Preface 
occur in North America north of Mexico, the effort was made to 
select those species which would adequately represent the various 
families and the commoner and more important genera, thus pro¬ 
viding a work which might serve as an introduction to the study. 
This process of selection had to be made with much patience and 
care. Another cause of delay arose from the fact that it is some¬ 
times difficult to obtain perfect specimens for purposes of photo¬ 
graphic reproduction. Even where species are well known and 
common, and are abundantly represented in the collections to 
which I have access, it has not infrequently happened that it was 
almost impossible to discover specimens so perfect as to allow 
of their being reproduced by color-photography in a satisfactory 
manner. Minor defects, which signify little to a working natural¬ 
ist, and which can easily be eliminated from sight by a draughts¬ 
man, become very serious blemishes when resort is had to methods 
of photographic illustration. Much time had, therefore, to be spent 
in searching through various collections for the kind of material 
which was required, and often in remounting specimens which, 
while good enough for the cabinet, were not so set as to permit 
them to be employed in the photographic laboratory. Patience 
and perseverance, however, always bring in due time their re¬ 
ward, and I have been able to assemble enough properly prepared 
material to enable me in the main to accomplish my purpose. 
“Brevity is the soul of wit,” and this fact has not been 
forgotten by the writer in preparing the pages of this book. The 
limitations necessarily imposed by the space available precluded 
the preparation of lengthy descriptions. This brevity in descrip¬ 
tion is, however, as the writer believes, abundantly compensated 
for by the illustrations in the Plates. One good recognizable 
figure of a species is worth reams of mere verbal description. 
Those who desire to go deeply into the subject, and who wish 
to famiMarize themselves with all its technicalities, will find in 
the list of works named in that part of the introduction devoted 
to the bibliography of the subject much that they desire. 
I am indebted to many scientific friends for assistance, but to 
no one am I more indebted than to Dr. L, O. Howard, the Ento¬ 
mologist of the United States Department of Agriculture and the 
Honorary Curator of Entomology in the United States National 
Museum, and to his amiable associates, Dr. William H. Ashmead 
viii 
