M. 
PREFACE. 
has been done by such men as Siebold, Leydig, 
Schonfeld, Schiemenz, and others, to clear up difficult 
problems ; but unfortunately the results of their works 
are not always accessible, as they are scattered through- 
out the proceedings of different Societies. They have 
never yet been collected into one volume. Frequently 
these works have appeared as monographs treating of 
some particular organ, and valuable as these are to 
the general entomologist, they contain an immense 
amount of matter of little use to the specialist. The 
exhaustive manner in which the subjects are generally 
treated makes them very expensive and out of reach of 
the average student. When an attempt at compilation 
is made, frequently discoveries are mentioned without 
alluding to the names of the discoverers, and the 
student is at a loss to know to whom the discoveries 
are due, they being often erroneously attributed to 
the writers of these compilations. Many such books 
contain a large amount of superfluous matter, tending 
to increase the size and cost without adding to the 
value, and frequently theories long since abandoned 
are discussed merely for the purpose of refuting them, 
thus swelling the size of the volume. 
Having been engaged for many years in micro- 
