PHYLUM ARTHROPODA 



223 



FIG. 117. Respiratory organs ot'AstacuS fluviatilis. In A the gill-rover is removed 

 and the gills undisturbed ; in B the podobranchiae are removed and the outer 

 arthrobranchiae turned down. a\. antennule ; a^. antenna ; ab\. first, ab-2. 

 second abdominal segment ; arb.f 7.2, inner arthrobranchiae ; arb.' ' j 12, outer 

 arthrobranchiae ; ^/.J, scaphognathite ; plb. u 13, pleurobranchiae ; pdb. 7 fj, 

 podobranchs ; pi. /, first pleopod ; 6 13, thoracic appendages. (From Lang's 

 Comparative Anatomy, after Huxley.) 



