OTHER CRUSTACEANS 47 



this same branch ? To what class does it belong ? Name 

 the other animals belonging to the same class. Compare the 

 crayfish with a lobster. 



Sum up the chief characteristics of the crayfish. Fix 

 firmly in mind its position in the animal kingdom. Give 

 a summary of its habits, food, habitats, and economic im- 

 portance. Write out a comparison between it and the 

 locust. 



XV. OTHER CRUSTACEANS 



Materials. Specimens of cyclops, cypris, daphnia, crabs (Rock 

 and Hermit) ; watch glass. 



Directions. (Cyclops, cypris, and daphnia are small crus- 

 taceans that live in fresh-water ponds. They may be obtained in 

 abundance in jars of pond water containing Algae that have been 

 brought into the laboratory. Though small, they are visible to the 

 unaided eye.) 



A. CYCLOPS. Take some of these out in a watch crystal, 

 and observe, carefully, their movements. Is the progres- 

 sion a smooth, gradual one or a jerky one? Their mode 

 of motion has given them the name of " water fleas." 



Note the shape of the body, large at the anterior end and 

 tapering to the posterior end, convex above and flat below. 



Note the one dark eye at the anterior end of the body 

 on the dorsal side. Note the two long appendages at the 

 anterior end of the body, called the antennules. There is 

 also a pair of short antennae that are often hidden beneath 

 the head. Observe that there are five pairs of appendages 

 on the ventral side of the body. The body is segmented, 

 but note the large piece covering the anterior end of the 

 body. This is the carapace. The tip of the abdomen ends 



