ANIMALS WITH JOINTED LEGS— THE ARTHROPODS 



185 



ins - " for crawciads with a piece of bacon tied on a piece of string. The 

 animal will grab the bacon with its pincers and, with just the right de- 

 gree of pull on the string, will hold on until it is out of the water. Their 

 abdomens or "tails" contain edible white meat, and they are often caught 

 in large numbers for human consumption. 



Photo by Winchester 

 Fig. 13.3. Crayfish burrows. When the water level is not far under the surface, 

 crayfish sometimes build burrows down to the water. In some sections of the country 

 this creates quite a problem by weakening and allowing leakage from dams and levees. 



Epipodite 



Protopodife 



Exopodite 

 -Endopodite 



Fig. 13.4. 



Diagram showing the location of the parts of appendages of the crayfish. 

 Not all appendages have all of the parts listed. 



The appendages of the crayfish are diversified to meet a number of 

 different needs, although in the embryo they all arise according to the 

 same plan. We can think of the crayfish in its very early embryonic 

 condition as being somewhat like the clam worm with each segment 

 bearing a pair of appendages. The first four segments fuse to form the 



