400 EXTERNAL ANATOMY OF INSECTS. 



Although every insect is composed of thirteen segments, all 

 of these are not constantly observable ; the existence of all, 

 however, may be generally ascertained, though some of them 

 under great variation in appearance ; a segment occasionally 

 almost disappearing, and on the contrary sometimes nearly 

 hiding all the others by its magnitude;^ being occasionally 

 closely united to an adjoining segment •/ and again, sometimes 

 bearing on its surface an indentation ^ or fold,'' giving to it the 

 appearance of two : a segment, moreover, will frequently give 

 rise to processes ; these are of two kinds, — apophyses, which 

 are merely bony excrescences, and evidently an intrinsic part 

 of the segments ;' and epiphyses, which are distinct appendages, 

 with a moveable articulation -^ great care is therefore required 

 to avoid mistaking a mere process for a segment, and also to 

 insure against overlooking segments which really exist. 



For the thirteen segments observable in true insects, I 

 would propose the following names : ' 



No. 1. (A. B.) Caput, bearing the organs manducation, vision, &c. 



2. (C. D.) Prothorax, bearing the Propedes, or /ore-/e_(7S. (a) 



3. (E. F.) M.^soTnoB.xx,heoxmgi\\e V Ko A-LM, or fore-wings {e\ 



and the Mesopedes, or middle legs, (i) 



4. (G. //.) METATHORAX,bearingtheMETAL^,or/?.mi-wm^s(o), 



and Metapedes, or hind-legs, (u) 



5. (I. /.) Propodeon. 



6. (K. Z.) PODEON. 



7. (M. iV.) Metapodeon. 



8. (O. P.) OCTOON. 



9. (Q. R.) Ennaton. 



10. (S. T.) Decaton. 



11. (U. V.) Protelum. 



« The protliorax, for instance, is scarcely discernible in Musca, while Centrotus 

 appears ail prothorax. 



f As the metathorax and propodeon in Melolontha. 



8 As in Pulex. •> As in some Locusta. 



• As in the prothorax of Dynastes, Typheeus, &c. ; yet these apophysal appen- 

 dages appear to have been not unfrequently described, named, and figured as 

 primary parts ; thus introducing into our nomenclature a mass of parts, the com- 

 mon existence of which it were vain to attempt to trace. 



^ As the appendages to the telum in Phasma, Libellula, &c. 



' See Plate III. The letters between parentheses in this table apply to all the 

 figures in this and succeeding plates on this subject. 



