174 ARTHROPOD A. 



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 

 pecuhar reaction to light. If the light is cut off from the micro- 

 scope, 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 antennoe are veiy small and project ventrally. 

 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 com- 

 posed of cheese-cloth or silk bolting-cloth, will yield an abun- 

 dance of material. 



1. Watch the animals and see how they swim. With a 

 pipet try to catch a certain individual and see whether the jerky 

 movements probably aid these animals in escaping enemies. 

 Determine what organs are used in swimming. 



2. Examine specimens that have been confined under a cover- 



