“About twelve hours later, after some little wriggling, the ventral triangle formed by the covering of the head, antennae and mouth parts falls open trap-door fashion, the antennae covers serving as hinges and the flexing point being about one-third of the distance up the wing covers from the abdomen. There is also a dorsal cleavage following the medial dorsum to the first abdominal segment, then the outline of the wing covers to a point half way to the end of the antenna covers. The crumpled-winged imago wriggles out and mounts the empty shell, to which it clings by the four hinder limbs, turning the entire body back and forth as if mounted on a pivot. In each of these turns the body describes an arc of nearly 90 degrees, the body being held stiff. The angle of the body is about 45 degrees from the vertical, the head being uppermost. The proboscis is usually partially unrolled. In five or six hours the soft, wrinkled wings spread and harden, and the insect is able to fly. A thin, transparent liquid, and sometimes a thick, reddish substance, are voided by the newly emerged butterfly.” CHAPTER V THE CLASSIFICATION OF BUTTERFLIES In every science it is necessary to manipulate a large number of related facts, and this cannot be done unless the data are arranged in some systematic and orderly fashion. In order to make use of the facts about butterflies, one must know something of the relation of one butterfly to another, and the relation of butterflies in general to the rest of the animal kingdom. SUBKINGDOMS, CLASSES, ORDERS, AND SUBORDERS Members of the animal kingdom which have no spinal column, but only an external skeleton composed of horny rings, are assigned to the subkingdom _Arthropoda_. Arthropods which have six legs are grouped together in the class _Insecta_. Insects with scales on their wings are assigned to the order called _Lepidoptera_. This order is divided into two suborders, the _Rhopalocera_ or butterflies and the _Heterocera_ or moths. Butterflies fly in the daytime, and have slender antennae with club-like knobs at the ends; moths are usually nocturnal or crepuscular, and their antennae are not knobbed, but are thread-like, feather-like, or hooked at the extremity. THE FOUR FAMILIES The suborder Rhopalocera is divided into four families: the _Nymphalidae_, the _Lycaenidae_, the _Papilionidae_, and the _Hesperiidae_. The _Nymphalidae_ or four-footed butterflies make up the largest family; the first pair of legs are much smaller than the others, and are quite useless for walking. Most of the Nymphalidae are large or medium-sized butterflies. The caterpillars are usually provided with spines or fleshy protuberances, and the chrysalids are always suspended by the tail.