It must be owned, that in insects, fish, and shell-fish, there are species which seem to be very abundant; oysters, herrings, fleas, beetles, &c. are perhaps in as great numbers as mosses and the most common plants; but on the whole, the greatest number of the animal species is less abundant than the vegetable; and by comparing different kinds of plants with each other, there is not found such great differences in the number, as in the animal species; some of which bring forth a prodigious number, and others only a few; whereas the number of productions in plants is always very great throughout.
By what we have observed, it appears that the smallest and basest species seem to be the most prolific: the most minute are the most plentiful as well in animals as in plants, and in proportion as the animals are more perfect, they appear to decrease in number of individuals. Can it be thought, that certain forms of the body, as those of quadrupeds and birds, requisite for the perfection of sensation, would cost nature more organic particles than the production of less important animals?
Let us now pass to the comparison of animals and vegetables, with respect to situation, form, and size. The earth is the only place wherein vegetables can subsist. The greatest number grow above the surface, and are attached to the soil by roots. Some, as truffles, are entirely covered with earth, and a few grow under the water, but all require the surface of the earth to exist upon. Animals, on the contrary, are more generally dispersed; some dwell on the surface, and others in the bowels of the earth; some live at the bottom, and others swim in the waters of the ocean: some exist in the air, others dwell in the internal parts of plants, on the bodies of men and other animals, liquors, and even stones are not without them.
By the use of the microscope, a great number of new species of animals have been discovered: but singular as it may appear, we have not found more than one or two new species of plants by the help of this instrument. The small moss is, perhaps, the only microscopical plant spoken of; and we might, therefore, imagine that nature refused to produce very small plants, while she formed animalcules with profusion; but we might deceive ourselves by adopting this opinion without examination, and our error might arise from plants, in fact, resembling each other more than animals; so that this moldiness, which we only take for a very minute moss, may possibly be a kind of forest or garden, filled with abundance of various plants, although we are unable to mark the difference.
By comparing the size of animals and plants there will be found a great inequality, for the distance is much greater between the size of a whale and one of these microscope animals, than between the highest oak and the moss we are now speaking of. Although bulk be only a relative attribute, it may, nevertheless, be useful to inspect into the extreme boundaries nature has allotted to her productions. In bigness animals and plants seem to have a near equality; a large whale and a large tree forms a volume not very different; whereas, among the small it has been asserted there are animals so very minute that a million of them united together, would not equal, in size, the smallest moss-plant ever seen.
The most general and most sensible difference between animals and vegetables is that of figure, for the form of animals, although infinitely varied, has not any resemblance to that of plants; and although the polypus will, like plants, reproduce by cutting, and may be regarded as the link between the animal and vegetable kingdoms, not only by the mode of their reproduction but also by their external form, nevertheless the figure of the animal is so different from the external form of a plant that it is difficult to be deceived therein. Some animals form things resembling plants or flowers, but plants never produce any thing like an animal; and those admirable insects which produce and form the coral, would not have been taken for flowers if coral had not been regarded as a plant. Thus the errors wherein we might fall, by comparing plants with animals, will never have any influence but on a few objects which compose the link between both, and the more observations we shall make the more we shall be convinced that the Creator has not placed a fixed line between animals and vegetables; that these two species of organized beings have many more common properties than real differences; that the production of an animal does not require of nature more, and possibly, less exertion than that of a vegetable; that in general the production of organized beings does not require exertion, and that, in short, the living animated nature, instead of composing a metaphysical degree of beings, is a physical property, common to all matter.
OR [BH]REPRODUCTION IN GENERAL.