8 ON THE LAW WHICH HAS REGULATED 
the lines of affinity, as intricate as the twigs of a 
gnarled oak or the vascular system of the human 
body. Again, if we consider that we have only frag- 
ments of this vast system, the stem and main branches 
being represented by extinct species of which we have 
no knowledge, while a vast mass of limbs and boughs 
and minute twigs and scattered leaves is what we 
have to place in order, and determine the true posi- 
tion each originally occupied with regard to the others, 
the whole difficulty of the true Natural System of . 
classification becomes apparent to us. 
We shall thus find ourselves obliged to reject 
all those systems of classification which arrange 
species or groups in circles, as well as those 
which fix a definite number for the divisions of 
each group. The latter class have been very gener- 
ally rejected by naturalists, as contrary to nature, 
notwithstanding the ability with which they have 
been advocated ; but the circular system of affini- 
ties seems to have obtained a deeper hold, many 
eminent naturalists having to some extent adopted 
it. We have, however, never been able to find a 
case in which the circle has been closed by a 
direct and close affinity. In most cases a palpable 
analogy has been substituted, in others the affinity 
is very obscure or altogether doubtful. The com- 
plicated branching of the lines of affinities in 
extensive groups must also afford great facilities 
for giving a show of probability to any such 
purely artificial arrangements. Their death - blow 
