154 ANIMAL BIOLOGY 



that it is largely composed of numerous slender 

 divisions, called the gill filaments. 

 Make a sketch of the leg ( X 2) with the gills at- 

 tached and label gill filaments. 



4. The gills are furnished with numerous minute thin- 



walled blood vessels and the blood in them is 

 separated from the water only by a thin mem- 

 brane. The blood flows into the gills from all 

 parts of the body by one set of blood vessels 

 and leaves the gills by another. Bearing in 

 mind that breathing is essentially the same in 

 animals as in plants (P. B., 82), 



a. What gas will the blood bring from the body to 



be given off in the gills in the process of breath- 

 ing? 



b. What gas is taken up by the blood in the gills to 



be carried around the body? 



c. How are the gill filaments (as stated above) fitted 



by structure to permit this interchange of 

 gases ? 



d. How are the delicate gill filaments protected from 



injury? 



5. If the same water remained on the gills for some time, 



what changes in the relative, amounts of oxygen 

 and carbon dioxid in the water would occur? 

 Why, then, is it necessary that a current of 

 water should pass over the gills? 



6. Do currents of water pass through the gill chamber f 



- Demonstration. 



Inject some harmless coloring matter, such as 

 powdered carmine in water, into the posterior 

 end of the gill chamber. Place the crayfish 

 again in water. 



a. State what was done in this experiment. 



b. Give your observations and conclusion. 



c. What will the incoming current of water bring 



to the gill filaments ? 



d. What will the current of water carry away from 



the gill filaments ? 



