seem as appropriate now as the original balance was when Dr A. D. Imms'
textbook was first published over fifty years ago. There are 35 new
figures, all based on published illustrations, the sources of which are
acknowledged in the captions. We are grateful to the authors concerned
and also to Miss K. Priest of Messrs Chapman & Hall, who saved us from
many errors and omissions, and to Mrs R. G. Davies for substantial help
in preparing the bibliographies and checking references. London O.W.R.
May 1976 R.G.D. Part I ANATOMY AND PHYSIOLOGY Chapter I INTRODUCTION
Definition of the Insecta (Hexapoda) The insects are tracheate
arthropods in which the body is divided into head, thorax and abdomen. A
single pair of antennae (homologous with the anten- nules of the
Crustacea) is present and the head also bears a pair of mandibles and
two pairs of maxillae, the second pair fused medially to form the
labium. The thorax carries three pairs of legs and usually one or two
pairs of wings. The abdomen is devoid of ambulatory appendages, and the
genital opening is situated near the posterior end of the body.
Postembryonic development is rarely direct and a metamorphosis usually
occurs.