44 PROCEEDINGS OF THE ACADEMY OF [Jan., 



only serve as firmer supports than the softer yielding integument about 

 them, but would likewise serve as protective plates. Contact with 

 external objects and mechanical irritation, such, for example, as the 

 rubbing of one part upon another, doubtless play no inconsiderable role 

 in the production of the sclerites. This was well illustrated in the case 

 of a young cricket, whose developing wing pads, by rubbing on the 

 tergum upon which they rested, left their outlines distinctly imprinted 

 in its integument. 



In addition to the formation of chitinous areas in the integument, 

 by the stimulus of its tension, muscular stress may likewise bring about 

 the breaking up of the large chitinous plates, or cause their division 

 into smaller regions by producing the infolding of hollow ridges, as is 

 shown in the tergum 13 and pleura. Again, it is quite evident that 

 portions of chitinous regions may become detached by muscular ten- 

 sion and drawn into another region, as is shown in the case of the 

 "migration" of the meron; such instances, however, are very rare, 

 and this method would consequently play an unimportant role in 

 sclerite formation. 



However, the method of sclerite formation, the theories of segmental 

 duplication, etc., are questions of minor interest, as the purpose of 

 this paper is to deal with the comparison of the sclerites in the adult 

 insect. With regard to the homologizations and terminology at present 

 in vogue, it may readily be seen that entomologists are by no means 

 agreed in these matters. Furthermore, the views here set forth fre- 

 quently differ very radically from those of other investigators, and on 

 this account the following list, which to some extent anticipates certain 

 points which will be brought out in a subsequent publication, may be 

 of some service, not only to furnish a resume of the synonyms, etc., 

 applied to the various sclerites, but also to give a brief outline of the 

 results here reached : — 



The Thorax. 



Thorax— Thorax (Nitzsch, '18). 



It is composed of the pro-, meso- and meta-thorax. 



The "thorax" of Strauss-Diirkheim, '28, is the meso- plus the meta-thorax. 

 Kirby, '28, following Fabricius, Linne and the other earlier writers, restricts 

 the term thorax to the notum or tergum, but these obsolete usages need 

 not be further discussed here. 

 Prothorax (') u — Prothorax (Audouin, '20). 

 = Protothorax (Nitzsch, '18). 



13 It is quite uncertain whether the postscutellum was separated from the 

 remainder of the tergum by muscular tension, or whether the postscutellum 

 was originally itself a distinct sclerite. 



14 The signs given in parentheses refer to the method of indicating the region 

 in question in the different figures. 



