186 ARTHROPODA 



DAPHNIA 



This small fresh-water form frequently occurs in large 

 numbers in small pools and brooks. Determine how it swims. 

 Being small and transparent, it may be satisfactorily studied 

 with a compound microscope. 



1. Notice the shape and extent of the protective covering. 

 To what part of other crustaceans does this correspond? Are 

 the appendages and the abdomen capable of being thrust 

 out? Are there any signs of segmentation of the body? 



2. Determine what parts are used in keeping a current of 

 water passing through the shell. Why is such a current 

 needed? 



3. If the animal carries young, notice how they are kept 

 in the brood chamber by a spine that extends up from the 

 dorsal portion of the base of the abdomen. 



4. Notice the beating of the heart. 



5. Are the eyes stalked or sessile? They frequently show 

 a peculiar reaction to light. If the light is cut off from the 

 microscope, the eye will be seen to rotate on its axis. If the 

 light is admitted again, the eye rotates back to its original 

 position. 



6. The first antennae are very small and project ven- 

 trally. What is the chief function of the second antennae? 



7. Several appendages will be seen inside of the shell, but 

 it is hard to determine their exact relation. The functions 

 of some of them may be apparent. 



A drawing is desirable. 



CYCLOPS (Water-flea) 



Almost any free-swimming copepod, either fresh water or 

 marine, will answer quite as well as the fresh-water Cyclops. 



Cyclops may be found in almost any pool of fresh water 

 and the marine forms are among the most abundant of the 

 animals of the sea. Surface skimming of the sea, made with 

 a net composed of cheese cloth or silk bolting cloth, will 

 yield an abundance of material. 



