46 Darwin, and after Darwin. 
contrary, it is a general rule that “the less any part of 
the organization is concerned with special habits, the 
more important it becomes for classification.” Now, 
from the point of view of special creation it is unin- 
telligible why unity of ideal should be most manifested 
by least important structures, whereas from the point of 
view of evolution it is to be expected that these life- 
serving structures should have been most liable to diver- 
gent modification in divergent lines of descent, or in 
adaptation to different conditions of life, while the trivial 
or less important characters should have been allowed 
to remain unmodified. Thus we can now understand 
why all primitive classifications were wrong in princi- 
ple when they went upon the assumption that divine 
ideals were best exhibited by resemblances between 
life-serving (and therefore adaptive) structures, with 
the result that whales were classed with fishes, birds 
with bats, and so on. Nevertheless, these primitive 
naturalists were quite logical ; for, from the premises 
furnished by the theory of special creation, it is much 
more reasonable to expect that unity of ideal should 
be shown in plainly adaptive characters than in trivial 
and more or less hidden anatomical characters. More- 
over, long after biological science had ceased con- 
sciously to follow any theological theory, the apparent 
axiom continued to be entertained, that structures of 
most importance to organisms must also be structures 
of most importance to systematists. And when at 
last, in the present century, this was found not to be 
the case, no reason could be suggested why it was not 
the case. But now we are able fully to explain this 
apparent anomaly. 
Once more, we have seen that aggregates of 
