Introduction 



of the United States National Museum. The text figures for the 

 most part are printed from electrotypes made from blocks which 

 are the property of the United States Department of Agriculture, 

 and many of them have illustrated previously published articles 

 by the writer. 



A word must be said in regard to the literature references 

 which follow the consideration of most of the groups. Nearly 

 all of the papers mentioned have been published either by Gov- 

 ernment institutions or by learned societies and scientific periodi- 

 cals. Very few of them have been published as separate books, 

 but such as have been published in this way, if of comparatively 

 recent date, may be obtained from book dealers. The periodicals 

 and transactions of scientific societies may be obtained through 

 the societies which publish them and through the publishers but 

 in the case of Transactions and Proceedings, single volumes, 

 and more especially single papers, are seldom sold, and the older 

 ones are liable to be out of print. Moreover, the expense of 

 purchasing all of the periodicals containing the publications on 

 the different groups of insects will be so great that few workers 

 can afford it. But there is a custom among writers on these 

 topics of securing a certain number of separate copies of their 

 papers, and these are freely distributed, so that it often happens 

 that a person interested can obtain a copy of a scientific paper by 

 writing to the author. The American Entomological Society, of 

 Philadelphia, has published a little directory containing the 

 names and addresses of those interested in the study of insect 

 life in the United States and Canada, and from this directory the 

 addresses of all living writers on insects in North America can 

 be obtained. Many of these "author's separates " can be pur- 

 chased from dealers in second-hand books, and the American 

 Entomological Society, of Philadelphia, and a few other societies 

 here and in Europe offer many of these author's extras for sale, 

 and in some cases publish lists. Moreover, there are certain 

 establishments through which the student can buy nearly all of 

 the works and separates which he needs. These are dealers in 

 natural history books and papers, and many of them publish 

 catalogues which are sent free on application. Bulletin 24, new 

 series of the Division of Entomology, United States Department 

 of Agriculture, contains a list of these dealers which publish 

 catalogues, and this bulletin is sent freely to all applicants. 



viii 



