FLIES FOR JUNE. 107 



conviction that neither the dark nor light Green 

 Ephemera lay eggs (being imperfect insects), but 

 that their metamorphoses, the Grey Drake and 

 the Dark Mackerel,^ lay eggs (whilst rising and 

 falling, &c.). This is an important fly on the 

 Blithe, and continues in season until the end of 

 June, and for part of July. 



' The egg of this fly and that of all the last metamorphoses 

 of the Ephemeridae, here spoken of, sinks to the bottom of the 

 water, and is there, in a few days, hatched into a white grig ; 

 this larva undergoes several transmutations before it becomes a 

 nympha, which, rising to the sm-face at its appointed season, 

 bursts the case or skin which encloses it (at the shoulders), 

 displays beautiful wings, quits its old husk, and, after the lapse 

 of a second or two, generally flies to the nearest terra firma, 

 where it remains in solitude and shelter (from the wind and 

 sunbeams) for about two days (see fig. 22, plate 11). It then 

 undergoes its last metamorphosis, and enters upon its iinago or 

 perfect state (see fig. 23), changing the whole of its envelopes, 

 even those of its fine tails and legs. The tails and the two fore- 

 legs of the male increase to about double their former length, 

 those of the female receive an accession of not quite one-third. 

 The colour is generally altered, the wings become shining and 

 transparent. The male carries two large stemmata upon his 

 head, and a pair of callipers at the end of his body, which two 

 peculiarities chiefly distinguish his appearance from the female. 

 He is also usually rather smaller than she is. He may be seen 

 merrily dancmg, as it were, up and down in the air in vast 

 crowds, frequently near a bush by the water side, whilst the 

 female is to be discovered busily employed rising and falling 

 and hovering over the water, and sometimes touching the 

 surface and making use of her long tails to spring up again. 

 She lays her eggs at this moment. 



The genus Potamanthus has three tails, or caudal setae ; 

 Baetis and Cloeon have only two of these appendages. 



