THE LOBSTER. 



141 



pericardium by straps, or muscles. The heart is not 

 hollow inside like a bag, but is nearly all filled up by 

 its own thick, spongy walls. There are six openings 



Fig. 122. 



Heart-sac, or 

 Pericardium. 



-Muscle. 



The Lobster's Heart slung in its Sao by Straps, or Muscles. 



leading into the one room, or ventricle, from the outer 

 sac, or pericardium. These openings, or doors, are 

 guarded by little valves, which allow the blood to pass 

 inward, but prevent its return. The ventricle gives off 

 six tubes, or arteries, five in front and one very large 

 one behind (Fig. 123) ; these arteries divide into small- 

 er ones (capillaries) which carry the blood all over 

 the body. While the blood is passing slowly through 

 the fine hair-tubes (capillaries) it gives up its oxy- 

 gen and nutritious matters to feed the body, and re- 



