32 A FIELD GUIDE IN NATURE-STUDY 



Put a couple of minnows or other small fish into the aquarium where 

 there are mosquito larvae and pupae. What happens ? Put a number of 

 larvae into each of two tumblers two-thirds full of water. Drop a drop of 

 kerosene oil on the surface of the water of one of these tumblers. What 

 happens ? What practical application is made of this ? 



Movements of animals of pond and stream. How does the dragon-fly 

 nymph usually move ? Poke at it with your pencil and see in what other 

 way it moves. You may have to read to some extent to understand how 

 it accomplishes this. Is the diving beetle, Dytiscus, heavier than water or 

 lighter ? How does it swim ? Is its shape one that would fit it for move- 

 ment through water? How are the legs adapted to swimming? Watch 

 the swimming of the giant water bug, the back swimmer, the water boat- 

 man. How do they swim and how are they structurally adapted to so 

 moving ? Draw some one of them and make an enlarged sketch of the leg 

 to show the adaptations. Watch the water spider or the water strider as it 

 runs on the water. Sketch the shadow of the water strider seen on the 

 bottom of pond or aquarium. How does the strider accomplish the miracle 

 of walking on the water? Blow a soap bubble with a pipe and let the 

 bottom of it rest on the surface of the soapy water, then lift the pipe. Is 

 the bubble drawn out of shape ? This shows what ? Hold a fine needle 

 between thumb and finger a very short distance above the water in a full 

 tumbler, the needle parallel to the surface of the water. Let it drop to the 

 surface. If the experiment is done carefully the needle will remain on the 

 surface. Look up the experiment with the Mensbrugge float and try it. 



Is the goldfish heavier than water, lighter, or of the same specific 

 gravity ? Are you heavier than water or lighter than water ? Why then 

 does one drown ? Does a fish have anything in its body that helps to keep 

 it afloat ? 



If you were to cut through the fish's body from snout to tail what would 

 be the outline of the surface exposed? Draw it. Draw the outline to 

 represent the line on which the hull of a boat cuts the surface of the water. 

 What is the shape of a submarine? How many fins has the goldfish (or 

 the chub) ? Where are they located ? How are they used ? What fins 

 does the fish use chiefly in swimming ? How does it turn around ? How 

 does it turn toward the surface? Watch the turtle in the water. What 

 methods of locomotion has it ? How does it swim ? Watch a snail ' ' crawl. ' ' 

 How does it do it ? Can it crawl on the surface of the water ? Can it swim ? 



Breathing. What is the position of the diving beetle when at rest? 

 of the back swimmer? Take Dytiscus out of the water; lift up the elytra 

 or horny wing covers. Note the membranous underwings, the ones he 

 really uses in flight. What else is between the elytra and the abdomen ? 



