I AQUATIC BEETLES 43 



stomach, especially if the victim has red blood. . . . 

 When the mandible is examined by the microscope, 

 we see that it runs out into a sharp point artd is some- 

 what curved. In cross section it appears sharp-edged, 

 flattened on both sides, and convex along its outer 

 border. The opening by which fluids arc drawn in is 



Fig. 5. — Head of larva of Dytiscus, from beneath. 



near the tip, and forms an elongate slit, fringed by fine 

 hairs." ^ 



De Geer tells us that on examining the mandible 

 by the microscope he found the slit described by 

 Swammerdam. " But," he continues, " is there no 

 other mouth ? I believe that there is, and that this 

 mouth lies between the lips (labrum and labium). As 

 proof of this I have seen a Dytiscus larva not only 

 suck a Crustacean," but little by little devour all its 



' Biblia Natures, Vol. I. p. 325. 



^ Cloporte \ the word is elsewhere applied to an Asellus. 



