"So were it not for the immense consumption as food which is made in nature of animals which compose the lower orders of the animal kingdom, these animals would soon overpower and perhaps destroy, by their enormous numbers, the more highly organized and perfect animals which compose the first classes and the first orders of this kingdom, so great is the difference in the means and facility of multiplying between the two. "But nature has anticipated the dangerous effects of this vast power of reproduction and multiplication. She has prevented it on the one hand by considerably limiting the duration of life of these beings so simply organized which compose the lower classes, and especially the lowest orders of the animal kingdom. On the other hand, both by making these animals the prey of each other, thus incessantly reducing their numbers, and also by determining through the diversity of climates the localities where they could exist, and by the variety of seasons--_i.e._, by the influences of different atmospheric conditions--the time during which they could maintain their existence. "By means of these wise precautions of nature everything is well balanced and in order. Individuals multiply, propagate, and die in different ways. No species predominates up to the point of effecting the extinction of another, except, perhaps, in the highest classes, where the multiplication of the individuals is slow and difficult; and as the result of this state of things we conceive that in general species are preserved" (p. 22). Here we have in anticipation the doctrine of Malthus, which, as will be remembered, so much impressed Charles Darwin, and led him in part to work out his principle of natural selection. The author then taking up other subjects, first asserts that among the changes that animals and plants unceasingly bring about by their production and _débris_, it is not the largest and most perfect animals which have caused the most considerable changes, but rather the coral polyps, etc.[165] He then, after dilating on the value of the study of the invertebrate animals, proceeds to define them, and closes his lecture by describing the seven classes into which he divides this group. II. _Recherches sur l'Organisation des Corps vivans, 1802 (Opening Discourse)._ The following is an abstract with translations of the most important passages relating to evolution: That the portion of the animal kingdom treated in these lectures comprises more species than all the other groups taken together is, however, the least of those considerations which should interest my hearers. "It is the group containing the most curious forms, the richest in marvels of every kind, the most astonishing, especially from the singular facts of organization that they present, though it is that hitherto the least considered under these grand points of view.