REVIEW QUESTIONS. 75 



and lobstei" are very nearly alike. A crab differs from 

 a crawfish in the fact that the abdomen is very much 

 reduced in size and is folded under the cephalothorax. 



The sow bug belongs to an order called Tetrade- 

 capoda, or fourteen-footed crustaceans. The gills are 

 leaf-like plates' situated under the abdomen. The 

 animal lives in damp places, although most members 

 of the order are truly water animals. 



Daphnia, Cyclops, and Cypris belong to the order 

 Entromostraca. They are all very small crustaceans, 

 are found abundantly in our lakes and ponds, and 

 furnish a part of the food for young fishes. The order 

 is now divided into three groups, called Copepoda, 

 Cladocera, and Ostracoda, represented by Cyclops, 

 Daphnia, and Cypris, respectively. 



Review Questions. 



The Crawfish. 



1. What are the body divisions of the crawfish? 



2. What is the cervical groove? 



3. Where is the rostrum? 



4. Where is the telson? 



5. How many segments in the abdomen? 



6. What is the carapace? 



7. Name all the appendages of the crawfish? 



8. Are the eyes stalked or sessile? 



9. What appendages bear gills? 



10. How many gills does each of the gill-bearing ap- 



pendages have? 



11. What is the gill scoop? What is its use? 



12. To what is the gill scoop attached? 



13. Describe the function of the gills. 



14. How is a current of Avater produced over the gills? 



What makes it flow? Describe its course. 



15. What is the typical form of an appendage? Name 



the three principal parts. 



