XVIII 



DRAGON-FLIES 



411 



the action of the mouthpieces by actual observation. For the 

 purpose of securing the prey a moutli that can change its 

 capacity to a considerable extent and with rapidity is a desider- 

 atum, and these qualities are present in the mouths of those 

 Libellulidae that capture their prey while hawking. The upper lip 

 is very mobile, is pendent, and closes the mouth above, while the 

 lower lip entirely closes the under part by means of two mobile 

 plates ; these in some forms (Libellula) meet together in the 

 mesial line, while in others a third plate separates them in the 

 middle (Fig. 26 1, B, li). These plates are, according to Gerstaecker's 

 view,^ portions of the much changed labial palpi, the part that 

 separates them in Aeschna being the inner lobes of the labial max- 

 illae ; in Libellula, wdiere the dilated and valve-like joints of the 



Fig. 261. a, Maxilla 

 of Libellula quad- 

 o'imacidata ; B, la- 

 bium of Aeschna 

 grandis. p, p'. 

 Palpus ; a, ter- 

 minal spine of 

 palpus ; c, cardo ; 

 ^jStipes ; s,squania ; 

 le, outer lobe of 

 maxilla, partly 

 covered by, li, 

 inner lobe ; in, 

 mentum ; r, inter- 

 vening lobe. (After 

 Gerstaecker. ) 



palpi meet in the middle line, the labial lobes remain small and are 

 overlapped by the dilated portions of the palpi. The maxillae 

 proper (Fig. 261, A) are less peculiar, their chief character being 

 that the inner and outer lobes are not separated, and that the palpus 

 is of only one joint. Some entomologists take, however, another 

 view of this structure, looking on the palp-like outer part (^ of 

 our figure) as the true outer lobe of the maxillae, the palpus 

 proper being in that case considered to be entirely absent. Tlie 

 mandibles are very powerful, and armed witli largely developed 

 teeth. In the interior of the mouth there is a large, free, semi- 

 membranous lingua, the posterior part of its delicate inferior 

 lamina being connected with the mentum ; the upper lamina of 

 the lingua is stronger and is pilose. The antennae of the dragon- 

 flies are always small, and consist of two stouter joints at the 



^ Festschrift Gcs. naturf. Freunde Berlin, 1873. 



