280 



INTRODUCTION TO ZOOLOGY 



CHAP. 



at the end of each stroke. The body is long and narrow, the 

 ventral surface flat, and the back strongly keeled, giving it 

 a superficial resemblance to a boat, though the body is blunt 

 in front and pointed behind. The colour is a pretty bluish- 

 grey with some black on the back. The first segment of the 

 thorax is very highly polished, and the glossy triangular plate 

 of the second segment (the scutellum) is also large and con- 

 spicuous, as is usually the case in Rhyncota. The wings are 

 well developed, and the insect often flies in the evening with 





3. 



f\. 



FIG. 206. The Water Boatman (Notonecta glauca}. 

 A, Larva swimming ; P>, back view of an adult Notonecta ; C, ventral VJCAV. ( x 1J.) 



a strong swift motion and a humming sound. When at 

 rest, the horny base of the fore wing covers its membranous 

 portion and also the very delicate second pair of wings. The 

 under surface of the body, i.e. the side which floats upper- 

 most, is covered with small hairs, and glistens like silver in the 

 water owing to the air which is entangled amongst the hairs. 

 This film of air keeps the body, even when submerged in the 

 water, completely dry, and also makes it buoyant, so that, 

 when at rest, it floats to the surface with the tail projecting, 

 and opens up fresh communication with the atmosphere. 

 The air-film over the body and below the wings is thus 

 renewed, and fresh air is taken in by the spiracles, which lie 

 just below the outer horny edge of each front wing. In 

 order to remain below the water without moving, the insect 



