VI PREFACE. 



very grateful to M. TuUberg, who has been so good as 

 to send me several Swedish species, and has thus enabled 

 me to form in these cases a more decided opinion than 

 could otherwise have been possible. I must also 

 express my thanks to Mr. Mclntire for much assist- 

 ance in the collection of English species, as well as for 

 many valuable suggestions. 



The scales of the Thysanura and Collembola have 

 long been a subject of much interest to microscopists. 

 Through the kindness of Mr. J. Beck I am able to 

 give some beautiful plates of scales drawn by his 

 brother, the late Mr. R. Beck. Mr. J. Beck has added 

 a detailed description of these plates, as well as some 

 interesting remarks on the subject, which \\dll be found 

 in an Appendix. I regret that I did not receive these 

 descriptions in time to introduce them under the heads 

 of the several species. 



In the present work I have confined myself to the 



existing species, as I have not had the opportunity of 



studying any extinct representatives either of the 



Collembola or Thysanura. If, however, the views 



advocated in the third chapter are correct, both types 



must have had their origin far back in geological time. 



From the fragility of their structure we can hardly 



hope that the extinct forms will ever be well known 



to us. Yet the prospect is not so hopeless as it might 



at first sight appear. A certain number of fossil 



species have already been discovered. Koch and 



Berendt, for instance, in their work " Die in Bernstein 



befindlichen Cms. Myr. Arach. und Apteren der 



Vorwelt," published at Berlin in the year 1854, 



describe species of Smynthnrns, Isotoma, Jjogeeria, 



LejmDia, and Marhilis, and also a form, characterised 



