The

wonderfully folded teeth of the labyrinthodonts. marvellously complex structure of these organs is not merely unaccountable as due to "Natural Selection," but its production by insignificant increments of complexity is hardly less difficult to comprehend.

Similarly the aborted index of the Potto (Perodicticus) is a structure not likely to have been induced by minute changes; while, as to "Natural Selection," the reduction of the forefinger to a mere rudiment is inexplicable indeed! "How this mutilation can have aided in the struggle for life, we must confess, baffles our conjectures on the sub

ject; for that any very appreciable gain to the individual can have resulted from the slightly lessened degree of required nourishment thence resulting (i.e. from the suppression), seems to us to be an almost absurd proposition." 1

Again to anticipate somewhat, the great group of whales (Cetacea) was fully developed at the deposition of the Eocene strata. On the other hand, we may pretty safely conclude that these animals were absent as late as the latest secondary rocks, so that their development could not have been so very slow, unless geological time is (although we shall presently see there are grounds to believe it is not) practically infinite. It is true that it is generally very unsafe to infer the absence of any animal forms during a certain geological period because no remains of them have as yet been found in the strata then deposited: but in the case of the Cetacea it is safe to do so; for, as Sir Charles Lyell remarks,2 they are animals the remains of which are singularly likely to have been preserved had they existed, in the same way

1 "Anatomy of the Lemuroidea." By James Murie, M.D., and St. George Mivart. Trans. Zool. Soc., March 1866, p. 91.

2 66

Principles of Geology," last edition, vol. i. p. 163.

that the remains were preserved of the Ichthyosauri and Plesiosauri, which appear to have represented the Cetacea during the secondary geological period.

SKELETON OF A PLESIOSAURUS.

As another example let us consider the origin of wings, as they exist in birds. Here we find in fact an arm, the bones of the hand of which are atrophied and reduced in number, as compared with those of most other Vertebrates. Now, if the wing took its origin from a terrestrial or subaërial organ, this abortion of the bones could hardly have been serviceable hardly have preserved individuals in the struggle for life. If it arose from an aquatic organ, like

the wing of the penguin, we have then a singular divergence from the ordinary vertebrate fin-limb. In the ichthyosaurus, in the plesiosaurus, in the whales, in the porpoises, in the seals, and in others, we have shortening of the bones, but no reduction in the number either of the fingers or of their joints, which are, on the contrary, multiplied in Cetacea and the ichthyosaurus. And even in the

turtles we have eight carpal bones and five digits, while no finger has less than two phalanges. It is difficult, then, to believe that the Avian limb was developed in any other way than by a comparatively sudden modification of a marked and important kind.

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,1 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."

"2

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-aye3 (Chiromys Madagas

1 Quarterly Journal of Science, April 1866, pp. 257–8. 2"Habit and Intelligence," vol. i. p. 178.

3 This animal belongs to the order Primates, which includes man, the apes, and the lemurs. The lemurs are the lowest kinds of the order, and differ much from the apes. They have their head-quarters in the Island of Madagascar. The aye-aye is a lemur, but it differs singularly from all its congeners, and still more from all apes. In its dentition it strongly approximates to the rodent (rat, squirrel, and guinea-pig) order, as it has two cutting teeth above, and two below, growing from permanent pulps, and in the adult condition has no canines.

cariensis) 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 which has now been made demonstrates that it has no more essential affinity to rodents than any other lemurine creature has.

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.

In the same way it has been till 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 already said, it is contended that not only had they no such close affinity, but that other extinct reptiles had a far closer one.