ARTICLE II. 
AN ESSAY ON THE DEVELOPMENT OF THE MOUTH PARTS OF 
CERTAIN INSECTS. 
BY JOHN B. SMITH, Sc.D. 
\ 
Read before the American Philosophical Society, February 21, 1896. 
Since the publication of my paper on the mouth parts of the Dzptera, printed in 
the Transactions of the American Entomological Society for 1894, I have continued 
gathering material, have examined the oral parts of a very large number of species of 
all orders, and am more than ever convinced that in all essentials the conclusions 
already published by me are correct —revolutionary as they seem at first sight. That 
my ideas have not found unquestioned acceptance is not surprising; but no one has, 
to my knowledge, published anything that disproves the points made by me. It has 
been suggested, however, because I have not made continual reference to the works of 
previous authors, that I was ignorant of the literature, and several papers have been 
cited as contradicting my conclusions. 
As a matter of fact I believe I am fully aware of all that has been written on the 
subject, and have, in each case where my attention has been called to a paper, studied 
it carefully, and found nearly always that the facts given bear me out, though the con- 
clusions are adverse ; simply because no author has seriously questioned the univer- 
sally accepted homology of the month parts in the various orders. My own studies 
have been made on a basis so radically different from any heretofore accepted, that my 
results must stand on them alone, and my conclusions, if valid, must stand on the facts 
as they appear to me. I have used principally the dissecting needles in my work; but 
have not neglected the section cutter. This latter instrument has been rather too 
much used at the expense of the needles, and its results, though undoubtedly accurate 
~as a record of facts, are easily misinterpreted if the basic homology which is assumed 
