ADVERTISEMENT. 
THE publication of the concluding volumes of 
the “Introduction to Entomology” has been un- 
avoidably delayed by the continued ill health of 
one of the authors, which has devolved upon the 
other a considerable increase of labour, and de- 
manded a greater expenditure of time than would 
otherwise have been required: for though Mr. 
SPENCE put every facility in Mr. Krrpy’s power, 
and had drawn up arough copy of every Letter 
belonging to his department; yet, as most of 
them had been written several years ago, many 
curious facts, and a great variety of interesting 
information subsequently derived from various 
sources, were necessarily to be inserted, and the 
whole to be prepared for the press. 
When the thousands of objects that were to be 
examined, and many of them repeatedly, in com- 
posing the Letters on the External Anatomy of 
Insects, are considered, it will not appear sur- 
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