i8 



enters the heart by six openings in its walls, each 

 guarded by a pair of valves which close when the 

 heart contracts, and prevent the blood from returning 

 to the pericardium. 



The venous channels which convey the blood 

 back to the heart are so arranged that most of the 



FIG. 7 GILLS OF THE LOBSTER, EXPOSED BY CUTTING AWAY THE 

 SIDE-FLAP OF THE CARAPACE (BRANCHIOSTEGITE) 



blood passes first through the gills, for the purpose 

 of respiration, before it reaches the heart and is 

 again distributed through the body. These gills, 

 as already mentioned, lie in the two branchial 

 chambers under the side-flaps of the carapace 

 (Fig. 7), and are attached, some to the epipodites 

 of the thoracic limbs (as described above), and 

 some to the soft membrane of the joints between 

 the limbs and the body; while others are attached 



