Lion and Leopard, are copied so to speak by the Puma and Jaguar of tropical America; the Tapir of Mexico mimics the congeneric animal of Sumatra a; the Sloth, Armadillo, and Myrmecophaga of Brazil, find relatives in the Manis and Orycteropus of Asia and Africa.

These parallels might be extended by many examples from Struthious and other birds, and from Crocodiles and other reptiles, tending to shew in two large separated regions, two distinct but analogous groups of life, subject to similar limitations by climate.

In like manner, reef-making Corals in the sea, and the large molluscous families of Cones, Cowries, and Volutes, might be mentioned as characterizing the warmer waters; but a more curious and interesting law of distribution of marine life, is founded on investigation of the contents of the sea at different depths.

INFLUENCE OF DEPTH ON THE DISTRIBUTION OF LIFE IN THE SEA.

One example, the best known, is the Survey of the Ægean sea-depths by the late excellent naturalist, Edward Forbes. Dividing the depths from the surface to 230 fathoms into eight unequal zones, he finds

The first column gives the zones in succession downwards.

The second gives the limits of the zone in depth by fathoms.

The third, the depth in thickness of each zone in fathoms.

The fourth the number of species found in each

zone.

The fifth is a column which I have calculated by dividing the fourth by the third, to shew the relative productiveness of each zone. (For the sake of avoiding decimals, the quotient is multiplied by 10.)

Thus it appears that the relative fertility of the several zones decreases downwards toward zero: and it is believed that at 300 fathoms life is extinct.

If we consider that at and near the surface of the sea all the influences favourable to both vegetable

and animal life must have their greatest effect, here being the greatest mixture of air with the water; the greatest motion of the water, to give full effect to that mixture; the greatest amount of stimulating light, and the greatest change of daily temperature; we shall readily conceive that near the surface the forms of life should be both more varied and more abundant; while, on the other hand, in the deeper and calmer water, less light, less motion, less air and less change of air, should correspond to fewer and less varied inhabitants. Only a few of the Mollusca are, like the Argonaut of the Poet, who tilts along the Atlantic waves

But if a breath of danger sound,

With sails quick-furled she dives profound,
And far below the tempest's path

In coral grots defies the foe,

That never broke, in heaviest wrath,

The sabbath of the deeps below.

In a Diagram, Fig. 2, we may represent the limits of life above and below the level of the sea by setting off on the vertical line a scale of heights and depths, and drawing at right angles to this, for each selected zone of height and depth, lines representing the ratios of abundance of life. Thus shall we have, in a general form, an expression of the apparent dependence of life on elevation above and depression below the general level of the surface of the sea. The real dependence on the land is

R. L.

C