'succession' of their constituents, of which I shall speak
afterwards--differ from the 'Flora' and 'Fauna' of the present
day;--how far they differ in what we 'do' know about them, leaving
altogether out of consideration speculations based upon what we 'do
not' know.

I strongly imagine that if it were not for the peculiar appearance that
fossilised animals have, any of you might readily walk through a museum
which contains fossil remains mixed up with those of the present forms
of life, and I doubt very much whether your uninstructed eyes would
lead you to see any vast or wonderful difference between the two. If
you looked closely, you would notice, in the first place, a great many
things very like animals with which you are acquainted now: you would
see differences of shape and proportion, but on the whole a close
similarity.

I explained what I meant by ORDERS the other day, when I described the
animal kingdom as being divided in sub-kingdoms, classes and orders. If
you divide the animal kingdom into orders, you will find that there are
about one hundred and twenty. The number may vary on one side or the
other, but this is a fair estimate. That is the sum total of the orders
of all the animals which we know now, and which have been known in past
times, and left remains behind.

Now, how many of those are absolutely extinct? That is to say, how many
of these orders of animals have lived at a former period of the world's
history, but have at present no representatives? That is the sense in
which I meant to use the word "extinct." I mean that those animals did
live on this earth at one time, but have left no one of their kind with
us at the present moment. So that estimating the number of extinct