PREFACE. 



The account which follows has been written by Mr. Stanley 

 Hirst, and it deals with species of Arachnids and Myriopods 

 which are in any way injurious to man. The Myriopods, 

 including the animals known as Centipedes and Millipedes, 

 are relatively unimportant in this respect. The greater part of 

 the description accordingly deals with the Arachnids, animals 

 which can usually, though not always, be distinguished from 

 insects by having four pairs of ordinary walking legs instead 

 of three pairs. This great division of the Arthropoda includes 

 the Itch-mites, which are true parasites ; the Scorpions, for- 

 midable by reason of the poisonous sting with which the hind 

 end of the bod}- is provided ; the Spiders, a few of which are 

 feared on account of their poisonous bite ; and the Ticks and 

 Harvest-bugs, one or two forms of which during the operation 

 of sucking the blood of a human victim may introduce into 

 his system the microscopic organisms which give rise to some 

 serious disease, while others cause great irritation by their bites. 



The animals here considered have thus a very practical 

 interest, which fully justifies their inclusion in an economic 

 series of publications. It is hoped that the present number 

 will be followed, in due course, by others dealing with Arachnids 

 which are injurious to domestic animals. 



Plates I. and II. and text-figures 8, 13, 14, and 15 are 

 reprinted from figures which have already been published else- 

 where. The thanks of the Trustees are due to Mr. Walter E. 

 Collinge, Dr. G. A. K. Marshall, and Dr. A. Castellani for 

 permission to make use of these figures. 



SIDNEY F. HAEMER, 



Keeper of Zoology. 



British Museum (Natural History), 

 Cromwell Eoad, London, S.W. 7. 



April 5th, 1917. 



