114 CRUSTACEA. 



times, as in Chondr acanthus, the foot-jaws, which 

 are stout and armed with strong hooks, are inserted 

 into the victim. In the Lerneop.odce we find two 

 long arms proceeding from the thorax, which, 

 meeting at their tips, are united, and bear a knob 

 or button, which, being thrust into the flesh, main- 

 tains the hold. In Achtheres, a genus that infests 

 the Perch of our rivers, the button at the tip of 

 the united arms is dilated into a bell-shaped 

 cupping-glass, beset within its rim with recurved 

 hooks. In Lerneonema and its fellows, the whole 

 head is inserted ; and this, being furnished with a 

 prong on each side curving backwards, ^ forms a 

 powerful anchor, by which the parasite is firmly 

 moored to its hapless prey. Finally, in Lemea 

 (which, with its long, unsymmetrical, and strangely 

 twisted body, is perhaps the most uncouth of all), 

 the processes of the head are irregularly branched, 

 affording the same sort of hold that a tree obtains 

 in the soil by its spreading roots. 



The Entomostraca do not present us with any 

 contrivances so strange as these, but the appear- 

 ance of many of them differs widely from that of 

 the more familiar Crustacea. Their limbs are 

 generally tipped and otherwise furnished with 

 tufts of plumose bristles, some of which appear to 

 answer the purpose of breathing, as well as motion; 

 they commonly have but a single eye, of large size 

 and brilliant colour, in the centre of the forehead ; 

 and the carapace is often very large, almost or 

 quite enveloping the animal. In the Tribe Ostra- 

 coda this is formed of two large convex plates, 

 closely like the valves of a bivalve shell, united 

 over the back by a hinge, but gaping beneath for 

 the protrusion of the feet. In the Tribe Cladocera 



