198 FBESH-WATEK AQ0AEIA. 



fish. Under such circumstances care should be taken to give 

 the beetles just enough food to satisfy them, but not enough 

 to ran the risk of corrupting the water, which ought always 

 to be, and will always be if the little necessary attention is 

 regularly given, perfectly clear. 



Ooleoptera are generally classified in four sections, accord- 

 ing to the number of the joints in their tarsi or feet : Trimera, 

 Tetramera, Heteromera, and Peniamera. Those possessing feet 

 having five joints are placed ia the Peniamera, which contains 

 most of the aquatic beetles. And to two families of this 

 section are confined nearly all the coleoptera with which we 

 have to do in this chapter, viz., the Dytiscidce and the 

 Hydrophilidce. The former family belongs to the sub-division 

 Sydradephaga (aquatic carnivorous beetles) of the tribe 

 Adephaga (predaceous beetles), and the species are therefore 

 carnivorous. The HydrophilidoB are herbivorous, and are 

 members of the only family of the tribe Palpicornia 

 (possessing long and slender palpi). 



The Dytiscidce differ from the Hydrophilidce chiefly in the 

 formation of their antennsB and palpi (Fig. 130). In the 

 former the antennse are slim and elongated, and in the latter 

 they are short and clubbed. But in the SydrophiUdce the 

 maxillary palpi are long and slender, and are much more 

 conspicuous than their antennse, which are often placed close 

 to the body, out of sight ; while the palpi of the Dytiscidce 

 are quite small when compared with the length and 

 prominence of their antennae. There is a difference also in 

 the formation of the legs of the two families. In the 

 Dytiscidce the legs are especially adapted for swimming, the 

 fore and middle pairs of legs being placed closely together, 

 while the hind-legs are placed at some little distance from 

 them to allow of plenty of room for the swimming movement. 

 But in the Hydrophilidce the three pairs of legs are almost 

 equal distances apart. When swimming, the hind-legs of the 

 Dytiscidce move together, while those of the Hydrophilidce 

 move alternately. The former may be said to swim somewhat 

 similar to a frog, and the latter like a dog. This difference 

 in the manner of swimming is more or less apparent in most 



