204 THE AMERICAN NATURALIST. [Vor. XXXIV. 
First a stencil of paper or pasteboard was used, but as this 
was not permanent enough, one of my students, living next 
door to a tinsmith, cut out the monogram of our school and 
attached it to the outside of the aquarium, having previously 
cleaned the inside with a scraper. In a few weeks the letters 
« D. H. S." were sharply marked by the sun's ray-pencils and 
the microscopic green plants within. (See figure in /ourn. 
Applied Micros., July, 1899, Vol. II, No. 7.) The stencil may 
be removed at any time for inspection, but should be kept in 
position the half of each day, while the strongest light falls on 
the aquarium to keep the letters from being obliterated. This 
experiment serves to illustrate the movement of green plants 
towards the source of light, and has interested many of our 
visitors. 
Such balanced aquaria also have a practical value in the 
schoolroom or laboratory; each one will have its own fauna, 
and may serve as a source of animalculee — Amcebz and other 
Protozoa so highly prized by the young teacher — and larger 
animals and plants for demonstration, experiment or research, 
in more nearly their natural environment, than those kept in 
water changed daily. This last spring we had a nice illustra- 
tion of this fact ; some fairy shrimps (Branchipus) were placed 
in a glass jar with water and plants of their habitat, and a few 
were placed in one of the balanced aquaria of the same size and 
receiving the same lighting. Those in the first jar died in a 
few days (the common experience of every one who has tried to 
keep them in the laboratory for demonstration), while those in 
the aquarium lived three times longer. 
In one small aquarium jar, set up over a year ago, containing 
mostly diatoms, Oscillaria, some water fleas and Rotatoria, there 
has been a good supply of Amcebz for class use. Another 
larger one, képt over two and one half years, in which a large 
` snail, some water weed, and smaller animals constitute the 
balance, furnishes sun animalcules for demonstration. The 
largest one, with glass plate sides, slate bottom and ends, has 
been kept nearly two years without change or addition of water. 
It is stocked with aquatic plants, Cladophora, Myriophyllum, 
Lemna, Wolffia, Anacharis, and many single-celled algae. The 
