2 I 3 COLEOPTERA 



suckers communicate with a sac in the interior of the foot contain- 

 ing fluid, which exudes under pressure. As the portions of the 

 skeleton of the female on which these suckers are brought to 

 bear is frequently covered with pores, or minute pits, it is prob- 

 able that some correlation between the two organisms is brought 

 about by these structures. The females in many groups of 

 Dytiscidae bear on the upper surface of the body a peculiar 

 sculpture of various kinds, the exact use of which is unknown ; 

 in many species there are two forms of the female, one possessing 

 this pecuHar sculpture, the other nearly, or quite, without it. 

 The larvae of Dytiscidae differ from those of Carabidae chiefly 

 by the structure of the mouth and of the abdomen. They are 

 excessively rapacious, and are indeed almost constantly engaged 

 in sucking the juices of soft and small aquatic animals, by no 

 means excluding their owa kind. The mode of suction is not 

 thoroughly known, but so far as the details have been ascertained 

 they are correctly described, in the work on aquatic Insects, by 

 Professor Miall, we have previously referred to ; the mandibles 

 are hollow, with a hole near the tip and another at the base, and 

 being sharp at the tips are thrust into the body of a victim, and 

 then by their closure the other parts of the mouth, which are 

 very beautifully constructed for the purpose, are brought into 

 fitting mechanical positions for completing the work of emptying 

 the victim. Nagel states that the larva of Dytiscus injects a 

 digestive fluid into the body of its victim, and that this fluid 

 rapidly dissolves all the more solid parts of the prey, so that the 

 rapacious larva can easily absorb all its victim except the 

 insoluble outer skin. The abdomen consists of only eight 

 segments, and a pair of terminal processes ; the stigmata are all 

 more or less completely obsolete — according to species — with the 

 exception of the pair on the eighth segment at the tip of the 

 body ; the terminal segments are frequently fringed with hairs, 

 that serve not only as means of locomotion, but also to float . the 

 pair of active stigmata at the surface when the creature rises to 

 get air. Although the larvae of Dytiscidae are but little known, 

 yet considerable diversity has already been found. Those of 

 Hyfliydrus and some species of Hydro2:)orus have the front of the 

 head produced into a horn, which is touched by the tips of the 

 mandibles. 



Dytiscidae are peculiar inasmuch as they appear to flourish 



