As will be adverted to in the descriptive section, the English names of our butterflies have not always been quite the same as those now in general use. There has, however, been far less stability in scientific nomenclature, and very many changes in both generic and specific names have been made during the past twenty years, more especially perhaps within the last decade. Genera are now founded by some specialists on characters which formerly served to distinguish one species from another, whilst other authorities merge several genera in one upon certain details of structure that are common to them all. Patient research into the entomological antiquities has revealed much important material, some of which may furnish a new interpretation of the Linnean classification of Lepidoptera. The discovery of the earliest Latin specific name bestowed upon an insect, is a labour which entails a large expenditure of time and requires fine judgment. Great credit is therefore due to those who undertake such investigations, the result of which may tend to the establishment of a fixed nomenclature in the, probably not remote, future, although it sadly hampers and perplexes students in the meanwhile. All things considered then, it has been deemed advisable not to make many changes in specific names, and to retain the old genera as far as possible. The arrangement of families, genera, etc., will be found to accord with that most generally accepted both in England and on the continent. THE BUTTERFLIES OF THE BRITISH ISLES. PART I. THE LIFE CYCLE OF A BUTTERFLY. As is the case with all other Lepidoptera, butterflies pass through three very distinct stages before they attain the perfect form. These stages are:--1. The egg (_ovum_, plural _ova_). 2. The caterpillar (_larva_, _larvæ_). 3. The chrysalis (_pupa_, _pupæ_). The perfect insect is called the _imago_ (plural _imagines_). The Egg. Butterfly eggs are of various forms, and whilst in some kinds the egg-shell (_chorion_) is elaborately ribbed or fluted, others are simply pitted or covered with a kind of network or reticulation; others, again, are almost or quite smooth. If the top of an egg, such as that of the Purple Emperor (Plate 28), is examined under a good lens a depression will be noted, and in this will be seen a neat and starlike kind of ornamentation. In the middle of this "rosette" are, present in all eggs, minute apertures known as micropyles (little doors), and it is through these that the spermatozoa of the male finds entry to the interior of the egg and fertilization is effected. The changes that occur in the egg after it is laid are of a very complex nature, and readers who may desire information on this subject are referred to Sharp's "Insects," Part I., in the "Cambridge Natural History," where also will be found much interesting and instructive matter connected with the caterpillar and chrysalis, to which stages only brief reference can here be made. The Caterpillar.