170 



INSECTS. 



MALE OF COMMON MAY - FLT, 



Ephemera vulgata (nat. size). 



weather, however, they may sometimes be seen assembled together in swarms 

 about sundown, and engaged in their pastimes, which are continued till some time 

 after sunset. The peculiar up-and-down movement, which marks the flight of 

 some species, has been often observed ; and the mazy dance of the May-flies has 



been described by more than one author. In these 

 dancing assemblies the male insects always greatly 

 outnumber those of the other sex. The larvae of 

 the Ephemeridce live in water; a few kinds are 

 carnivorous, but most feed upon the minute vegeta- 

 tion scattered through the mud or covering stones, 

 and the larger aquatic plants. Many remain con- 

 cealed in the banks or under stones, while others 

 rove among water- weeds, and swim with celerity. 

 The larvae of some genera are found only in large 

 rivers. The eggs are, in some cases, deposited at the 

 surface of the water, and then sink to the bottom ; 

 but in others the female creeps into the water to 

 lay her eggs in patches on the under side of stones. 

 The eggs are exceedingly numerous, and vary in 

 shape according to the genus. The larvae cast their 

 skin several times ; they are at first without special 

 organs of respiration, but when they are about eight or ten days old tracheal gills 

 begin to appear and ultimately develop into forms, which vary somewhat in the 

 different genera. The gills are attached in pairs to the sides of some, or all, of the 

 first seven segments of the abdomen, in 

 some species standing out straight from 

 the sides, and in others turned over the 

 back. The mouth-organs of the larvae are 

 better developed than in the adult, the 

 mandibles being nearly always strong and 

 toothed, and sometimes giving off a tusk- 

 like process in front of the head. At their 

 transformation most May - flies do not 

 change directly from the larval form into 

 the imago, but first pass through a stage, 

 known as the subimago, in which they 

 have their wings expanded, and breathe 

 through the spiracles like the perfect 

 insect. In this form they are distin- 

 guished by the dulness of their integu- 

 ment, the shortness of the fore-legs and 

 tail-bristles, and the less prominent and a. may-fly at its final moult, with the imago 



, ,, ™ , . p ESCAPING FEOM THE SKIN OF THE SUBIMAGO. 



duller eyes. The subimago emerges from THE LARVA BEL0W= 



the larval skin at the surface of the 



water, and, after standing awhile upon the water, flies to a more convenient 



resting-place. At the next moult, which soon follows, the perfect insect makes 



