in the independent development of two closely similar forms. In all cases, no doubt (on this same theory), some adaptation to habit or need would gradually be evolved, but that adaptation would surely be arrived at by different roads.

The organic world supplies us with multitudes of examples of similar functional results being attained by the most diverse means. Thus the body is sustained in the air

by birds and by bats. In the first case it is so sustained by a limb in which the bones of the hand are excessively reduced, but which is provided with immense outgrowths

DAE

WING-BONES OF PTERODACTYLE, BAT, AND BIRD.

from the skin-namely, the feathers of the wing. In the second case, however, the body is sustained in the air by a limb in which the bones of the hand are enormously increased in length, and so sustain a great expanse of naked skin, which is the flying membrane of the bat's wing. Certain fishes and certain reptiles can also flit and take very prolonged jumps in the air. The flying-fish, however takes these by means of a great elongation of the rays of

the pectoral fins-parts which cannot be said to be of the same nature as the constituents of the wing of either the bat or the bird. The little lizard, which enjoys the formidable name of "flying-dragon," flits by means of a structure altogether peculiar-namely, by the liberation and great elongation of some of the ribs which support a fold of skin. In the extinct pterodactyles-which were truly flying rep

tiles-we meet with an approximation to the structure of the bat, but in the pterodactyle we have only one finger elongated in each hand: a striking example of how the very same function may be provided for by a modification similar in principle, yet surely manifesting the independence of its origin. When we go to lower animals, we find flight produced by organs, as the wings of insects, which are not

modified limbs at all; or we may even find the function subserved by quite artificial means, as in the aërial spiders, which use their own threads to float with in the air. In the vegetable kingdom the atmosphere is often made use of for the scattering of seeds, by their being furnished with special structures of very different kinds. The various modes by which such seeds are dispersed are well expressed by Mr. Darwin. He says:1 "Seeds are disseminated by their minuteness, by their capsule being converted into a light balloon-like envelope, -by being embedded in pulp or flesh, formed of the most diverse parts, and rendered nutritious, as well as conspicuously coloured, so as to attract and be devoured by birds,—by having hooks and grapnels of many kinds and serrated awns, so as to adhere to the fur of quadrupeds,—and by being furnished with wings and plumes, as different in shape as elegant in structure, so as to be wafted by every breeze."

Again, if we consider the poisoning apparatus possessed by different animals, we find in serpents a perforated-or rather very deeply channelled-tooth. In wasps and bees the sting is formed of modified parts, accessory in reproduction. In the scorpion, we have the median terminal process of the body specially organized. In the spider, we have a specially constructed antenna; and finally, in the centipede a pair of modified thoracic limbs.

It would be easy to produce a multitude of such instances of similar ends being attained by dissimilar means, and it is here contended that by "the action of Natural Selection" only it is so improbable as to be practically impossible for two exactly similar structures to have ever been indepen"Origin of Species," 5th edition, p. 235.

dently developed. It is so because the number of possible variations is indefinitely great, and it is therefore an indefinitely great number to one against a similar series of variations occurring and being similarly preserved in any two independent instances.

The difficulty here asserted applies exclusively, however, to pure Darwinism, which makes use only of indirect modifications through the survival of the fittest.

Other theories (for example, that of Mr. Herbert Spencer) admit the direct action of conditions upon animals and plants-in ways not yet fully understood-there being conceived to be at the same time a certain peculiar but limited power of response and adaptation in each animal and plant so acted on. Such theories have not to contend against the difficulty proposed, and it is here urged that even very complex extremely similar structures have again and again been developed quite independently one of the other, and this because the process has taken place not by merely haphazard, indefinite variations in all directions, but by the

concurrence of some other and internal natural law or laws co-operating with external influences and with "Natural Selection" in the evolution of organic forms.

It must never be forgotten that to admit any such constant operation of any such unknown natural cause is to deny the purely Darwinian theory, which relies upon the survival of the fittest by means of minute fortuitous indefinite variations.

Amongst many other obligations which the author has to acknowledge to Professor Huxley, are the pointing out of this very difficulty, and the calling his attention to the striking resemblance between certain teeth of the dog and of the thylacine as one instance, and certain ornithic peculiarities of pterodactyles as another.

Mammals 1 are divisible into one great group, which comprises the immense majority of kinds termed, from their mode of reproduction, placental Mammals, and into another very much smaller group, comprising the pouchedbeasts or marsupials (which are the kangeroos, bandicoots, phalangers, &c., of Australia, and the true opossums of America), called implacental Mammals. Now the placental mammals are subdivided into various orders, amongst which are the flesh-eaters (Carnivora, i.e. cats, dogs, otters, weasels, &c.), and the insect-eaters (Insectivora, i.e. moles, hedgehogs, shrew-mice, &c.). The marsupial mammals also present a variety of species (some of which are carnivorous, whilst others are insectivorous), so varied in form that it has been even proposed to group them into orders parallel to the orders of placental beasts.

1 I.e. warm-blooded animals which suckle their young, such as apes, bats, hoofed beasts, lions, dogs, bears, weasels, rats, squirrels, armadillos, sloths, whales, porpoises, kangaroos, opossums, &c.