DIFFICULTIES OF A FIRST ARRANGEMENT. 203 
were no progression of developement, all animals 
would be equally perfect—that is to say, have the 
same complexity of structure. Here, then, lies his 
difficulty. He perceives, perhaps, an evident affinity 
between two groups, by species which seem to blend 
them together, and to conduct him, by an almost 
insensible gradation, from one to the other. He 
therefore concludes this to be the natural series, and 
he approximates them accordingly: presently, how- 
ever, upon looking more attentively to his other 
unsorted groups, he finds not only one, but several, 
each of which, in some way or other, shows an ap- 
proximation just as close to his first group, as that 
does which he has previously made to follow it ; and 
he is as much at a loss how to dispose his groups 
in natural succession, as he was how to place the 
species which they contain. The same results also 
attend his attempts at improving his arrangement of 
groups: what is gained by shifting one so as to 
follow another, is lost by dissevering it from that 
with which it was previously united: until, with all his 
assiduity and trials, he finds there is still a remnant 
of “ unknown things,” which stand disconnected, as 
it were, from the series he has formed; and which 
cannot be made to fall into place by any contrivance 
he can devise. 
(138.) Now, the first question which arises in 
such a state of things—a state which every naturalist 
has repeatedly experienced, — is this ;—— What is 
the series of nature? Is it simple, or complex? 
and in what manner, or by what rules, am I to dis- 
tinguish the different natures of all these compli- 
cated relationships or resemblances, so as to deter- 
