Introduction

Abstract

Insects are segmented animals with a relatively tough integimient and jointed limbs. They breathe by means of air-tubes or tracheae and the body is divided into head, thorax and abdomen. The head is the sensory and feeding centre, bearing the mouthparts and a single pair of antennae, perhaps homologous with the antennules of the Crustacea; compound eyes are usually present and often simple eyes or ocelli. The thorax is the locomotor centre, carrying three pairs of legs and usually two pairs of wings. The abdomen is the metabolic and reproductive centre; it contains the gonads and organs of digestion and excretion and usually bears special structures used in copulation and egg-laying. When it leaves the egg, the young insect differs more or less extensively from the adult form and its development therefore involves some degree of metamorphosis.