EXTERNAL ANATOMY OF INSECTS. 471 



to be divided into two by a membranous partition, and 

 to contain in the upper cavity a small cylindrical tube, 

 which seemed to be a trachea a . To animals that are 

 without lungs, and breathe by trachece, suction must be 

 performed in a very different way from what it is by 

 those that breathe by the mouth : and as in the very ex- 

 tended organs in question the fluid has a long space to 

 pass before it reaches the pharynx, in some way or other 

 these lateral tubes may have the power of producing a 

 vacuum in the middle tube, and so facilitate its passage 

 thither.- We see, in the antlia, that the maxillae receive 

 their vast elongation at the expense of all the other or- 

 gans, except the labial palpi. 



iv. Mostrulum h . — An animal very annoying to us af- 

 fords the type of the next kind of imperfect mouth — I 

 mean the Jlea. Its oral apparatus, which I would name 

 rostrulum, appears to consist of seven pieces. First are a 

 pair of triangular organs, the lamina, which together 

 somewhat resemble the beak of a bird, and are affixed, 

 one on each side of the mouth, under the antennae: these 

 represent the mandibles of a perfect mouth c . Next, a 

 pair of long sharp lancets (Scalpella), which emerge from 

 the head below the laminae: these are analogous to max- 

 illce^'. a pair of palpi, consisting of four joints, are at- 

 tached to these near their base e , which of course are 

 maxillary palpu And lastly, in the midst of all is a 

 slender setiform organ (ligula), which is the counterpart 

 of the tongue f . Rosel, and after him Latreille, seem to 



a N. Diet. d'Hist Nat. iv. 253. 



b Plate VII. Fig. 8. c, d', e , h". c Ibid. c'. 



d Ibid. d'. E Ibid. h". ' Ibid. e. 



