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Art. XLVII. — On the Comparative Structure of the Scutellum 

 and other Terminal Dorsal Parts of the Thorax of Winged 

 Insects. By J. O. Westwood, F.L.S., &c. 



LiNN/EUSj in his def]nition of insects, (Syst. Nat. I. ii. 533,) 

 thus describes the part of the body intermediate between the 

 head and abdomen: — "Truncus inter caput et abdomen 

 pedatus : thorace supra dorso, postice scutello, subtus pectore 

 sternoque." Thus the term thorax appears to have been used 

 as identical with truncus, and to comprise on its upper surface 

 the dorsum and scutellum, and on its inferior surface the pectus 

 and sternum ; but in his descriptions he applied the term 

 thorax either to the entire truncus, or to the prothoracic shield 

 alone, as in the beetles. Fabricius, in his *' Philosophia 

 Entomologica," defines the truncus as being " inter caput et 

 abdomen, constat thorace, scutello, pectore, sterno ;" and the 

 scutellum thus : — " Thoraci postice adhaerens inter alas por- 

 rectum, cohseret quidem cum thorace manifeste tamen distinc- 

 tum. Usus scutelli inter volandum alas expandere videtur." 

 Thus it is evident that Fabricius regarded the thorax (as we 

 now call his truncus) as divisible into a dorsal and ventral 

 portion; his thorax and pectus constituting the dorsal and 

 ventral anterior part, and his scutellum and sternum the dorsal 

 and ventral posterior part. The part which in the beetles 

 occupies the triangular space at the base of the elytra, was 

 considered by him as the scutellum. 



But a more philosophical mode of treating the thorax was 

 by degrees introduced by Knoch, lUiger, Latreille, and others : 

 it is, however, to Audouin that we owe the clearest elucidation 

 of its various complicated parts. Bringing to the subject a 

 most philosophical spirit, deeply imbued with the value of 

 comparative anatomy, he perceived that the mass of organiza- 

 tion to which the name of thorax had been applied, was, in fact, 

 formed of three distinct segments — prothorax, mesothorax, and 

 metathorax — soldered together, subject to the same general 

 principles which govern other segments, and differing only 

 from them in being the" seat of the organs of motion ; which, 

 from their various degrees of development, necessarily rendered 

 the extent of development of the different thoracic segments 

 themselves equally variable. On the upper surface of each of 



