POND LIFE. 



129 



of the body is furnished with a pair of long, slender, 

 horny appendages. Each of these is grooved on the 

 inner side, so that when they are held together they 

 form a tube through which air can be drawn. They 

 are represented in this position in the figure of Nepa 

 and separate in that of Ranatra. 



Another interesting feature in the structure of 

 water-scorpions is the form of the fore legs. These 

 are fitted for grasping, and are of such form that 

 each is a complete organ by itself. The coxa is long 

 (in the case of Ranatra it is very long, so that it ap- 

 pears like a femur), and the femur is furnished with 

 a groove into which the tibia and tarsus fit like the 

 blade of a pocket-knife into the handle. 



The resemblance in form to a scorpion is quite 

 striking in the case of Nepa (Fig. 102), but it is much 

 less so with Ranatra. 



If you succeed in obtaining water-scorpions, keep 

 them in an aquarium and observe their habits. Study 

 their method of obtaining air, the way in which they 

 seize their prey, their modes of locomotion, and any 

 other features of their life history that you can observe. 



The body of Nepa is very flat, enabling the insect 

 to hide beneath stones and rubbish on the bottom of 

 ponds. With Ranatra the slender form of the body 

 and the dirt with which it is usually covered causes 

 the insect to resemble a dirty stick. This resem- 

 blance doubtless aids the insect greatly in the cap- 

 ture of its prey. 



Adult water-scorpions have well-developed wings 

 which reach nearly to the end of the abdomen ; if 

 you find wingless individuals, or some with short 

 wing-pads, label them as nymphs. 



