Besides, there is another advantage of knowing the species of animals, and distinguishing them one from another, which is by regarding those as one and the same species, who, by means of copulation, produce and perpetuate beings like themselves; and as a different species, those from a connection between whom nothing is produced, or whose product are unlike their parents. Thus a fox will be a different species from a dog, if nothing results from a copulation of a male and female of these two animals, and when even there should result a bipartite animal, or a kind of mule, which cannot generate, that will be sufficient to establish the fox and dog of two different species. There is not the same advantage to be had in plants, for although some have pretended to discover sexes, and although divisions of breeds have been established by the parts of fecundation; yet, as these distinctions neither are so certain, nor so apparent as in animals, and the production of plants is made in many modes, that the sex has no part in, and where the parts of fecundation are not necessary, this idea cannot be made use of with any success; it is only on a misapprehended analogy that this sexual method has been pretended to distinguish all the different species of plants. Notwithstanding the number of animals is greater than that of plants, yet that is not the case with respect to the number of individuals in each species. In animals as well as in plants, the number of individuals is much greater in the small species than in the large. Flies are, perhaps, a million times more numerous than elephants; so likewise there are more kinds of plants than trees; but, if we compare the quantity of individuals in each species, we shall find that the plant is more abundant than the animal; for example, quadrupeds bring forth but a small number of young, and at considerable distances of time; trees, on the contrary, produce every year, a great quantity. It may be said that this comparison is not exact, and to render it so, we should compare the quantity of seeds produced by a tree, with a quantity of germs contained in the semen of an animal, and then, perhaps, we should find, that animals are still more abundant in their seed than vegetables. But it should be considered that it is possible by collecting and sowing all the seeds of an elm, for instance, that we might have 100,000 young ones from the product of a single year; and that should we supply a horse with as many mares as he could cover in one year, there would be a great difference between the production of the animal and that of the vegetable. I shall not examine into the quantity of germs; first, because we are not acquainted with it in the animal creation: and secondly, because possibly there is the same number of seminal shoots in the vegetable: for the seed of a vegetable is not a germ, being as perfect a production as the foetus of an animal, and to which, like that, a greater expansion is only wanting.