278 



INTRODUCTION TO ZOOLOGY 



CHAP. 



these " knives " can be swiftly whisked open, and the prey 

 caught with them and held, whilst the sharply pointed short 

 beak is rapidly put into action to suck up all the nutritive 

 juices of the victim. 



„ . At the end of the body are two grooved hair-like 



' projections, generally held together so that they look 

 _^ like one (Fig. 204, A). 



' The tube thus formed 



is at times pushed up- 

 wards through the sur- 

 face film of the water 

 into the air above, 

 and through it air is 

 drawn down into the 

 two spiracles situated 

 at the tip of the abdo- 

 men. Owing, however, 

 to its sluggish life, Nepa 

 only occasionally needs 

 to come to the surface 

 to get a fresh supply. 

 Eggs are 

 laid in the 

 water dur- 

 ing the summer ; each 

 is a small white oval 

 body with seven little 

 hairs projecting at one 

 end. In the oviduct 

 these eggs are in strings, 

 each circle of hairs form- 

 ing a cup into jyhich 

 the next egg fits; as 

 each egg is discharged, 

 however, the hairs be- 

 come recurved ; ^ a 

 single egg may be found adhering to a submerged water-weed 

 (Fig. 204, B). The function of the hairs may possibly be 

 to retain a supply of air for the developing egg.^ 



' See The Olassification of Insects, by J. 0. Westward (1840). 

 ^ Cambridge Natural History, vol. vi. p. 564. 



Reproduc- 

 tion. 



Fig. 204. — The Water Scorpion 

 (Nepa cinerea). 



A, Full-gro\vn insect swimming ; C, another waiting 

 tor its prey ; B, a larva hreathing at the siir- 

 face ; D, a single egg resting on a leaf. 



