 

 ones, two of which are typical, and one aberrant : but 

 in what manner am I to prove my circle, whether it be 

 natural, since I have been told that false circles can be 

 made ? If, for instance, I am desirous of discovering, 

 without the aid of books, the manner in which the 

 family of thrushes (Merulida Sw.*) describe their cir- 

 cle of affinity, what check have I upon my own arrange- 

 ment, after I have placed these birds in such a way as 

 to exhibit a circle ? Must I be guided only by what 

 appears to be the circle of affinity ? or are there other 

 circumstances by which my circle is to be verified, and 

 my fancy kept in check ? " 



(404.) These are questions which may naturally be 

 asked, and which we shall now proceed to answer. There 

 are three modes, or processes, then, by which natural 

 groups are to be verified. 1. By their circularity. 2. 

 By the parallel analogy of their contents to other groups; 

 and, 3. By the order in which their types or subordinate 

 divisions occur. This latter may be termed the theory 



* See their natural arrangement in Northern Zoology, vol. ii. p. 149. 



