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 and 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 are drawn in is 



FIG. 5. Head of larva of Dytiscus, from beneath. 



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

 hairs." l 



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, 2 but little by little devour all its 



1 Bibha Nat urcz, Vol. I. p. 325. 



2 Cloporte ; the word is elsewhere applied to an Asellus. 



