358 



THE INVERTEBRATA 



mxp' 



thA. 



'a A 



Fig. 263. A, Bopyrus fougerouxi: a female in ventral view. From the 

 Cambridge Natural History, after Bonnier, mxp. maxilliped; th.^, fourth 

 thoracic limb (third leg) ; 00. oostegite ; (^,male attached to female. B, Crypto- 

 niscus pagiiri: ripe female stage in ventral view. After Fraisse. M. mouth; 

 op. bd. line along which brood pouch will open; rsp. one of two openings 

 through which a respiratory current passes to and from brood pouch. 



Order AMPHIPODA 

 Peracarida without carapace ; with sessile eyes ; the body usually com- 

 pressed; no antennal exopodite; the thoracic limbs without exo- 

 podites, the first pair modified as maxillipeds, the remainder of more 

 than one form, the second and third usually prehensile; the pleopods 

 when fully developed divided into two sets, the first three pairs with 

 multiarticulate rami, the last two resembling the uropods, which do 

 not form a tail fan. 



We will take as an example of this order Gammarus (Figs. 264-266), 

 of which closely related species occur in Britain in fresh waters and 

 between tidemarks in the sea. The body of this animal is compressed 

 and elongated, with the ist thoracic somite fused to the head and no 

 sharp distinction between the thorax and abdomen, which are of 

 nearly equal length. At the sides of the head are pleural plates. The 

 pleura of the thorax are short; but large, hinged coxal plates on the 

 legs take their place. All the segments of the abdomen are free. The 

 telson is deeply cleft. The antennules have two flagella; the uni- 

 ramous antennae are much like those of Ligia. The mandibles have 

 the same parts as those oi Ligia ^ with a palp. The maxillules, maxillae, 



