370 LAKES AND STREAMS 



thread-like appendage protruding from the surface. The larvae which emerge 



from the eggs have only rudimentary wings, but are otherwise similar to the 



parent insects, except with regard to their breathing-apparatus. 



An aquatic insect which, if carelessly handled, makes its 

 Water-Boatman. *• . ' 



displeasure known by a painful sting, and has therefore been given 



the name of the water-bee, is the water-boatman (Notonecta glauca), a creature 



which always swims on its back, and is coloured accordingly, the under surface 



being dark, while, owing to the air-bubbles which adhere to it, the surface of 



the back when under water appears white. These insects swim well, using as sculls 



the long and powerful hind-legs, which are furnished with hairs ; while the front 



Stt *)-\V^ 



THE WATEP.-SCOnPIOjf. 



and middle pair serve for seizing and holding the prey. In order to inhale the air, 

 water-boatmen project the hind end of the body out of the water in the same way as 

 brown water- beetles. The breathing-apertures situated in this part are, however, 

 small, while the larger ones, which are provided with delicate, protecting hairs, and 

 probably serve more especially for the purpose of respiration, are placed some way 

 off, on the side of the thorax, at the root of the wings. Others, again, are situated 

 1 lei ween the middle and back of the thorax, on the edge of the under part of the body, 

 To these apertures air is conducted in a peculiar manner. The abdomen is ridged, 

 and raised on the edges so as to form two shallow longitudinal grooves on the sides, 

 covered with a sort of roof formed by two rows of hairs, one of which extends 

 along the outer edge of the under side of the body, the other down the middle: the 

 grooves thus forming channels along which the air is conducted from the hind- 



