VI.] 



GILLS OF CRUSTACEA. 



223 



baken in and driven out, the more often is the animal 

 mechanically helped on its course. 



In no group are gills better or more characteristi- 

 3ally developed than in Crustacea, and in none do 

 we find better evidence of the association of locomotor 

 with respiratory activity. Among the lowest repre- 

 sentatives of the group (the BrancSiiopoda) a 

 number of the appen- 

 dages are nothing more 

 than broadened thin 

 plates within which 

 the blood circulates, 

 and outside of which is 

 the oxygenated water in 

 which they are bathed 

 (Fig. 96). 



In Squilla and its 

 allies branched tufts of 

 gill filaments are at- 

 tached to the abdomi- 

 nal feet. 



In the Decapoda, 

 such as the crayfish 

 or the lobster, the 



gills are outgrowths of the sides of the body wall, but 

 fcheir relation to the locomotor function is still well 

 marked ; in this group the gills are placed in a gill 

 chamber, which, as it is formed by lateral folds of the 

 dorsal integument, reminds us, so far, of the simpler 

 arrangements of the Branchiopod (Fig. 96 ; d) ; 

 these gills are set in three sets, the lowest of which 

 are (in the nomenclature of Huxley) podobranehs, 

 for they are attached to the basal joints of the appen- 

 dages (in the crayfish from the second maxilliped to 

 the penultimate thoracic appendage) ; the next set, 

 which are arranged in two rows, are called the 

 arthrobranchs, from the fact that they are attached 



Fig. 96. Transverse Section of 

 a Branchiopod, showing the 

 leaf-like (phyllopod) gills 

 (br'), which are appendages 

 of the body. 



c, Heart ; i, intestine ; n, ventral nerve- 

 cord ; d, fold of the iutegument. 

 (After Grube.) 



