PROCEEDINGS OF THE 



ENTOMOLOGICAL SOCIETY OF WASHINGTON 



VOL. 20 MARCH, 1918 No. 3 



THE THORACIC SCLERITES OF IMMATURE PTERYGOTAN IN- 

 SECTS, WITH NOTES ON THE RELATIONSHIPS INDICATED. 



BY G. C. CRAMPTON, PH.D. 1 



Numerous studies of the thoracic sclerites of adult insects in 

 recent years, have resulted in the homologizing of the plates in 

 most of the orders ; but the knowledge thus gained has never been 

 applied to immature Pterygotan insects in general, or to the 

 Apterygotan forms. In attempting to determine the homolo- 

 gios of the sclerites in immature insects, it has been found neces- 

 sary to make a study of the thoracic sclerites in Apterygotan in- 

 sects, in order to establish, as far as possible, the original condi- 

 tion of the parts in question. The detailed discussion of the 

 thoracic sclerites of the Apterygota, however, can be more profit- 

 ably taken up in a separate paper, and they have therefore been 

 only very briefly referred to in the following discussion. 



Since the hoinologies proposed in the present paper, were 

 largely determined by a comparison of the sclerites of immature 

 Pterygotan insects with those of the more primitive Apterygotan 

 forms, from an evolutionary point of view, it has been the source 

 of no small gratification that the conclusions arrived at from a 

 phylogenetic study of the parts, are in accord \vith the results 

 obtained by Dr. Boving and Mr. Craighead, who are investigat- 

 ing the question from an entirely different standpoint namely 

 from a study of the muscles attached to the parts in question. 

 The study of the musculature is of the utmost value in attempting 

 to establish any obscure homologies, since the muscles frequently 

 remain 'distinct and practically unchanged in character, after 

 the sclerites to which they are attached have become indistin- 

 guishably fused together, or have undergone some rather dis- 

 concerting re-combinations, or shifting of position, with reference 

 to the usu;il landmarks used in identifying them. I am therefore 

 greatly indebted to Dr. Bfiving and Air. Craighead for allowing 

 me to look over their drawings of a wide range of forms, and for 



1 Contribution from the Entomological Laboratory of the M:iss:i<-lm- 

 *<'tls Agricultural College, Ainhcrsl, .Mass. 



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