t responsible. I mean that the
framing of this natural classification has been the work of naturalists
for centuries past; and although they did not know what they were doing,
it is now evident to evolutionists that they were tracing the lines of
genetic relationship. For, be it observed, a scientific or natural
classification differs very much from a popular or hap-hazard
classification, and the difference consists in this, that while a
popular classification is framed with exclusive reference to the
external appearance of organisms, a scientific classification is made
with reference to the whole structure. A whale, for instance, is often
thought to be a fish, because it resembles a fish in form and habits;
whereas dissection shows that it is beyond all comparison more unlike a
fish than it is like a horse or a man. This is, of course, an extreme
case; but it was cases such as this that first led naturalists to see
that there are resemblances between organisms much more deep and
important than appear upon the surface; and consequently, that if a
natural classification was possible at all, it must be made with
reference to these deeper resemblances. Of course, it took time to
perceive this distinction between fundamental and superficial
resemblances. I remember once reading a very comical disquisition in one
of Buffon's works on the question as to whether or not a crocodile was
to be classified as an insect; and the instructive feature in the
disquisition was this, that although a crocodile differs from an insect
as regards every conceivable particular of its internal anatomy, no
allusion at all is made to this fact, while the whole discussion is made
to turn on the hardness of the external casing of a crocodile resembling
the hardness of the external casing of a beetle; and when at last Buffon
decides that, on the whole, a crocodile had better not be classified as
an insect, the only reason given is, that as a crocodile is so very
large an animal, it would make "altogether too terrible an insect."

But now, when at last it came to be recognised that internal anatomy
rather than external appearance was to be taken as a guide to
classification, the question was, What features in the internal anatomy
are to take precedence over the other features? And this question it was
not hard to answer. A porpoise, for instance, has a large number of
teeth, and in this feature resembles most fish, while it differs from
all mammals. B