COLEOPTERA. 133 



figured on p. 128 lives in corn-fields, and has at different times committed great 

 havoc among crops wheat, barley, rye, etc., in various parts of Germany and Italy. 

 The Dytiscidce or carnivorous water-beetles, resemble the Carabidce in many 

 of their structural features, and differ chiefly in the modifications undergone to fit 

 them to an aquatic mode of life. Thus we find, as in the latter family, the 

 mentum is usually broad and deeply emarginate in front, the outer lobe of the 

 maxillae is two-jointed and palpiform, the antennae are moderately long and slender, 

 and the trochanters of the hind -legs are prominent. On the other hand, the 

 antennae are always smooth ; the head is broad and fits deeply into the prothorax, 

 while the latter is applied by a broad base against the elytra, so that the outline 

 of the body is continuous, and the general shape more or less oval ; the hind-legs, 



Dytiscus marginalia 1, Male ; 2, Female ; 3, Eggs ; 4, Pupa ; 5, Larva attacking a tadpole ; 6, Hydrocharis 

 caraboides ; 7, Its larva; 8, Acilius sulcatus, Female. (All nat. size.) 



which with their tibiae and tarsi flattened and furnished with rows of bristles, 

 are adapted to serve as oars in swimming, are somewhat longer than the other 

 legs, and come off from the body at a considerable distance behind them, while 

 their coxae appear as broad flat plates firmly joined to the metasternum, for parts 

 of which they might at first sight be very readily mistaken. The males may 

 be distinguished from the females by the shape of their fore-tarsi, in which the 

 first three joints are strongly dilated, and furnished underneath with sucker-like 

 hairs ; while in this sex also the back is generally smooth and glossy, the elytra 

 of the females frequently have a ribbed or corrugated surface. The Dytiscidce 

 seem especially fond of stagnant waters, and some of the species are common 

 objects in our ponds and ditches. They come to the surface when it is necessary 

 to take in a fresh supply of air beneath the elytra. These organs fit very closely 

 against the sides of the body, and so prevent the air from escaping while the beetle 



