156 ANIMAL BIOLOGY 



2. Of what use may the mouth parts (easily seen in a living 



cra3rfish) be in getting food into the mouth ? 



3. Push the outer mouth parts of a Uving crayfish to one side 



with the forceps and find a pair of hard jaws, 

 mandibles. Pry them open a little. 



a. Do they work from side to side or up and down? 



6. Describe the cutting edges of the mandibles. 



c. Of what use would these jaws be in preparing food for 

 swallowing? 



F. (Optional.) Adaptations for protection. 



1. Describe the outer covering of the animal ? Of what use is 



this to the animal ? 



2. Locate the softer parts of the crayfish's armor? How are 



these protected by their position ? 



3. Gently touch the eye of a Uving crayfish. 



a. Describe the movements of the eye. How might these 

 movements be advantageous to the animal? 



6. Of what advantage may it be to the crayfish to have its 

 eyes on stalks instead of on the surface of the head ? 



c. Make a sketch (X 4) of one of the eyes on its stalk. 

 Label : fleshy stalk, eye. 



4. Of what use may the large pincers be in addition to helping 



in securing food? Sketch (XI) one of the large 

 pincers complete. 



G. (Optional.) Additional drawings. 



1. Make out the parts of one of the large antennae. Notice 



the broad finlike part at the base of the antenna, 

 then two segments, and a long lash that arises from 

 the second segment. Sketch (X2) a large anteima. 

 Label. 



2. Make a sketch (x 1) of dorsal view of the crayfish. Label 



the regions, and all the appendages. 



113. Habits of crayfishes. — Crayfish are found commonly 

 throughout the United States in rivers and their tributaries 



