and yield oxygen in return; while on the other hand, animals inspire this oxygen, and evolve in exchange carbonic acid. Thus appears a real and necessary relation between the atmosphere as it is, and the double system of life which is in operation. If we change the constitution of the atmosphere, all the relations in which it is so important must be changed also, and amongst the most obvious of these are the reciprocally dependent races of plants and animals. It has been conjectured by Brongniart, that the very rich series of vegetable forms, including many ferns, in the old carboniferous deposits, may have been favoured in their amazing growth, not only by high temperature and humid atmosphere, but by a greater proportion of carbonic acid in the air. Dr Daubeny has submitted this to a trial, in vessels properly supplied with a regulated artificial atmosphere, and the result is not unfavourable to the speculation.

Again, animal life depends upon the previous exercise of vegetable life; for ultimately all animals subsist upon plants, as these feed upon the atmosphere. Perhaps nothing is more surprising than the immense diversity of the forms and qualities of the plants, coupled with the almost equal dependence of all vegetative life upon the same atmosphere chemically everywhere almost identical. Upon this

vast variety of plants, innumerable hosts of herbivorous animals feed, and they minister to the appetites of the Carnivora. It is conceivable that while the plants remain unchanged, the Herbivora might vary, or might become the prey of different flesheaters; but it is perhaps not conceivable that with such an atmosphere as ours, under such conditions as now obtain, there could be generally any great variation in the relative total amount of vital energy in plants, compared with animals. There seems also a high degree of permanence in the relation of Herbivora compared with Carnivora. Our marine Cetacea might be replaced by Enaliosaurians; our Gasteropoda by Crustacea; our fishes by Cephalopoda; but the researches of geology seem to shew that from the earliest periods, carnivora and herbivora, plants and animals, have been combined into the same general relations of mutual dependence as at present.

Subject to these conditions, life appears in all the habitable spaces of the land, sea and air, filling each with beings capable of enjoying their own existence, and of ministering to the bodily wants and intellectual longings of the one observing and reflecting being to whom God has committed the wonderful gift of thoughts which reach back beyond the origin of his race, and stretch forward to a brighter futurity.

In the elements of land, air, and water, both plants and animals are fitted to live by means of contrivances varied in almost every individual case, but always to be conceived of as elegant adaptations to some conditions of matter-adaptations to gravity, to force of wind, to depth of water, to degrees of light, to periodicity of seasons, and even to local and limited occurrences. Regard the eye which in its perfect state, as in man, is destined to feel the presence or absence of light, to distinguish the colours of the several rays, and to perceive the forms of the luminous surfaces. What is it but a triple photographic lens with six curved surfaces calculated for three different media; calculated for achromaticity and spherical aberration ; provided with a variable self-adjusting aperture, and a variable self-adjusting focal length, adapted to something better and more sensitive than a collodionplate-the beautifully expanded and guarded retina, which after the fraction of a second of time is ready to receive a new impression with undiminished energy. Regard the two eyes, the natural stereoscope, by whose beautiful joint action solids take their proper aspect, distance is estimated, and the landscape acquires that instructive composition which our artists delight to imitate.

Again, regard this wonderful organ, modified to

suit the sunny flight of the eagle, the twilight mousing of the owl, the brousing of the ruminant, the nocturnal watch of the lion; the watery life of the whale, or the fish, where the different refractive power of the fluid in which they live is accompanied by modifications, not alike in each, but yet alike in the manifestation of intentional adaptation. Consider in the same point of view the large orbit of Ichthyosaurus with its broad circlet of sclerotic bones; or the reticulated lenses of the Trilobite; or finally, the black or red spots sensitive only to light in the Mollusca and Radiata; or scrutinize in the same way any other organ of sense, in the animals of every age, and inquire with the Psalmist:

He who planted the ear, shall He not hear?

He who made the eye, shall He not see?

Life runs always the same course of growth, decay and death, in the individual-always the same course of renewal by offspring, after a definite mode which varies with the different kinds of living beings. One of these modes seems to deserve separation from the rest, under the title of fissiparism, because in it the individual seems divided, and so the number of individuals multiplied. This obtains among the Polyparian Zoophyta, and may be paralleled among many plants, and artificially exemplified by cuttings.

But in general, there is the preparation of egg or seed, the development of these in connection with nutritive matter prepared in each, and the passage through several stages before the complete state of individual life is attained; then recurs the separation of parts impressed with the wonderful power, and subject to the inconceivable restraint, of so acting on and being acted on by the elementary powers around, as to grow, reproduce and decay, in forms and through periods corresponding to those appointed for their ancestral races since time began.

INFLUENCE OF CLIMATE ON THE DISTRIBUTION OF LIFE.

Not the whole surface of the earth is occupied by living beings. Notwithstanding the perpetual struggle to diffuse their seed, plants do not cover all the regions of the land; nor is the amazing fertility of many marine animals able to carry life into all parts of the sea. The geographical distribution of plants and animals, a subject of great richness and instruction, offers some general facts which must not be neglected in reasoning on the ancient forms of life which fill the stratified rocks.

Among the most influential of all the causes which limit the ranges of life is temperature. The