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.