Setting aside the marsupials and edentata, to which we shall return, it is true that the great normal orders of terrestrial mammals, the ruminants, rodents, insectivora, and carnivora are almost as cosmopolitan as man. But this is no longer the case with the cheiroptera, not one of which passes the polar circle. As to the quadrumana, it is well-known that they are wanting in Europe, with the exception of the Rock of Gibraltar, in North America and in the greater part of Asia and Oceania. Thus it appears that, even in the extreme hypothesis which I have here indicated, it would not be in the animal types which present the greatest resemblance to man, but among the carnivora or ruminants that we should be forced to seek for geographical analogies in favour of the pretended cosmopolitanism of the _human order_. V. This limitation of the areas of habitation of animals, which is evidently related to their degree of elevation in the scale of beings, is a general fact which we also meet with in plants. On this point Ad. de Candolle speaks as follows:—“The mean area of species is smaller according as the class to which they belong has a more complete, a more highly developed, or, in other words, a more perfect organisation.” The _progressive localisation_ of organised beings, increasing in degree as they become more perfect, is, then, a general law. Physiology will readily account for this fact. The perfection of organisms is the result of division of labour, which demands the multiplication of functional apparatus. As the anatomical instruments become more numerous and special, the functions do the same. From this cause alone the conditions of harmony between the living being and the conditions of life which surround it become more and more definite. Consequently, the animal or the plant only finds its really favourable conditions in a constantly diminishing area. Beyond these limits the conditions of life change, the struggle for existence becomes more hazardous, and the spread of the species, genus, family, or even order is arrested. Man alone, armed against the conditions of life by his _intelligence_ and _industry_, is capable of overcoming conditions of existence which would be an impassable barrier _to his material organisation_. The law of progressive localisation is in direct opposition to the doctrine of the original cosmopolitanism of the human species. In putting it aside, polygenists, properly so called, might draw attention to the diffusion of the genera of dolphins and rorquals; polygenistic monogenists of the school of Agassiz might argue from the facts mentioned above in connection with the genera of megaptera and sibaldius; they might both say: The general law of localisation offers two exceptions; why should not man form a third?