DIFFERENT RANK OF GROUPS. 267 
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 different 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 efficient instruments for reasoning. 
a 
(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, 
