d
were of a totally different character from the scales of ordinary
fishes. These conclusions are as certain as any based upon probable
reasonings can be. And they are so, simply because a very large
experience justifies us in believing that teeth of this particular form
and structure are invariably associated with the peculiar organisation
of sharks, and are never found in connection with other organisms. Why
this should be we are not at present in a position even to imagine; we
must take the fact as an empirical law of animal morphology, the reason
of which may possibly be one day found in the history of the evolution
of the shark tribe, but for which it is hopeless to seek for an
explanation in ordinary physiological reasonings. Every one practically
acquainted with palaeontology is aware that it is not every tooth, nor
every bone, which enables us to form a judgment of the character of the
animal to which it belonged; and that it is possible to possess many
teeth, and even a large portion of the skeleton of an extinct animal,
and yet be unable to reconstruct its skull or its limbs. It is only
when the tooth or bone presents peculiarities, which we know by previous
experience to be characteristic of a certain group, that we can safely
predict that the fossil belonged to an animal of the same group. Any one
who finds a cow's grinder may be perfectly sure that it belonged to an
animal which had two complete toes on each foot and ruminated; any one
who finds a horse's grinder may be as sure that it had one complete
toe on each foot and did not ruminate; but if ruminants and horses
were extinct animals of which nothing but the grinders had ever been
discovered, no amount of physiological reasoning could have enabled
us to reconstruct either animal, still less to have divined the
wide differences between the two. Cuvier, in the "Discours sur les
Revolutions de la Surface du Globe," strangely credits himself, and has
ever since been credited by others, with the invention of a new method
of palaeontological research. But if you will turn to the "Recherches
sur les Ossemens Fossiles" and watch Cuvier, not speculating, but
working, you will find that his method is neither more nor less than
that of Steno. If he was able to make his famous prophecy from the jaw
which lay upon the surface of a block of stone to the pelvis of the same
animal which lay hidden in it, it was not because either he, or any
one else, knew, or knows, wh