IV] 



FROM WATER TO AIR 



33 



life-history of Chloeon. In the second year of aquatic 

 life wing-rudiments (fig. 9 a) are 

 visible, and the larva becomes a 

 nymph. When the time for the 

 winged condition approaches the 

 nymphs leave the water in large 

 swarms. The vivid accounts of 

 these swarms given by Swam- 

 merdam (1675), de Reaumur 

 (1742) and other old-time obser- 

 vers are available in summarised 

 form for English readers in 

 Miall's admirable book (1895). 

 May-flies are eagerly sought as 

 food by trout, and the rise of the 

 fly on many lakes ushers in a 

 welcome season to the angler. 



The nymph-cuticle opens and 

 the winged insect emerges. But 

 this is not the final instar; may- 

 flies are exceptional among in- 

 sects in undergoing yet another 

 moult after they have acquired 

 wings which they can use for 

 flight. The instar that emerges 

 from the nymph-cuticle is a sub- 

 imago, dull in hue, with a curious 

 immature aspect about it. A few 



c. i. 



Fig. 9. Nymph of May- 

 fly (Chloeon dipterum) 

 showing on right side 

 wing-rudiment (d), on 

 left tracheal gills (b). 

 Magnified 4 times. 

 [Feelers and legs are 

 cut short.] From Miall 

 and Denny after Vays- 

 siere. 



