The systematic arrangement of this tribe of insects has always been considered a task of great difficulty. So convinced of this was Latreille, who had himself studied the subject profoundly, that he says a classification of lepidoptera may be considered the touchstone of entomologists. This difficulty arises chiefly from the uniformity of organization which prevails throughout the order--a uniformity occasioned by all of them being designed to subsist on liquid food, and to imbibe it in the same manner. The oral organs, therefore, which are of the first importance in classifying other tribes--the coleoptera, for example, in which they undergo almost endless variations of form and consistency to fit them for consuming every kind of organic substance, from semi-fluid animal or vegetable matter to the hardest ligneous tissue--are, in this instance, of comparatively little avail. Recourse must be had to secondary and subordinate characters; and even when we are convinced that, owing to a peculiar _facies_, and the concurrence of many minute resemblances, certain groups should be regarded as distinct, it is found difficult to define them in a satisfactory manner. Neither has the difficulty been much lessened by the manner in which the subject has been handled by many modern naturalists. The numerous illustrations of lepidoptera published of late years, have been _partial_, being either selections from the whole class, or forming part of a local fauna. In either case, the subject is regarded in too insulated a light. The illustrator of foreign butterflies selects a species, and by giving prominence to all its minute characters, proposes it with considerable plausibility as a distinct genus. The local faunist divides his groups in reference to his own limited sphere of observation. Neither contemplates the possibility of being ever called upon to elaborate a general system, and he leaves it to those who are to reconcile all existing inconsistences. Hence it follows, that so many of the genera proposed in local and partial works can find no place in a general one; for however specious they may appear when standing alone, it is often found that they will not unite into a consistent whole, and they may therefore be said still further to embroil the very subject they were designed to elucidate.