Madagascar. This is the more remarkable, as we have no evidence yet of the existence in Madagascar of fresh-water fishes common to Africa and South America.

Again, that interesting island Madagascar is the home of very singular and special insectivorous beasts of the genera Centetes, Ericulus, and Echinops; while the only other member of the group to which they belong is Solenodon, which is a resident in the West India Islands,

Cuba and Hayti. The connexion, however, between the West Indies and Madagascar must surely have been at a time when the great lemurine group was absent; for it is difficult to understand the spread of such a form as Solenodon, and at the same time the non-extension of the active lemurs, or their utter extirpation, in such a congenial situation as the West Indian Archipelago.

The close connexion of South America and Australia is demonstrated (on the Darwinian theory), not only from the marsupial fauna of both, but also from the frogs and toads which respectively inhabit those regions. A truly remarkable similarity and parallelism exist, however, between certain of the same animals inhabiting SouthWestern America and Europe. Thus Dr. Günther has described a frog from Chile by the name of cacotus, which singularly resembles the European bombinator.

Again of the salmons, two genera from South America, New Zealand, and Australia, are analogous to European salmons.

In addition to this may be mentioned a quotation from Professor Dana, given by Mr. Darwin,2 to the effect that "it is certainly a wonderful fact that New Zealand should have a closer resemblance in its crustacea to Great Britain, its antipode, than to any other part of the world:" and Mr. Darwin adds, "Sir J. Richardson also speaks of the reappearance on the shores of New Zealand, Tasmania, &c., of northern forms of fish. Dr. Hooker informs me that twenty-five species of algae are common to New Zealand and to Europe, but have not been found in the intermediate tropical seas."

Many more examples of the kind could easily, be brought forward, but these may suffice. As to the last-mentioned cases, Mr. Darwin explains them by the influence of the glacial epoch, which influence he would extend actually across the equator,3 and thus account for, amongst other 1 Proc. Zool. Soc. 1868, p. 482.

2 "Origin of Species," 5th edition, 1869, p. 454.

3 Mr. J. J. Murphy, in a very interesting paper read before the Geological Society, June 9th, 1869, advances weighty reasons for believing that "the equatorial regions were never glaciated at all” (p. 355).

matters, the appearance in Chile of frogs having close genetic relations with European forms. But it is difficult to understand the persistence and preservation of such exceptional forms with the extirpation of all the others which probably accompanied them, if so great a migration of northern kinds had been occasioned by the cold of the glacial epoch.

1

Mr. Darwin candidly says, "I am far from supposing that all difficulties in regard to the distribution and affinities of the identical and allied species, which now live so widely separated in the north and south, and sometimes on the intermediate mountain-ranges, are removed."

"We cannot say why certain species and not others have migrated; why certain species have been modified and have given rise to new forms, whilst others have remained unaltered." Again he adds, "Various difficulties also remain to be solved; for instance, the occurrence, as shown by Dr. Hooker, of the same plants at points so enormously remote as Kerguelen Land, New Zealand, and Fuegia; but icebergs, as suggested by Lyell, may have been concerned in their dispersal. The existence, at these and other distant points of the southern hemisphere, of species which, though distinct, belong to a genera exclusively confined to the south, is a more remarkable case. Some of these species are so distinct that we cannot suppose that there has been time since the commencement of the last glacial period for their migration and subsequent modification to the necessary degree." Mr. Darwin goes on to account for these facts by the probable existence of a rich antarctic flora in a warm period anterior to the last glacial epoch. There are indeed many reasons 1 "Origin of Species," 5th edition, p. 459.

for thinking that a southern continent, rich in living forms, once existed. Among these reasons is the distribution of struthious birds around the antarctic region as the ostrich in Africa, the rhea in South America, the emeu in Australia, the apteryx, dinornis, &c. in New Zealand, the epiornis in Madagascar. Still the existence of such a land would not alone explain the various geographical cross relations which have been given above. It would not, for example, account for the resemblance between the crustacea or fishes of New Zealand and of England. It would, however, go far to explain the identity (specific or generic) between fresh-water and other forms now simultaneously existing in Australia and South America, or in either or both of these, and New Zealand.

Again, mutations of elevation small and gradual (but frequent and intermitting), through enormous periods of time-waves, as it were, of land rolling many times in many directions-might be made to explain numerous difficulties as to geographical distribution, and any cases that remained would probably be capable of explanation, as being isolated but allied animal forms, now separated indeed, but being merely remnants of extensive groups which, at an earlier period, were spread over the surface of the earth. Thus none of the facts here given are any serious difficulty to the doctrine of "evolution;" but it is contended in this book that if other considerations render it improbable that the manifestation of the successive forms of life has been brought about by minute, indefinite, and fortuitous variations, then these facts as to geographical distribution intensify that improbability, and are so far worthy of attention.

All geographical difficulties of the kind would be evaded

if we could concede the probability of the independent origin, in different situations, of the same organic forms in animals high in the scale of nature. Similar causes must produce similar results, and new reasons have been lately adduced for believing, as regards the lowest organisms, that the same forms can arise and manifest themselves independently. The difficulty as to higher animals is, however, much greater, as (on the theory of evolution) one acting force must always be the ancestral influences in each case, and this force must always tend to go on acting in the same groove and direction in the future as it has done in the past. So that it is difficult to conceive that individuals the ancestral history of which is very different, can be acted upon by all influences, external 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