Place the dish on the stage ofyourmicroscopesothatthe tail isunder
the low power objective. Observe.
Keep the fish tail wet byputtinga dropofaquariumwateron it every
fewminutes. Be sure to returnthe fish to his home in theaquarium imme-
diately after you have observed his tailunderthemicroscope. Be very gentle.
You will observe: The bloodflows in tiny tubes from the head region
towardthe tip of the tail and from the tip of the tail back towardthe head.
The fish has atube-likeheartin its"throat"(just behindthe gills)that
pumpsbloodtovariouspartsofthe body in tubescaJJedbloodvessels. The
large bloodvesselsthatcarrybloodawayfrom theheartare calledarteries.
The smaller blood vesselsthatcarrybloodback totheheartare called veins.
Still smaller bloodvesselsthatbranchall over the body arecaJJedcapillaries.
Blood brings food and oxygen to all the cells of the body and carries away
fromthes~cells many wasteproducts.THE ELEMENTS OF A"BALANCED" AQUARIUM
Materials:Threelarge test tubes withrubberstoppers,adhesive tape, two
small common snails (Physa), two smaJJwaterplants(elodea or cabomba),
a large-mouthedpintjar.
Follow thisprocedure:Fill thejarwithtapwaterand let itstandopenand
undisturbedforabout 48 hours. (This iscaJJed"aging.")
Fill one test tubetwo-thirdsfuJJof the agedwaterandplace one snail in
it. Putthe rubberstopperin place and wrap adhesive tape aroundthetop
so as to makethe tube relatively airtight.
Fill the second test tube two-thirdsfull of the aged water. Place in it
one snailanda sprig of elodea orcabomba. Seal it as you did the first tube.
Fill thethirdtest tube two-thirdsfull of agedwaterand place in it only
one smaJJ sprig of awaterplant. Seal it as you did the others.2 3