Page:Popular Science Monthly Volume 45.djvu/540

522 really only the grouping made in our mind of all the living individuals exhibiting the same form, and which we believe to be all united under a common parentage.

Yet form can not serve of itself to characterize life, for there exist other bodies than crystals in the inorganic world which are individuals. The planets and the rings of Saturn will at once occur as examples. We might also range in the same category comets and whirls of smoke, which are likewise individuals, and cease to be by the mere fact of their division or dissociation.

Form is therefore not sufficient to characterize the living individual. Let us see if the general features and external aspect of organized beings will not offer us marks to distinguish them from mineral bodies. The plane faces, the sharp edges, and the definite angles of crystals, and the spherical contours of the heavenly bodies, have been contrasted with the undulating surfaces, the less geometrical and more softly defined profiles of plants and animals. This trait is certainly not destitute of value, and the untrained mind is rarely deceived by it. Sometimes the lapidary, in cutting agate, uncovers delicate arborescent shapes in the transparency of the gem. The illusion is vivid, and one might fancy he had a petrified moss under his eyes. A lens will assure him that there is no vegetable fossil here, and will reveal an assemblage of crystalline needles that have nothing in common with the delicate articulations and waving lines of a genuine moss.

Its particular stamp is so clearly impressed on each living being and on each of its parts, and it is so recognizable that it guides the naturalist with certainty, even when he affirms, from the smallest remnant or weakest impression, the existence on the surface of the globe, in prodigiously distant times, of beings that lived then, and with which he is unacquainted. Some of the organisms have left only traces, and he affirms that life passed there, without knowing whether it was vegetable or animal.

The ancients, although they had not our experience in interpreting the true nature of fossils, never failed to recognize the factory mark which Nature impresses on its works. Science then gave no means of discerning in ammonites the shell of an animal allied to the squids and cuttlefish; but the finders had at least the feeling that these things had lived, and, by analogy, they saw in them the bones of animals preserved in the earth.

Form is not an essential attribute of life. There exist living beings destitute of living form, as there exist chemical substances that do not crystallize. The microscope reveals in stagnant water gelatinous masses that change their form and move incessantly. We see a part of the mass stretch out like a foot advancing. Then the whole being seems to pass into this prolongation, which is proportionately swelled out. Another expansion occurs at