lAr 





2 fii c £y 



CCCLILLETT LtLRAf.Y 

 Dr. E.G. Mitchell tonos,. ii_i 



AN ESSAY ON THE DKVP:L0PMP:NT OF THE MOUTBL PARTS OF 



CERTAIN INSECTS. 



liV JOHN i;. SJIITIl, Sr.l), 



Read before the American Philosophical Society, Febiuary 21, 1896. 



vSiuce the publication of my iiapci' on (lie moiitli parts of the Dipli-ra, jirintL'tl in 

 the Transaction^ of the American Eiitoinoloi;ieal Society for 189,4', I have continued 

 gathering material, have examined the oral parts of a very large number of species ol" 

 all orders, and am more than ever convinced thai in all essentials the conclusions 

 already published by me are correct — revoliitioiiarv as they seem a( (irst sight. That 

 my ideas have not found unquestioned acceptance is not siir[)i'ising ; but no one has, 

 to my knowledge, published anything that disproves the i)oints 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 sevi-ra! papers have been 

 cited as contradicting m\' conclusions. 



As a mattei- of fact I believe 1 am fully aware of all that has Itecii written on the 

 subject, and liavt', in each case whei'e my attention has been called to a ])aper, studied 

 it carefully, and found nearly always (hat the facts given beai- me out, though the con- 

 clusions are adverse ; sim|)ly because no author has seriously questioned the univer- 

 sally accejiteil homology of the month parts in the various ordei's. ls\\ own studies 

 have been made on a basis so radically dillerent 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 woi-k ; but 

 have not neglected the section cutter. This latter insti-ument has been rather too 

 much used at the e.x])ense of the needles, and its results, though uiidoulitedly accui-ate 

 as a record of facts, are easily misinterpreted if the basic homology which is assunuil 



