420 



NEUROPTERA 



the expansion of the wings is accompanied by frequent eleva- 

 tions and depressions of the body, and 

 occupies an hour or so ; the elongation 

 of the abdomen is not so soon completed, 

 and its brilliant colours do not appear 

 for several hours. 



The mouth of the nymph bears a remark- 

 able structure called the mask (Fig. 268). 

 It is apparently formed by a backward 

 growth of the bases of the labium and lingua, 

 a hinge being formed between the two at 

 the most posterior point of their growth. 

 The prolonged portions of these parts 



Fig. 267. Young nymph of are free : usually the mask is folded under 



Aeschna sp. (Cambridge) ^J^g J^^^^ ^^^^ ^^ ^^^^ ^^^ UnfoMcd and 



about iourtk moult. 



thrust forward, remaining then attached 

 to the head by means of the more anterior 

 parts of the lingua and by the maxillae, 

 the whole of the elongate apparatus be- 

 ing, when used, extended from this anterior 

 part of its attachment. The front parts 

 of the labium form a prehensile appa- 

 ratus armed with sharp teeth, so that the 

 structures make altogether a very effectual 

 trap, that can be extended in order to 

 secure the prey. 



The fact that the dragon-fly passes 

 suddenly, in the middle of its existence, 

 from an aquatic to an aerial life, makes 

 the condition of its respiratory organs a 

 subject for inquiry of more than usual 

 interest. Eeaumur was of opinion that 

 the nymph was, in spite of its aquatic 

 existence, provided with an extensive 

 system of stigmata or orifices for breath- 

 ing air ; this was, however, denied by 

 Dufour, and his opinion seemed to be 

 supported by the fact that other means 

 of obtaining air were discovered to exist 

 in these nymphs. The inquiries connected with the respiration 



Fig. 268. Under side of 

 head of Calepteryx virgo, 

 nymph, with mask un- 

 folded, a, Lingua ; h, 

 line from which the mask 

 swings ; c, line of doub- 

 ling up ; d, lower lip pro- 

 per ; e, articulated lateral 

 processes thereof. 



