70 LABORATORY DIRECTIONS 



7. Why are not air bubbles constantly ejected while the 

 crawfish is in the water? 



8. Make a diagram of a side view of the carapace, and 

 show by arrows the general course of the water currents. Explain 

 your diagram. Briefly summarize the method of aerating the gills. 



9. Examine a demonstration specimen prepared to show 

 the "gill bailer" in action. The "bailer" is a part of the second 

 in axilla. 



10. Observe to what degree the eye stalks are movable. 

 What evidence can you give that the crawfish sees ? 



II. EXTERNAL CHARACTERS 



1. Observe that the body is readily divisible into two re- 

 gions. The large anterior region, which is covered on the dorsal 

 and lateral surfaces by a non-jointed shell called the carapace, is 

 the cephalothorax. The remaining series of movable segments 

 behind the cephalothorax is the abdomen. 



2. Note the cervical groove, a slight depression extending 

 from the ventral margin to the dorsal surface of the carapace. 

 This groove marks the boundary between head and thorax. 



3. Examine the lateral margin of the carapace. This marks 

 the ventral boundary of the gillchamber. On the dorsal surface 

 of the carapace the gill chambers and pericardial chamber are 

 separated by a pair of longitudinal grooves called the branchio- 

 pericardial grooves. The rostrum is the sharply pointed projec- 

 tion of the cephalothorax between the eyes. 



4. Examine the ventral surface of the cephalothorax. Is 

 there any evidence of segmentation? Notes required. 



5. Note the texture of the skin. Where is it hard and where 

 is it soft? What is the relation of the texture to movability? 

 Notes required. 



6. How many segments in the abdomen? How many have 

 appendages? These appendages are called the swimtnerets, 



