ANIMALS OF POND AND STREAM 31 



Can you detect his method of breathing ? Look at the prepared museum 

 specimens showing the gills. Probably some of the specimens collected 

 will bear eggs. Where are these attached ? Look up the life-history and 

 see if the eggs develop into nymphs or larvae. 



Plankton. Compare the water sow bug and the bender with the cray- 

 fish. In some of the material that has been brought back from the pond 

 and allowed to stand in the jars you will probably see some very much 

 smaller relatives of the crayfish. Learn to recognize the Daphnia, Cyclops, 

 and Cypris. These crustaceans, while apparently insignificant, are of 

 large economic importance. Find out their use. Find out how abundant 

 they are in lake or river water, and also how rapidly they reproduce. The 

 sum total of small plants and animals floating or swimming in the water is 

 known as the plankton. Find out from books how much there is of it in 

 ordinary lake or river water. 



Study of the dragon-fly nymph. In the material dredged up from the 

 pond the nymphs of the dragon fly and the damsel fly will undoubtedly be 

 found. These as well as other insect larvae may be determined by the 

 accompanying key. In our insect study we have observed dragon flies 

 laying their eggs. The eggs hatch into the tiny nymphs. Have you the 

 nymphs of more than one kind of dragon fly ? Lift one of the good-sized 

 nymphs from the water and observe the construction of the accessory 

 jaws borne on the arm that hinges below the mouth. You can gently take 

 hold of this pair of accessory jaws and extend the arm. How would they 

 serve in capturing prey ? Keep some of the largest of the dragon-fly nymphs 

 in a jar by themselves, supplying them freely with smaller insect larvae for 

 food. Put a stick in the jar so that it will project above the water and cover 

 the jar with a piece of cloth. Probably some of the nymphs will mount the 

 stick and transform into the adult dragon fly. The process is well worth 

 watching. Look on the grasses and rushes along the margin of the pond 

 for such cast-off skins. 



The mosquito's life-history. You will probably find mosquito larvae 

 or pupae in the water brought back from the pond. If not, make a special 

 trip for them. The larvae are the wrigglers often found in a rain barrel or 

 other stagnant water. Put several of them into a tumbler of water and 

 watch their movements. When undisturbed where do they rest? Are 

 they lighter or heavier than water? Is it an effort for them to go down 

 under the water? How do they accomplish this? Do they have jaws? 

 Learn to recognize the pupa. What is its position at rest ? Make a sketch 

 of the larva and of the pupa. Cover the tumbler in which there are a 

 number of pupae and watch for the transformation of the pupa into the 

 adult mosquito. Where does the adult stand while it is drying its wings ? 



