136 AQUARIA. FOR MICROSCOPIC LIFE. 



about how much plant-Hfe there should be in a given quantity of 

 water, and where the aquarium should be placed to ensure the 

 most satisfactory growth. 



It need not be said that the conditions of prolific growth in an 

 aquarium are the same as are found in open ponds ; but to imitate 

 those conditions indoors requires some judgment. The collector 

 will observe that the water in ponds, although freely exposed to 

 the glare of the sun, never becomes greatly heated, because of the 

 rapid evaporation from the surface. But if an ordinary aquarium 

 be thus exposed to the sun, the small body of water would soon 

 become so warm that many organisms would die in it. Therefore, 

 the aquarium should not be placed in sunlight. By far the best 

 place is near a window where it can receive good light from the 

 sky all day long, but no direct sunlight. The first, and most im- 

 portant rule is, to keep the water cool. 



For microscopic specimens, a small bottle, holding about 6 

 ounces, with square sides, makes an excellent aquarium. Such 

 bottles should be about two-thirds filled with water, and covered to 

 exclude dust. We have used the tin-foil that tobacco is wrapped 

 in to cover them, and found it well adapted to the purpose. 

 Several of these bottles should be kept with sprigs of water-plants 

 growing in them, so that whenever an interesting specimen is found 

 it can be put into one of them, to grow and multiply by itself. In 

 this way, it is sometimes possible to cultivate microscopic forms of 

 life very successfully. We have thus grown hundreds of the 

 common rotifers, and kept them for weeks in the winter-time. 

 That was done, however, in a one-ounce bottle, which had a small 

 bit of Nitella in it. We have also kept Volvox in fine condition 

 for many days in a small bottle covered with a watch-glass. 



Beginners in this work are apt to put too much material into 

 their jars. A very small bit of a vigorously-growing plant will 

 suffice, and if too much is introduced, it will soon lose its vigour, 

 and some of it will decay and make the water impure. 



The jars should not be disturbed much, and when they are 

 moved they should be handled carefully, and then replaced as they 

 were before, in order to ensure uniform conditions of light and 

 temperature. 



We have seldom been troubled with an excessive growth of 

 unicellular alg?e on the sides of our jars. Usually these come 

 from an excess of light. But a filamentous Cladophora found its 

 way into one of our larger jars more than a year ago, and it became 

 such a nuisance that finally the jar was given over to that plant 

 entirely, and is now green with it. When the jar is wanted for 

 other use, it must be washed in boiling water to get rid of the too- 

 prolific alga. When minute algae do come in such abundance as 



