A 



PHYLUM ARTHROPOD A 



223 



<«#a (Bin at?., al6 a aifSj <itBj 

 'pCg, J " "' ' 



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

 and the gills undisturbed; in B the podobranchia: are removed and the outer 

 arthrobranchia: turned down. a i , antennule; a.,, antenna; ab x , first; ad 2t 

 second abdominal segment; arb. y-12, inner arthrobranchia;; arl\. J-12, outer 

 arthrobranchia;: ef>. j, scaphognathite ; fib. 11-13, pleurobranchise; pdb, 7-13, 

 podobranchs; pi. 1, first pleopod; 6-13, 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 



