VERIFICATION OF GROUPS. 217 



genus Phanceus, 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 Phanceus 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- 



