EXTERNAL ANATOMY OF INSECTS; 381 



a Commissura (the Commissura). A joint in the costal 

 nervure of the wings of Coleoptera, where they bend 

 to take a transverse fold a . 



b Tendo (the Tendon). A strong bristle, or bristles 

 observable at the base underneath in the under- 

 wings of many Lepidoptera, which plays in the Ha- 

 mus of the upper-wings b . 



c Hamuli (the Hooklets). Very minute hooks in the 

 middle of the anterior margin, observable in some 

 Hymenoptera, by which the under-wing is fixed to 

 the upper, to cause both to act as one organ in 

 flight c . 



d Pterygium (the Pterygium). In under-wings this is 

 a small wing-like appendage, fixed at the base of 

 the wing in some Lepidoptera d . 



e Alula (the Winglet). A small concavo-convex sca- 

 rious appendage, fixed behind the wings at their 

 base, in many Diptera e . 



f Halteres (the Poisers). Small capitate processes or 

 organs, observable under the wings of Diptera^ at- 

 tended by a spiracle f . 



B Metapnystega (the Metapnystega). A corneous 

 scale or lamina that covers the pneumatic organs 

 in the Mctatlwrax, situated sometimes in the Plea- 

 rce, as in the Coleoptera ; at others in the Postfrce- 

 num, as in Tenthredo L. ; and sometimes, as in the 

 Libellulina, between that part and the abdomen e . 



a Plate X. Fig. 4. d" . b Linn. Trans, i. t. xin.f. 1. b. 3. a. 



c Kirby Mon. Ap. Angl. i. t. xiii./. 19. 



d De Geer ii. t. ix./. 9. d. " Ibid. vi. t. u.f. 23. a a. 



f Plate IX. Fig. 19. p'". 



g Ibid. Fig, 7. and Plate XXII. Fig. 14. k". 



