326 THE RIVER-SIDE NATURALIST. 



others, again, swim and crawl freely among water-plants. 

 Probably some are carnivorous, either attacking other 

 larvae or subsisting on more minute forms of animal life ; 

 others perhaps feed on vegetable matter of a low type, 

 such as diatoms. 



" The winged insect differs considerably in form from its 

 aquatic state. The head is smaller, often occupied almost 

 entirely above in the male by the very large eyes, which 

 in some species are curiously double in that sex, one 

 portion being pillared, and forming what is termed a 

 turban. The mouth-parts are aborted, for the creature is 

 now incapable of taking nutriment, either solid or fluid. 

 The antennae are mere short bristles ; the proto-thorax is 

 much narrowed, the other segments greatly enlarged ; the 

 legs long and slender ; tarsi four or five jointed ; wings 

 carried erect anterior pair large, with numerous nervures 

 and abundant transverse reticulations ; the posterior pair 

 very much smaller, often lanceolate, and frequently abso- 

 lutely wanting. Abdomen consists of ten segments ; at 

 the end are either two or three long multi-articulate tails 

 (setae). In the male the ninth joint bears forcipated 

 appendages ; in the female the oviducts terminate at the 

 junction of the seventh and eighth ventral segments. The 

 sexual act takes place in the air, and is of very short 

 duration ; but is apparently repeated several times. 



" The number of described species is not less than 200, 

 spread over many genera." 



From the earliest times attention has been drawn to 

 the enormous abundance of some species of this family in 

 certain localities. Scopoli, writing more than a century 

 ago, speaks of them as so abundant in Carniola, that in 

 June twenty cartloads were carried away for manure. 

 Potymitarcys vtrgo, which though not found in England, 

 occurs in many parts of Europe (and is common in Paris), 

 emerges from the water soon after sunset, and continues 

 for several hours in such myriads as to resemble snow- 

 showers, putting out lights and causing inconvenience to 

 man and annoyance to horses by entering the nostrils. 

 In other parts of the world they have been recorded in 



