INTRODUCTION. 
————— 
To know how to do a thing is a great step towards its ac- 
complishment; but to know exactly when to do it, is often 
the one thing needful to insure success, This applies with 
great force to the pursuit of Natural History, and particwarly 
to Lepidoptera. The regularity with which, at certain definite 
dates, most species of Butterflies and Moths ordinarily appear, 
is something almost marvellous; and many species are not 
obtained in fine condition through inattention to the time of 
their advent, while some may be missed altogether. The 
annual loss to Science in specimens and knowledge from 
Collectors not looking after Larve at the only times when 
they are to be found cannot be estimated, but it must be 
very great, } 
The want of a work giving in a concise form the necessary 
information where, and how to find Lepidopterous Insects each 
month, has long been felt, and particularly so of late years, 
when the attractions of the study of the Lepidoptera have 
hecome so largely recognized. But although there were many 
far more able Entomologists than the Author, who might 
have prepared such a work, nothing was done; and he has, 
therefore, made the attempt. In this, he has received the 
invaluable assistance of several of our ablest Entomologists, 
including My. F. Bond, Mr. P. H. Vaughan, Mr. J. W. Douglas, 
Rey. Joseph Greene, Rev. H. Harpur Crewe, Mr. Reading, 
Mr. Tearle, and others, to whom he desires to express his 
grateful thanks. 
