AMPHIPODA. 493 



with an elongated abdomen, the three anterior segments of which bear 

 swimming feet, while the three posterior bear posteriorly directed 

 jeet adapted for springing (Fig. 304). The heart lies in the thorax, 

 and the eyes are not facetted. 



The Amphipoda are small animals, attaining only in rare cases 

 a length of several inches. They move in the water principally 

 by springing and by swimming. The " head " always includes 

 the first thoracic segment, and, in the Laemodipoda, the second 

 as well. It is some- 

 times small (Gam- 

 marina, Fig. 304), 

 sometimes large and 

 much swollen (Hy- 

 perina, Fig. 307), and 

 is generally sharply 

 distinct from the suc- 

 ceeding region. 



The two pairs of 



FIG. 304. Gammarus neglectus( = G. pulex) (after G. O.Sars), 

 antennae usually COn- with eggs between the brood lamellae (which are hidden by 



. , the coxopodites) on the thorax. A', A" the two antennae ; 



SISt OI a Short Strong I* to F? the seven pairs of thoracic appendages ; Kf 



, e . maxilliped ; Sf the first swimming foot of the abdomen. 



shaft and a long 



multiarticulate flagellum, which however may be more or 

 less rudimentary. The anterior antennae which are always 

 longer and are frequently beset with olfactory hairs in the 

 male, often bear a short accessory flagellum, a character not- 

 present in the Isopoda. In the Hyperina they are very short 

 in the female, though of considerable length in the male (Fig. 

 307). The posterior antennae are always simple, and are fre- 

 quently longer than the anterior ; in the male of the Hyperina 

 Anomala they are folded in a zig-zag fashion, and in the Coro- 

 phiidae are strong and pediform. In the female of Phronima 

 they are represented only by the basal joint (Fig. 307 a}. 



The mandibles are powerful biting plates with a sharp, usually 

 toothed edge, a blunt masticating process, and, usually, a three- 

 jointed palp. The bi-lobed anterior maxillae also have as a rule 

 a short two-jointed palp (Fig. 305), while the maxillae of the 

 second pair are reduced to two lamellae springing from a basal 



Bd. 1, Amphipoda, Christiania, 1890-95. Delia Valle, Gammarini del 

 Golfo di Napoli. Fauna and Flora Golf. Neapel, Monographic 20. 

 T. R. R. Stebbing, Amphipoda, 1. Gammaridae, Das Thierreich, Berlin, 

 1906. Compare also Bovallius and others. 



