6 
PREFACE. 
the top of the plates, corresponding with the folios, show the 
consecutive order in which they were published, and the 
figures at the bottom of the plates and folios have been added 
to assist in the systematic arrangement; but unfortunately 
they rarely occur at present, as it was impossible to insert 
them until the entire arrangements were concluded. The 
dates at the bottom of the plates will determine when they, 
as well as the corresponding folios, were published ; but it 
must be remembered that the articles were written one month, 
and frequently in the summer, two or three months in ad- 
vance ; this may exculpate me occasionally from an appear- 
ance of neglect, or possibly plagiarism, when similar subjects 
have been treated of, about the same periods by other writers. 
It is far from improbable that some of the dissections may 
not be free from error, for portions which are soft like the 
labium, will be frequently injured by the knife in the separa- 
tion of minute parts, and under high powers the slightest 
perspective or foreshortening materially alters the outline of 
an object, so that compressed joints may appear too narrow 
and others too short. From the great care that has been taken, 
it is presumed such are rare exceptions; but it is important to 
be borne in mind, in order that such anomalies may not affect 
any theory based on the constancy of figure ; for as far as my 
observations extend, there is no greater variation in the oral 
organs of individuals of the same species and sex, than there 
is in their antennae or tarsi. 
Notwithstanding all difficulties, and they have neither been 
few nor trifling, X have devoted myself most assiduously to 
my task during its progress, that no delay might take place 
in the accomplishment of an object which I considered would 
be for the benefit of science; and for sixteen years my Cabinets 
and Library have been open to my friends and scientific men 
one day in each week, in the hope that my favourite pursuit 
would be thereby advanced ; and if they have gained informa- 
tion or derived advantage from this arrangement, I am well 
satisfied. This, however, caused so great a diminution of my 
time, that it would have taken upwards of twenty years to 
complete this work, without allowing any periods for relax- 
ation, if I had not called in the aid of artists to assist me in 
the engravings : I wish it, however, to be understood that the 
plates of several of the early Volumes w^ere for the greater 
