THE CRAYFISH 43 



fish ever come out of their burrows ? Is the inside of the 

 burrow smooth or rough? How high is the chimney and 

 how is it constructed? Does this crayfish ever do any 

 harm ? On what does it live ? 



Catch a live specimen and put it in an aquarium. Note 

 its manner of movement. How many legs does it use in 

 locomotion? Poke a stick or straw at its head. Which 

 way and how does it move? How is the abdomen held? 

 Note the eyes of the animal. Note its feeding habits. What 

 does it eat ? How does it catch its prey ? 



B. EXTERNAL FEATURES. Note that the body of the 

 crayfish is divided into two principal regions. The anterior 

 region consists of the head and thorax joined together and 

 appears as one piece. This is called the cephalothorax. The 

 posterior division is the abdomen. Note that the abdomen 

 is plainly segmented. Does this aid in the movements of 

 the animal? Note that the whole body is encased in a 

 hard covering, or crust. This crust is hardened by a de- 

 position of lime carbonate. As the crayfish grows, this crust, 

 or hardened skin, is shed from time to time. 



Make a drawing of the crayfish from above. 



Note that the cephalothorax, when viewed from above, 

 shows no signs of being segmented. Look on the ventral 

 surface, however, and the division into segments may be 

 seen. Note that the top of the cephalothorax is covered 

 with a single large piece called the carapace. The division 

 between the head and thorax is marked by a shallow 

 groove that runs transversely across the carapace, and 

 then continues forward in an oblique direction on each 

 side. Note that the carapace in front extends forward be- 

 tween the eyes, forming a concave pointed beak. This is 

 known as the rostrum. 



