490 ZOOLOGY. 



apis, the branchipes, the daphnise. It is to this group that 

 the trilobites seem to have belonged : marine animals, whose 

 fossil remains are found in the most ancient strata of the 

 globe, but of which there exists not at present any living 

 representative in the seas. 



577. The entomostraca are also formed only for 

 swimming, and in youth they all possess a certain number of 

 rigid double-oared limbs ; but in the adult state they are 

 mostly sedentary, and then the body becomes deformed in a 

 very singular manner ; in general they have but a single eye, 

 placed in the middle of the forehead, and their respiration 

 seems to take place over the whole surface of the body. 



Fig. 520. Cyclops ; one of the Entomostraca. 



578. t Some, called copepoda, are always very active, and 

 possess large antennae and a masticatory apparatus ; these are 

 the cyclops, or monocules (Fig. 520).* 



579. Others live as parasites on fishes, Crustacea, &c., 

 and have the mouth elongated in the form of a proboscis or 

 beak, armed with style-formed appendages adapted to pierce 

 the integuments of the animals whose juices they suck. They 

 have been divided into the siphonostoma and the lernsea; the 

 first have always swimming limbs, ahd attach themselves by 

 means of limb-jaws Having the form of hooks ; the second, on 

 reaching the adult age, present no longer any traces of loco- 

 motory organ's, and have often been confounded with the 

 intestinal worms.f 



580. It is also in this division of the entomostraca that 



* The Entomostraca play an important part in the great economy of 

 nature. They form the especial food of many valuable fishes of the family 

 salmonidae, clupeidae, and coregoni; and it is evident, from the remains in 

 the limestone strata, that they abounded, and were perhaps of a larger size 

 generally, in the seas and fresh waters of the ancient world. E. K. 



t A species of lernaea attacks the gills of the salmon during its residence in 

 fresh waters, but seems to perish when the fish return to the sea. B. K. 



