Entomology, and indeed natural history generally, uses three words, very much alike, but very different in signification and application. These are, _habit_, _habits_, and _habitat_. The habit is that peculiar character of identity, that _je ne sais quoi_, which marks all the species of a genus collectively, and which, in some cases, only the trained eye can detect. It is then seen instantaneously, and forcibly illustrates the extreme precision the study of the natural sciences tends to cultivate. Their utility, also, as a discipline to the mind, conjunctively with the keen accuracy which practice gives the sight, are qualifications not lightly to be esteemed. It is from such absolute control of detail that the most efficient power of generalizing emanates, which, when it has once become habitual, gives, from its rapidity, an almost instinctive facility, as its inevitable concomitant, for both synthetical and analytical survey. The mind thus becomes strengthened by vigorous exercise, and has always, for every purpose, a powerful instrument at command, often used unconsciously, but always effectively. Thus is _habit_, once correctly perceived, ever retained. The _habits_ are the peculiar manners and economy of a species; and the _habitat_ is the kind of locality the creatures affect, such as hill or plain, wood or meadow, forest or fell, hedgebank or decaying timber, sand or chalk or clay, and ground vertical or horizontal; and the _metropolis_ of a species—another term in use—is the centralization of the general habitat where the insect either nidificates collectively with its fellows, or, where, from any other cause, it may be found in its season, usually in profusion. But good fortune does not always attend the discovery of this locality. It is by the acquired skill of perceiving habit, that a large and confused collection may be sorted rapidly, or fresh captures immediately placed with their congeners, without the necessity of going tediously through all the descriptive characteristics. Incidental errors are afterwards speedily corrected. It is then that the specific character exhibits its utility by enabling us at once to distinguish the new from the old. The concentration and summary of the specific character is the name of the species, or trivial name as it is sometimes called, which is, as it were, the baptismal designation that attaches to it always afterwards, and is contemporaneous with the introduction of the creature into the series of recognized beings.