Ii8 THE BOOK OF NATURE STUDY 



As to structure, the sexes differ from one another to a con- 

 siderable extent. Both are powerful-looking creatures, well 

 over an inch in length. They bear the three pairs of legs charac- 

 teristic of insects in general, but while the anterior pair are 

 short, clawed, and function for the most part only as grasping 

 organs, the others, especially the last pair, are flattened and serve 

 as swimming paddles. As in beetles in general, the body is covered 

 by the hard elytra or wing-covers, beneath which lie the mem- 



FiG. 54. Dyticus marginalis (female) and its larva 



branous wings, used only during flight, and at all other times 

 completely concealed beneath the elytra. In the male the elytra 

 are a dull black, bordered with a yellow streak, which extends 

 forward into the anterior region (thorax). The elytra are smooth 

 and polished. In the female the marginal streak is somewhat 

 less distinct, and in place of being smooth the elytra are deeply 

 grooved. Further, the male has the end joints of its anterior legs 

 curiously dilated and furnished with suckers. This modifica- 

 tion, like the roughened pad on the finger of the male frog, enables 

 the male to clasp its mate. 



The two most interesting points in regard to the beetles are, 

 however, certainly the adaptations which enable them to swim 



