Peter Parley's Wonders of the Earth, Sea, and Sky

by Samuel G. Goodrich

V. You may see that there is, in every variety of circumstance, something that enjoys itself, and has a place to fill up and a part to act amongst the creatures which God has made. But this is not all: the existence of the cold of the Poles, and of the heat of the Tropics, is necessary to the well-being of the whole.

The free air that surrounds the globe, which we breathe, and through which we see, and hear, and smell, and move, is the same in composition in every part of the world. It contains just the same proportions of the two gases, oxygen and nitrogen, in the coldest and the hottest climates, in the deepest valleys and on the tallest mountains. Now, this air, considered on a large scale, is always blowing from the Poles towards the Equator. The more direct rays of the sun heat that portion of the earth's surface which lies in the Torrid Zone, and therefore the air above it is perpetually ascending to the upper regions of the atmosphere, to make room for that which presses upon it from the Poles, because it is cooler and heavier.

It is this process, united with the motion of the earth on its axis, which causes the Trade Winds and Monsoons.

Now, do you not see how necessary the cold Poles are to keep the rest of the world from becoming too hot, by supplying constant currents of fresh air setting in upon the hotter regions from both sides? Then the air, which ascends from the Equator, becomes cool, and travels down again to join the air from the Poles; and so a healthful circulation is kept up, which is necessary for all climates.

VI. It is very interesting to trace the dependance of the various tribes of vegetables and animals on each other, and to observe how one flourishes through the dissolution of another; and still more so to notice the gradual development of the same parts in the kinds, as they ascend one above another. You may see an instance of this in three of the animals that I described to you, which were different enough in other respects, but agreed in being without a bony skeleton, and in having long organs round their mouths to catch their food with.

In the Acalephæ, or sea-nettles, these organs were merely filaments without sensation, of which the use seemed to be, to entangle little creatures in, which chance might bring in their way. The animals themselves would seem, at first sight, to be very ill able to destroy small crabs and other shell-fish. You would suppose that the struggles they would make with their hard pointed legs, would tear the tender bodies of the Acalephæ; but the deficiency is supplied by the caustic luminous fluid which paralyzes the victim, and disables it for violent struggles while it is detained by the filaments, before the Acalepha attempts to swallow it.

In the Actiniæ, you will find the loose disorderly filaments changed into feelers, with wonderfully acute sensation, regularly disposed in a star. When a substance touches the feelers they close in with considerable power, but seem to act more like a mechanical trap,—as the leaves of certain plants catch flies and other insects,—than in direct dependance on the will of the animal. However, the Actinia has the sense of feeling, and has a perception of light and of odours, though without eyes or nose. Having greater muscular strength and more compactures of film, he does not need the destructive fluid with which the Acalepha is furnished. Thus, one sort of power is made to compensate for the loss of another.

The Sepia also catches his food by means of fleshy organs placed round his mouth; but in him you find them possessed of amazing power, moving in strict subjection to his will; never loosely floating about as in the others. Then he tastes, sees, and hears, by means of a tongue, eyes, and ears, distinctly formed.

A similar gradation is observed in the development of the various parts composing the hand and arm in animals with perfect skeletons, in which the bones act as levers. There is a very interesting book[C] written on this subject, which you would do well to read; and you will see in it that all sorts of birds, quadrupeds, and even fishes, have, in their fore feet, wings, and fore fins, elements resembling those of the human hand and arm. Often, in comparing only two animals, you might fail to trace the slightest resemblance; but when one or two or more of other kinds are placed between them, you find a sort of ladder which, in an evident manner, unites the lowest with the highest tribes.