222 BEANCHIOPODA. 



extent, the wood appearing ploughed up, so to speak, rather than 

 burrowed into. Upon the whole, Chelura would seem to be a more 

 destructive creature than even Limnoria. 



The Fresh- water Shrimp (Asellus) is met with abundantly in our 

 ponds and streams. It walks with difficulty, but swims rapidly, 

 lying on its side. The eggs of the female are carried in a bag 

 attached beneath the body. They are very voracious, and as they 

 eagerly devour all dead animal substances, are beneficial agents in 

 purifying the water. 



The Wood Lice (Oniscus) are terrestrial in their habits. They are 

 to be met with everywhere in dark and damp situations, such as 

 caverns, cellars, in holes in old walls, under stones or beams of wood, 

 window-sashes, and similar localities. They feed entirely upon 

 decayed animal and vegetable substances, and never leave their 

 retreat, except in rainy or damp weather. 



ENTOMOSTRACA.* 



SIXTH ORDER OF CRUSTACEA. 



BRANCHIOPODAI (GUI-footed Crustaceans). 



Any one who lias ever examined a phial of water 

 taken from any ditch, must have observed in it a 

 variety of tiny, but most indefatigable, little crea- 

 tures, that move actively by short jerks, or dart to 

 and fro witH a rapidity that the eye can scarcely 

 follow ; the jerking ones (Fig. 170, 3) are species of 

 Daphnia ; the more fleet, darting forms are of the 

 genus Cyclops (Fig. 170, i ) ; and another tribe, still 

 more varied in shape, that keep chiefly near the bot- 

 tom, and creep nimbly, more than they swim, are the 

 Cyprides (Fig. 170, 2) : all these, under a microscope, 

 are exceedingly beautiful. Some have their bodies en- 

 closed between two delicate plates, united above the 

 back, and resembling a bivalve shell ; this shell is 

 usually more or less transparent, and delicately 

 tesselated, or marked with an intricate network of 

 raised lines. The antennae are often curiously 

 branched, and appear to be used as oars. It is a re- 



* evrofjios, entomos, an insect; oa-rpaKov, ostrakon, a shell i.e., 

 insects with shells. 



f /8pa*/x*a, branchia, gills ; -rrovs-jroSos, pous-podos, a foot so called 

 because their feet perform the functions of gills. 



