438 NEUROPTERA 



the mouth is atrophied in the imago, yet it is highly 

 developed in the nymphs. This is especially notable in the 

 case of the lingua or hypopharynx (Fig. 283) ; indeed Vayssiere 1 

 seems to incline to the opinion that this part of the mouth may 

 be looked on in these Insects as a pair of appendages of a head- 

 segment (see p. 96 ante), like the labium or maxillae. 



The life-history has not been fully ascertained in the case of 

 any species of may-fly ; it is known, however, that the develop- 

 ment of the nymph sometimes occupies a considerable period, and 

 it is thought that in the case of some species this extends to 

 as much as three years. It is rare to find the post-embryonic 

 development of an Insect occupying so long a period, so that we 

 are justified in saying that brief as may be the life of the may- 

 fly itself, the period of preparation for it is longer than usual. 

 Keaumur says, speaking of the winged fly, that its life is so short 

 that some species never see the sun. Their emergence from the 

 nymph-skin taking place at sunset, the duties of the generation 

 have been, so far as these individuals are concerned, completed before 

 the morning, and they die before sunrise. He thinks, indeed, 

 that individuals living thus long are to be looked on as Methuselahs 

 among their fellows, most of whom, he says, live only an hour or 

 half an hour. 2 It is by no means clear to which species these 

 remarks of Reaumur refer ; they are doubtless correct in certain 

 cases, but in others the life of the adult is not so very short, and 

 in some species may, in all probability, extend over three or four 

 days ; indeed, if the weather undergo an unfavourable change so 

 as to keep them motionless, the life of the flies may be prolonged 

 Jbr a fortnight. 



The life of the imago of the may-fly is as remarkable as it is 

 brief; in order to comprehend it we must refer to certain peculi- 

 arities of the anatomy with which the vital phenomena are con- 

 nected. The more important of these are the large eyes of the 

 males, the structure of the alimentary canal, and that of the 

 reproductive organs. We have already remarked that the parts 

 of the mouth in the imago are atrophied, yet the canal itself not 

 only exists but is even of greater capacity than usual ; it appears 

 to have much the same general arrangement of parts as it had in 

 the nymph. Its coats are, however, of great tenuity, and according 



1 Ann. Sti. Nat. Zool. (6) xiii. 1882, p. 113. 

 2 Reaumur, Mem. vi. 1742, p. 457. 



