The importance and utility of these researches are unquestionable, and yet there is even more of novelty and interest in those which he made in natural history. For instance, he explained the means by which many shells, sea-stars, and other mollusca or zoophytes, execute their progressive motion. He likewise illustrated the curious manner in which the claws of crabs and lobsters are reproduced. He also threw a new light on the singular action of the torpedo, and the organ by means of which it is exercised, although the phenomena of electricity were not then sufficiently understood to enable him to perceive all the relations of his subject. In 1718, he published a memoir on the rivers of France, which contain grains of gold in their sands, and soon after described the immense beds of fossil shells known in Touraine under the name of _falun_. In 1723, he made observations on the lustre emitted by several kinds of shell-fish, especially the pholades, which perforate wood and stones. Physiology is indebted to him for the ingenious and decisive experiments which, in 1752, made known the difference that exists, with respect to digestion, between birds of prey, whose stomach acts on their food only by means of a solvent fluid, and granivorous birds, in which a very powerful muscular gizzard exercises a pressure sufficient to break down the hardest bodies and reduce them to powder. These labours might well have sufficed for a single life; but the most remarkable undertaking of Reaumur has not yet been mentioned. It is entitled Memoires pour servir a l'Histoire des Insectes, and extends to six quarto volumes, which were published between 1734 and 1742. This work occupied many years, and was the result of numerous observations made principally in his own garden, where he kept insects of all kinds, for the purpose of examining their habits, changes, and generation. It is, however, incomplete,--the locusts and grashoppers, as well as the whole tribe of coleoptera, having been intended for subsequent volumes, which never appeared.