CRUSTACEA GILLS 



327 



In the Isopoda the delicate-skinned lamellae of the pleopoda serve 

 for respiration, either both the lamellae of a foot or only the inner, the 

 outer one being hard-skinned and serving as a covering plate to protect 

 the inner one. 



The gills of the Stomatopoda (Squilld) are found as branched 



FIG. 228. ^4 and B, Gills of Astacus fluviatilis. In A the branchiostegite is removed. The gills 

 are seen in their natural position. In B the podobranchiae are cut off, and the outer arthrobranchise 

 turned back downwards. Twice the natural size, oj, a 2 , 1st and 2d antennae; 3, mandible ; ep 5 , 

 epipodite of the 2d maxilla ; 6, 1st maxillipede ; 7, 2d maxillipede ; 8, 3d maxillipede ; 9, forceps 

 (cut-off) ; 10-13, the 4 succeeding ambulatory feet ; pli, 1st pleopod ; a&i, a& 2 1st and 2d abdominal 

 segments ; pdb, podobranchige ; arl>, inner, orb 1 , outer arthrobranchise ; plb, pleurobranchise ; the 

 numbers attached show the appendages to which the gills belong, in order from before backward, 

 beginning with the anterior antenna as No. 1 ; gh, articular membrane between the body and basal 

 joint of the protopodite (after Huxley). 



appendages on the outer lamellae of the abdominal swimming feet 

 (pleopoda). The arrangement of the gills in Sirietta (Mysidce) 

 is similar; they here also occur in the males as appendages of the 

 pleopoda, but on their inner branches. 



The gills of the Amphipoda, Schizopoda (except the Mysidce), and 



