LABORATORY AQUARIUM. 3 211 
in very small quantity. The Spirogyra has completely disap- 
peared and the jar now contains, besides the prettiest Chro- 
ococcus I have seen, Oedogonium forming zoospores, Conferva 
with zoospores escaped, a very rare stage which I have never 
seen in the field. The plant is so common as to be a nuisance 
in spring, both in pools and in the laboratory. The small ves- 
sel has been systematically robbed of part of its contents for 
pickling and supplying other laboratories, and it still continues 
to develop new material of the old forms, and shows indica- 
tions of producing new plants. This vessel is a round heavy 
glass box of the Bausch and Lomb make, and not more than 
four inches high and in diameter inside. 
ome plants prefer shallow wide vessels, other grow best 
in deep vessels. I find that most prefer shallow ones, and 
wide: those of five litres or less most convenient. They never 
bladders. They are then removed, as algae do not thrive with 
these higher plants present. Larger aquaria are especially 
good for growing small animals, such as entomostraca, snails, 
Fragania, Tubifex, planarians, Fairy-shrimps and hosts of 
others which live together harmoniously, or succeed one an- 
other. I have found that a larva stage of a dragon fly makes 
the best policeman for plant aquarium. When turned loose 
for a day or two destructive animals rapidly disappear. The 
larva lives long. I have had one do service for over a year. 
If left continuously in the plant jar its clumsy movements in- 
terfere with plant growth. There is no animal so destructive 
as the water snail. No plant culture will succeed when these 
are present and there seems no remedy, but to start withou 
hem. must be picked out by hand one by one. Most o 
the animals mentioned, though valuable to the teacher of zool- 
ogy for demonstration, are an intolerable nuisance in the 
aquarium. Animals should always be kept in separate jars 
