VIII MAY-FLIES 287 



observe minute objects in the afternoon, though the 

 h'ght was not less bright than in the morning, for his 

 eyes were weary, and could no longer perceive 

 readily." 



Swammerdam's Life of an Ephemera follows : — 

 "The winged Palingenia (Fig. 91) is an Insect with 

 four wings, two small antennae, six feet, and two long, 

 hairy filaments, which stand straight out from the 

 hinder end of the body. It lives at most five hours in 

 the winged state. Every year it appears on the banks 

 of the Rhine, the Maas, the Waal, the Leek, and the 

 Yssel, appearing on the surface of the water about the 

 feast of St. Olof and St. John. The flies may be seen 

 in the air for three days together. Those which appear 

 on the first day die the same evening, and the same 

 thing happens on the second and third days. Then 

 a whole year has to elapse before they are seen again. 

 " When the female has emerged from the water 

 and cast off her skin, she passes the contents of 

 the double ovary into the water, but first she moves 

 to and fro on the surface of the water as if in sport, 

 and flits about with rapid exploring movements. 

 Immediately after the eggs are passed into the 

 water, they are fertilized by the male,^ which has 

 previously emerged and cast off a delicate mem- 

 braneous skin. The eggs, thus passed into the water 

 and fertilized, sink slowly, and are scattered over 

 the mud at the bottom of the stream. The form 

 of the eggs contributes to this mode of dispersal ; 



^ This is a mistake. The eggs are fertilized in other 

 Ephemera;, and no doubt in Palingenia too, while still in the 

 body of the female. 



