WATEK-BEETLES. 



199 



of the species of the two families. But some of the Hydro- 

 philidce seem to have legs fitted for crawling over aquatic 

 plants rather than for swimming, while not a few of the 

 DytiscicLoe progress in the water like members of the Myd/ro- 

 pMlidcB. In distinguishing the different genera and species 

 of aquatic beetles it is necessary to pay attention to colour, 

 size, structure, and sculpture, but especially to the latter two. 



72— 



Fig. 130. Enlarged Outline op Male Water- Beetle (Dytiscus marginalis). 

 a. Antennae ; 6, Maxillary Palpi ; c. Bye ; d, Fore-Leg ; e. Thorax ; /, Middle 

 Leg ; g. Elytron ; A, Suture ; », Hind-Leg ; j, Claw ; k. Tarsus or Foot ; 

 I, Tibia or Shank ; m, Femur or Thigh ; n. First three Joints of Foot, 

 widened into a Plate possessing Suckers underneath. 



Certain DytiscidoB, such as Dytiscus marginalis, must not, 

 as every keeper of an aquarium, knows, be placed among fish 

 and other defenceless inhabitants of the water, but in separate 

 vessels, where they will be interesting and instructive. But 

 some of those beetles, if properly managed, can be with 

 advantage placed in the ordinary aquarium, for they will act 



