I AQUATIC BEETLES 51 



head is deeply sunk into the thorax, and does not 

 break the outline. A body so shaped is obviously 

 well fitted for rapid movement through the water, 



FIG. 9. Dytiscus marginalis, female. 



as well as for easy entrance into narrow spaces. 

 Dytiscus marginalis takes its name from the yellow 

 stripe, which runs along the border of the thorax, the 

 outer edge of the wing-cover, and the front of the 

 head. Many other species of the genus Dytiscus are 

 ornamented in a somewhat similar way. 



The mouth-parts are adapted to a predatory life, 

 for the full-grown Beetle is not less voracious than 

 the larva. The mandibles are no longer slender 

 and perforated, but stout and double-toothed. The 

 antennae are rather long and slender, and the 

 compound eyes large. 



E 2 



