l and internal, in
such diverse ways and proportions that the results (unequals being added to
unequals) shall be equal and similar. Still, though highly improbable, this
cannot be said to be impossible; and if there _is_ an innate law of any
kind helping to determine specific evolution, this may more or less, or
entirely, neutralize or even reverse the effect of ancestral habit. Thus,
it is quite conceivable that a pleurodont lizard might have arisen in
Madagascar in perfect independence of the similarly-formed American
lacertilia: just as certain teeth of carnivorous and insectivorous
marsupial animals have been seen most closely to resemble those of
carnivorous and insectivorous placental beasts; just as, again, the paddles
of the Cetacea resemble, in the fact of a multiplication in the number of
the phalanges, the many-jointed feet of extinct marine reptiles, and as the
beak of the cuttle-fish or of the tadpole resembles that of birds. We have
already seen (in Chapter III.) that it is impossible, upon any hypothesis,
to escape admitting the independent origins of closely similar forms, It
may be that they are both more frequent and more important than is
generally thought.

That closely similar structures may arise without a genetic relationship
has been lately well urged by Mr. Ray Lankester.[159] He has brought {153}
this notion forward even as regards the bones of the skull in osseous
fishes and in mammals. He has done so on the ground that the probable
common ancestor of mammals and of osseous fishes was a vertebrate animal of
so low a type that it could not be supposed to have possessed a skull
differentiated into distinct bony elements--even if it was bony at all. If
this was so, then the cranial bones must have had an independent origin in
each class, and in this case we have the most strikingly harmonious and
parallel results from independent actions. For the bones of the skull in an
osseous fish are so closely conformed to those of a mammal, that "both
types of skull exhibit many bones in common," though "in each type some of
these bones acquire special arrangements and very different
magnitudes."[160] And no investigator of homologies doubts that a
considerable number of the bones which form the skull of any osseous fish
are distinctly homologous with the cranial bones of man. The occipital, the
parietal, and frontal, the bones which surround the internal ear, the
vomer, the premaxilla, and the quadrate bo