300 NATURAL HISTORY OF AQUATIC INSECTS CH 



that the winged fly suddenly darts out from the midst 

 of the water. It is possible to observe what is taking 

 place by going on the stream in a boat, catching with 

 the hand larvae which are about to emerge, and 

 slightly pressing the thorax so that they cannot 

 disengage themselves from the larval skin. 



" How, we may ask, are the wings expanded with 

 such speed ? We might suppose that they are pro- 

 vided, like the wings of Earwigs, with muscles, which 

 can suddenly expand the wings, or at pleasure fold 

 them up again within their narrow r sheaths. But the 

 wings of the Palingenia are not provided with 

 muscles, and it appears that they are expanded by 

 sudden injection of blood from the heart. If the 

 wings at the time of emergence are wounded, they 

 bleed freely. Air injected into the air-tubes may also 

 help to render them stiff and dry. If the wings of a 

 larva ready for emergence are cut off and thrown 

 upon the surface of water, they can be seen to expand, 

 though detached from the body. 



" When the Palingenia has quitted the water it 

 makes its way at once to some place where it can 

 settle, and then it immediately casts a second very 

 delicate and transparent skin, which covers the whole 

 body. This second moult, following so rapidly upon 

 the former one, does not materially change the shape 

 or appearance of the Insect. 



" At the time that the Palingenia leaves the water, 

 the external form of the body undergoes conspicuous 

 change. The gills are completely cast, leaving only 

 small rudiments on the sides of the abdomen. At 

 the same time the jaws, the larval feet, and the 



