32 PRACTICAL ZOOLOGY. 



with water. Pin it to the bottom, through the telson, and 

 through the big claws. Observe a groove, curving 

 lengthwise, 011 each side of the back of the carapace. 

 Insert the point of one blade of the scissors under the 

 hinder edge of the carapace at one side. Cut forward, a 

 little outside the above-noticed groove, to the groove 

 which separates the head from the thorax. Break away 

 the whole of the side of the carapace. Push the gills 

 downwards, and cut them off at their point of attach- 

 ment below. 



Observe the thin wall separating the cavity in which 

 the gills were, the gill-chamber, from the body cavity. 

 Clear away the other side likewise. With the forceps 

 pick away the narrow cover of the body cavity carefully, 

 as the heart lies just under the carapace. 



1. The heart is an oblong, whitish body. Look for holes 

 in its upper surface, and for small white tubes running 

 forward from it toward the head. With the forceps 

 gently lift the hinder end of the heart; note its 

 angularity. 



There are two holes in the top of the heart, two 

 beneath, and one on each side. These holes are 

 guarded by lip-like valves on the inside, so that when 

 the heart contracts, the blood cannot flow out through 

 the holes, but is driven out through the arteries to the 

 various parts of the body. From the different parts 

 of the body the blood goes to the gills. Returning 

 from the gills, it enters the cavity in which the heart 

 lies, the pericardial cavity. As the valves at the 

 openings of the heart open inward, the blood readily 

 flows into the heart when it expands. 



