PHYLUM ARTHROPODA 



223 



Fig. 126. — Respiratory organs of Astacus fluviatilis. In A the gill-cover is removed 

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

 arthrobranchiae turned down. a lt antennule; a%, antenna; ab 1; first; ab 2 , 

 second abdominal segment; arb 7-12, inner arthrobranchiae; arb x . 7 12, outer 

 arthrobranchiae: ep. J, scaphognathite; plb. 11-13, pleurobranchiae ; pdb. 7-13, 

 podobranchs; pi. 1, first pleopod; 6-/3, thoracic appendages. (From Lang's 

 Comparative Anatomy, after Huxley.) 



lei canals in the stem — an external, the afferent branchial 

 vein, and an internal, the efferent branchial vein. 



According to their point of origin, the gills (Fig. 126) are 



