68 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



implies, the function of respiration undertaken by some 

 of the appendages ; the body is often provided with a 

 fold (Fig. 28 ; 1, 2), which is derived from the dorsal 

 portions of the anterior metameres, and forms a back- 

 wardly-directed free carapace. Such are Apus and 

 Daphnia ; Nebalia forms a link of connection with the 

 Malacostraca. 



Fig. 28. Various Entornostraca. 



1, Daphnia pulex; 2, Candona hispida; 3a, adult female of Cyclops quadri- 

 cornis ; b, c, d, larvre ; 4, Cetochilus septentriormlis ; 5, Sap'phirina ovato 

 lanceolata ; 6, Nicothoe astaci (parasitic on the gills of the lobster); 7, Nau- 

 plius stage of copepod. (From Woodward.) 



2. The Copepoda have a small stout body, 

 covered by a carapace ; one pair of the antennae are 

 large and oar-like (Fig. 28 ; 3a), and retain the primi- 

 tive locomotor function that they had in the 

 nauplius stage. Cyclops and Cetochilus are free- 

 swimming forms ; some, like Sapphirina (Fig. 28 ; 5) 

 are temporary parasites ; others, like Nicothoe (Fig. 28; 

 6), which lives on lobsters and crayfishes; Dichelestium, 

 which is found on the sturgeon, and Lernsea, which lives 

 on the cod and other fishes, are still more modified ; 



