X INTRODUCTION 



entomologists' cyanide killing-bottles and no less than 1,547 speci- 

 mens were taken from a jar of casein that had been stoppered for 

 twelve years. The fly Psilopa petrolei inhabits puddles of crude 

 petroleum; and both flies and beetles abound in certain hot springs 

 in the western United States where the temperature approaches 

 50° C. The largest insects include the African Goliath beetle, 

 Goliathus regius which measures four inches in length and two in 

 breadth, and the Venezuelan Dynastes hercules, reaching a length 

 of 6\ inches, while the magnificent butterfly Ornithoptera victoriae 

 of the Solomon Islands has a wing-span exceeding one foot. In 

 contrast some of the parasitic Hymenoptera are considerably less 

 than one hundredth of an inch in length, despite the complexity of 

 their structure. 



The diversity and versatility of the insects is nowhere equalled 

 in the animal kingdom, but in this volume I hope to show that the 

 other terrestrial Arthropoda, although somewhat neglected, will 

 well repay further acquaintance. 



For many years, the majority of zoologists who have worked on 

 the Arthropoda have tended to concentrate their efforts either on 

 the marine Crustacea or on the insects. Apart from systematists, 

 comparatively few have paid more than superficial attention to the 

 remaining members of the phylum and although increasing num- 

 bers are now doing so, there is ample scope for new recruits as the 

 reader will soon realise. 



It is now generally recognised that the Collembola are not in- 

 sects and the same may be true of other Apterygota. Nevertheless, 

 these animals have always come within the scope of the entomolo- 

 gist and receive attention in many well-known entomological text- 

 books. I have not, therefore, included them in this book even 

 though the Pauropoda and Symphyla have been noticed. Indeed, 

 it is now believed that the latter are closely related to the Insecta. 

 Consequently the selection of groups discussed in the following 

 chapters may appear somewhat arbitrary from a systematic point 

 of view: but it will, I hope, be found to have practical justification. 



Life on land entails a number of problems for animals. Larger 

 forms require structural support, respiratory organs must become 

 modified for air breathing and there is no longer the surrounding 

 water into which toxic excretory products can freely diffuse, while 



