VERIFICATION OF GROUPS. 217 
genus Phaneus, belonging to the same order, 
we find another celebrated writer declaring that, 
in this, all the species can be referred to five 
types: now the question is, how can these different 
opinions be verified, or made to agree? The rule, 
were the groups of a higher order, would be obvious. 
Do each of these divisions form circles of their own? 
if not, they are unnatural: but this test cannot be 
often applied to a genera; because it rarely happens 
that their sub-genera are so abundant in species as 
to form complete circles. Yet there are two modes 
which can still be resorted to, independent of any 
assumed theory, for ascertaining what is the de- 
terminate number in the groups before us. First, 
we should endeavour to see how far the seven 
divisions in one can be reduced to five, so that two 
of them are absorbed, as it were, into the others. 
If we find this to be impracticable, without destroy- 
ing the equality of the divisions, we should reverse 
the experiment, and ascertain how far the five 
groups of Phaneus can be made into seven. If we 
succeed in this, or in the other, we establish an 
agreement; and, so far as we have then gone, there 
is presumptive evidence to favour the supposition 
that one or other of these numbers may be prevalent 
in other genera. The truth of such a theory, whether 
it be in favour of five, or seven, or any other 
definite number, depends on the extent to which it 
can be verified by observed or known facts. So 
that, although we may be able, as in the above 
instance, to make the divisions of two genera agree 
in their determinate number, and may therefore 
feel a disposition to build a theory upon such a coin- 
