This little book is the outcome of many years study of its subject prosecuted chiefly in the Natural History Museum, South Kensington. It owes much to the suggestions and criticisms of various friends and colleagues. Amongst these I would especially mention SIR GUY MARSHALL, F.R.S., late Director of the Commonwealth Institute of Entomology, MR R. I. POCOCK, F.R.S., late Superintendent of the Zoological Gardens, London, DR A. T. HOPWOOD, DR K. G. BLAIR, DR F. ZEUNER, DR F. VAN EMDEN, colleagues in the Natural History Museum, all if whom have been most helpful.
As to the photographic illustrations, it should perhaps be mentioned that none are taken from living specimens. Although some are represented in lifelike attitudes, these have been selected only to show their form to the best advantage and should not be regarded as affording evidence of their conditions of life.