On the Genesis of Species

Africa and India; to Africa and South America; to China and Australia; to North America and China; to New Zealand and South America; to South America and Tasmania; to South Am

es of accounting for facts of distribution.-Indepe

tended that such facts do by any means constitute by themselves obstacles which cannot be got over. Indeed it would be difficult to imagine any obstacles of the kind which could not be surmounted by an indefinite number of terrestrial modifications of surface-submergences and emergences-junctions and separations of continents

nnected with the geographical distribution of animals are not without significance, and are worthy of mention even though, by themselves, they constitu

cable by the hypothesis of slight elevations and depressions of larger and smaller parts of it

es,[142] "In regard to fish, I believe that the same species never occur in the fresh waters of distant continents." Now, the Author is enabled, by the labours and through the kindness of Dr. Günther, to show that this belief cannot be maintained; he having been so obliging as to call attention to the following facts with regard to f

d, to Aleppo on the other. Nevertheless, a new species (M. cryptacanthus) has been described by the same author,[144] which is an inhabitant of the Camaroon country of Western Africa. He observes, "The occurr

y-five species,[145] all from the fresh waters of the East Indies. Yet Dr. Gü

nine freshwater genera, and these are distributed

nd in India, Africa, and Madagascar,

ate connexion between Africa and India, harmonizing

nd in Africa and South America, and not in India, and even its component groups

na in that almost exclusively

a, and Australia, and the species P. anguillaris[150] has been brought from both China and Moreton Bay. Here, therefore, we have the

s from India. On the other hand, Amiurus is a North American

ommon to South America and Tasmania. In this genus we thus have an absolutely and completely fresh-

other form of the same family, namely, Geotria chilensis,[155] is found not only in South America and

t continents, although it cannot be certainly affirmed that they are exclusively and

ca, Australia, Tasmania, and New Zealand on the other; but these unions were not synchronous any more than the

of the margin of the jaw. Now pleurodont iguanian lizards abound in the South American region; but nowhere else, and are not as yet known to inhabit any part of the present continent of Africa. Yet pleurodo

OWER JAW OF PLE

ttached to the inner

olenodon, which is a resident in the West Indian 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

and toads which respectively inhabit those regions. A truly remarkable similarity and parallelism exist, however, between certain of the same animals inhabiting

ENO

South America, New Zealand, and Austra

ance 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, T

ally across the equator, and thus account, amongst other things, for the appearance in Chile of frogs having close genetic relations with European forms. But it is difficult to understand the persisten

, 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 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 for thinking that a southern continent, rich in living forms, once existed. One such

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 conte

has 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-forme

ase 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 inter

-if, especially, there is reason to believe that geological time has not been sufficient for it, then it will be well to bear in mind the facts here enumerated. These facts, however, are not opposed to the