IV PREFACE. 



take each his particular species, and give us a distinct 

 account of the frame and the texture of its parts, and 

 particularly those which distinguish it from other 

 animals. This would he one of the best services that 

 they could do to mankind," &c. Bacon thought that 

 it was within the capacity of man to control, and even 

 to command, the forces of nature. But our steps in 

 the investigation of biological problems must for a long 

 time be faltering. Even the first great generalizations 

 of Newton and of Darwin will require modification, as 

 our knowledge becomes more exact, and our materials 

 for reasoning, based on experiment, accumulate. In 

 such a manner, safe induction passes into practical 

 deduction, and experiment becomes the best proof of 

 acquired knowledge. 



The present treatise is offered to a discerning and 

 not unkind public, with the hope that it may lessen 

 the labour of the student by gathering together the re- 

 searches of others into small compass. Here and there 

 some new items have been added by the author towards 

 the history of this interesting group of insects. 



The comparison of specimen with specimen forms 

 the basis of all zoological and biological research. 

 Doubtless, after a comparison with identified living 

 forms, collation with museum specimens is of the 

 greatest value to the investigator. Specimens are 

 not, however, open to the use of all. To those 

 who have no access to them, figured monographs 

 are of prime importance ; but in consulting them, 

 it must be remembered that the colouring of livmg 

 specimens is often more marked than those of museum 

 examples, which commonly lose their brilliance and 

 freshness, however carefully preserved. 



