ntion to the resemblance
between the anterior molars of the placental dog with those of the
marsupial thylacine. These, indeed, are strikingly similar, but there are
better examples still of this sort of coincidence. Thus it has often {69}
been remarked that the insectivorous marsupials, _e.g. Perameles_,
wonderfully correspond, as to the form of certain of the grinding teeth,
with certain insectivorous placentals, _e.g. Urotrichus_.

Again, the saltatory insectivores of Africa (_Macroscelides_) not only
resemble the kangaroo family (_Macropodidae_) in their jumping habits and
long hind legs, but also in the structure of their molar teeth, and even
further, as I have elsewhere[52] pointed out, in a certain similarity of
the upper cutting teeth, or incisors.

Now these correspondences are the more striking when we bear in mind that a
similar dentition is often put to very different uses. The food of
different kinds of apes is very different, yet how uniform is their dental
structure! Again, who, looking at the teeth of different kinds of bears,
would ever suspect that one kind was frugivorous, and another a devourer
exclusively of animal food?

The suggestion made by Professor Huxley was therefore one which had much to
recommend it to Darwinians, though it has not met with any notable
acceptance, and though he seems himself to have returned to the older
notion, namely, that the pouched-beasts, or marsupials, are a special
ancient offshoot from the great mammalian class.

But whichever view may be the correct one, we have in either case a number
of forms similarly modified in harmony with surrounding conditions, and
eloquently proclaiming some natural plastic power, other than mere
fortuitous variation with survival of the fittest. If, however, the Reader
thinks that teeth are parts peculiarly qualified for rapid variation (in
which view the Author cannot concur), he is requested to suspend his
judgment till he has considered the question of the independent evolution
of the _highest organs of sense_. If this seems to establish the {70}
existence of some other law than that of "Natural Selection," then the
operation of that other law may surely be also traced in the harmonious
co-ordinations of dental form.

The other difficulty, kindly suggested to me by the learned Professor,
refers to the structure of birds, and of extinct reptiles more or less
related to them.

The class of birds is one which is remarkabl