284 



COLLEGE ZOOLOGY 



Respiration. — Between the branchiostegites and the body- 

 wall are the branchial chambers containing the respiratory organs, 

 the gills. At the anterior end of the branchial chamber is a 

 channel in which the scaphognathite of the second maxilla (Fig. 

 201, A, 6) moves back and forth, forcing the water out through 

 the anterior opening. Fresh water flows in through the poste- 

 rior opening of the branchial chamber. 



Gills. — There are two rows of gills; the outer, podobranchice, 

 are fastened to the coxopodites of certain appendages (see Table 

 X) and the inner double row, the arthrobranchicB, arise from the 

 membranes at the bases of these appendages. In Astacus there 

 is a third row, the pleurobranchia, attached to the walls of the 

 thorax. The number and arrangement of these gills are shown 

 in Table X. Each gill possesses a number of gill filaments. 



TABLE X 



THE NUMBER AND POSITION OF THE GILLS OF THE CRAYFISH 



(Cambarus) 



Excretion. — The waste products of metabolism are taken 

 from the blood by a pair of rather large bodies, the "green 

 glands " (Fig. 202, 40) situated in the ventral part of the head 



