DIFFERENT BANK OP GROUPS. 26? 



and blending into each other at different points of con- 

 tact ; and representing each other by innumerable ana- 

 logies. If we begin with species, we find they form a 

 little circle of themselves : several of these little circles 

 congregate, as it were, and unite into a larger one ; this 

 circle in its turn unites to others, and is again involved 

 in a larger one ; " another and another yet succeed." 

 And thus does nature proceed ; every combination being 

 greater than the last : small circles are absorbed in 

 larger;- until she finally combines them all into one, 

 composed of the whole animal kingdom. It follows, 

 therefore, that although all natural groups are circles ; 

 yet are these circles of difitrent sizes, ranks, and value. 

 It consequently becomes necessary to designate these 

 different groups by particular names, that their com- 

 parative value may be understood, and that they may 

 become eflScient instruments for reasoning. 



(326.) It was long a favourite and an unqualified 

 assertion among naturalists, even of late years, that the 

 only absolute divisions in nature were species ; an as- 

 sertion which must now, however, be relinquished. 

 Species are as much connected among themselves, as are 

 genera ; the progression of affinity, in most cases, being 

 as gradual in one as in the other. Every natural group, 

 when perfect, is definite; because it not only shows a 

 circular series of affinities, but also a series of types or 

 representations. Thus, in many cases, we can demon- 

 strate the precise station of an animal ; at least, so far 

 as to form a pretty accurate opinion whether it stands 

 within the range of one circle, or enters the confines of 

 another immediately contiguous. The intervals between 

 one species and another is not wider, or more de- 

 cidedly marked, than that between two kindred genera : 

 for it frequently happens that varieties, as they are 

 called, occur between two supposed species, which leaves 

 us in doubt what to term them ; whereas we seldom 

 find that one genus blends into another so completely as 

 to render it impossible to say to which of them a par- 

 ticular species belongs. Nature's groups are, therefore. 



