insects, as describing their habits and anatomy; but his six great volumes are still most valuable memorials of his conscientious care. He says that the number of observations necessary for a tolerably complete history of so many minute animals is prodigious. When one reflects on all that an accomplished botanist ought to know, it is enough to frighten him. His memory is loaded with the names of twelve or thirteen thousand plants, and he is expected to recall, on occasion, the image of any one of them. There is perhaps not one of those plants but has insects peculiar to itself; and some trees, such as the oak, give sustenance to several hundred different species. And after all, how many are there that do not live on plants? How many species that devour others? How many that live at the expense of other animals? How many species are there, some of which pass the greater part of their time in water, while others pass it entirely there? The immensity of nature’s works is nowhere more apparent than in the prodigious multitudes of these little animals. This being the case, he deems it impossible for any one man to acquire a knowledge of all the insects of even a limited district; therefore, instead of burthening the memory with the characteristic distinctions of these creatures, to the neglect of matters of greater importance, he recommends attention to particular _genera_, and especially to those which are of most frequent occurrence, that a knowledge of their peculiarities, food, and propagation, and the different forms they assume, may be accurately obtained. In the first two volumes, Réaumur treats of caterpillars, their changes of form into the chrysalis, and this into the butterfly; about their different kinds and habits, and concerning the other insects which attack them, and live within them, in their early stage. The third volume includes the description of the habits of the clothes moths, and the plant-lice, or aphides; the fourth treats of gall insects and two-winged flies; the fifth contains the history of bees, and the sixth of wasps and hornets. The natural history of the grasshoppers, crickets, and beetles was to have been written in a seventh volume, but it was never completed. The published volumes contain much very valuable information, and their great merit consists in the wonderful care Réaumur took, in investigating facts and in recording them carefully and systematically. He especially studied the instincts of insects, and thus brought their nervous system into prominent notice, and also the evident connection between the surrounding conditions and the peculiar lives of animals.