aratively sudden modification of a marked and
important kind.

[Illustration: SKELETON OF AN ICHTHYOSAURUS.]

How, once more, can we conceive the peculiar actions of the tendrils of
some climbing plants to have been produced by minute modifications? These,
according to Mr. Darwin,[101] oscillate till they touch an object, and then
embrace it. It is stated by that observer, "that a thread weighing no more
than the thirty-second of a grain, if placed on the tendril of the
_Passiflora gracilis_, will cause it to bend; and merely to touch the
tendril with a twig causes it to bend; but if the twig is at once removed,
the tendril soon straightens itself. But the contact of other tendrils of
the plant, or of the falling of drops of rain, do not produce these
effects."[102] But some of the zoological and anatomical discoveries of
late years tend rather to diminish than to augment the evidence in favour
of minute and gradual modification. Thus all naturalists now admit that
certain animals, which were at one time supposed to be connecting links
between groups, belong altogether to one group, and not at all to the
other. For example, the aye-aye[103] (_Chiromys Madagascariensis_). {108}
was till lately considered to be allied to the squirrels, and was often
classed with them in the rodent order, principally on account of its
dentition; at the same time that its affinities to the lemurs and apes were
admitted. The thorough investigation into its anatomy that has now been
made, demonstrates that it has no more essential affinity to rodents than
any other lemurine creature has.

[Illustration: THE AYE-AYE.]

Bats were, by the earliest observers, naturally supposed to have a close
relationship to birds, and cetaceans to fishes. It is almost superfluous to
observe that all now agree that these mammals make not even an approach to
either one or other of the two inferior classes.

{109}
In the same way it has been recently supposed that those extinct flying
saurians, the pterodactyles, had an affinity with birds more marked than
any other known animals. Now, however, as has been said earlier, it is
contended that not only had they no such close affinity, but that other
extinct reptiles had a far closer one.

The _amphibia_ (_i.e._ frogs, toads, and efts) were long considered (and
are so still by some) to be reptiles, showing an affinity to fishes. It now
appea