538 EXTERNAL ANATOMY OF INSECTS. 



the prothorax is producted posteriorly into a long scu- 

 telliform horizontal horn, which more or less covers the 

 wings and abdomen ; a circumstance which also distin- 

 guishes the genus Acrydium F. (Tetrix Latr.). This 

 horn seems to have been sometimes regarded by Linne 

 and Fabricius as a real scutellum, and sometimes only as 

 a process of the prothorax : but that it is merely the 

 latter will be evident to you, if you examine carefully 

 any insect furnished with this appendage ; for if you re- 

 move that part, you will discover the true scutellum and 

 other parts of the trunk concealed beneath it. A very re- 

 markable prothoracic appendage is exhibited by some 

 species of Mantis. In general the part we are treating 

 of in this tribe is very slender ; but in M. strumaria, gon- 

 gyloides, &c, it appears dilated to a vast width, and as- 

 sumes, either partially or generally, a subrhomboidal 

 form ; but if it is more closely examined, it will be found 

 that the form of the prothorax is really similar to that of 

 the rest of the tribe, but that this part is furnished on 

 each side, either on its whole length or anteriorly, with a 

 large membranous flat subtriangular appendage resem- 

 bling parchment 5 . Perhaps this kind of sail may be useful 

 to the animal in flight. In Prionus coriarhis &c. its sides 

 are armed with teeth, and in many Lamia, Cera?nbyces, and 

 other Capricorn beetles, and often in various bugs (Pen- 

 tatoma Latr.) with sharp fixed spines. But the protho- 

 rax has moveable as well as fixed appendages ; of this 

 kind are those spines (umbones), whose base is a spheri- 

 cal boss moving in an acetabidum of the thoracic shield 

 of the Capricorn subgenus Macropus Thunb. If I might 



* Stoll Spectres t. si./. 43. t. xii./. 45. t. xvi./. 58, 59. 



