Destruction and reproduction, the great laws of nature, are carried on very greatly through the instrumentality of insects; and the same principle regulates even the increase of particular species of insects themselves. When aphides are so abundant that we know not how to escape their ravages, flocks of lady-birds instantly cover our fields and gardens to destroy them. Such considerations as these are thrown out to show that the subject of insects has a great philosophical importance--and what portion of the works of nature has not? The habits of all God's creatures, whether they are noxious, or harmless, or beneficial, are worthy objects of our study. If they affect ourselves, in our health or our possessions, whether for good or for evil, an additional impulse is naturally given to our desire to attain a knowledge of their properties. Such studies form one of the most interesting occupations which can engage a rational and inquisitive mind; and, perhaps, none of the employments of human life are more dignified than the investigation and survey of the workings and the ways of nature in the minutest of her productions. The exercise of that habit of observation which can alone make a naturalist--"an out-of-door naturalist," as Daines Barrington calls himself--is well calculated to strengthen even the most practical and merely useful powers of the mind. One of the most valuable mental acquirements is the power of discriminating among things which differ in many minute points, but whose general similarity of appearance usually deceives the common observer into a belief of their identity. The study of insects, in this point of view, is most peculiarly adapted for youth. According to our experience, it is exceedingly difficult for persons arrived at manhood to acquire this power of discrimination; but, in early life, a little care on the part of the parent or teacher will render it comparatively easy. In this study the knowledge of things should go along with that of words. "If names perish," says Linnæus, "the knowledge of things perishes also:"[J] and, without names, how can any one communicate to another the knowledge he has acquired relative to any particular fact, either of physiology, habit, utility, or locality? On the other hand, mere catalogue learning is as much to be rejected as the loose generalizations of the despisers of classification and nomenclature. To name a plant, or an insect, or a bird, or a quadruped rightly, is one step towards an accurate knowledge of it; but it is not the knowledge itself. It is the means, and not the end in natural history, as in every other science.