ZOOLOGICAL SOCIETY BULLETIN. 



841 



SEA-LETTUCE (Ulva). 



It is the best aerator. The red-seaweeds add color and variety 



and should be placed at the bottom of the tank. 



sons who for years had kept aquaria equipped 

 with plants and animals for proper balance, 

 who still thought it necessary to change daily all 

 or part of the water in order to maintain the 

 animal life. 



The writer well recalls his own early attempts 

 as a child to keep small native fishes in an 

 aquarium made of a cast-off wash-boiler par- 

 tially sunk in the ground in the garden, and the 

 ingenuity with which he rigged a small tube to 

 the pump-spout by the horse trough so that 

 when anj-one pumped water a small portion 

 would escape for the benefit of the fishes. A 

 few water weeds would have done the work of 

 aeration more successfully and with much less 

 trouble ; but the knowledge of the proper method 

 was lacking, and after a number of abortive at- 

 tempts the experiment was given up in despair. 

 I have no doubt that thousands of persons have 

 had similar experiences with various kinds of 

 fish globes and other improper aquarium a])- 

 paratus. 



Another prevailing notion is, that the small 

 aquarium is simply a plaything serving to 

 amuse the children or to afford an outlet for the 

 energies of an occasional crank; and its onlv 

 other excuse for existence is found in the fact 

 that the green plants and goldfishes make a 

 bright spot in the room. Even if this were all, 

 wlio will deny that its existence is justified.^ 

 But excuses are not necessary. Let it serve for 

 the one as a plaything or bright spot in the 

 room, but for the person who cares to study the 

 life in the aquarium — and there is a constantly 

 increasing number — the aquarium becomes a 



piece of scientific apparatus from which can be 

 learned many of Nature's laws that regulate the 

 outside world. 



The unbalanced fish globe with its occasional 

 renewal of water is unnatural, — as unnatural as 

 the attempt of a person to live in a closet by 

 opening the door once a day, filling the space 

 with fresh air, then shutting off all ventilation 

 until the next day. The cases, as far as respira- 

 tion is concerned, are exactly parallel. It is 

 possible to supply oxygen to fishes in the small 

 aquarium by means of apparatus which will 

 pump the air into the water, but this again only 

 meets the problem half way. It supplies the 

 oxygen, but does not remove the carbon dioxide 

 which can escape only by passing into the air at 

 the surface of the water. 



The balance of plant and animal life means 

 complete and continual ventilation. Not only 

 is oxygen supplied in sufficient quantities by the 

 plants, but the carbon dioxide given off bj' the 

 animals in respiration is consumed by the plants 

 in the process of starch making. The adjust- 

 ment is Nature's own and all animals are adapt- 

 ed to it. Such an arrangement is a pond in min- 

 iature and may be used in the scientific study of 

 aquatic life of various kinds. In the majority 

 of cases, to be sure, only goldfishes are kept, in 

 addition to a tadpole or a few snails and plants. 



According to the interests of tlie aquarist, 

 however, this may be varied indefinitely. Vari- 

 ous other attractive exotic fishes of striking 

 colors, form and habits may be readily secured 

 from dealers, or the collector may take up the 



GOURAMI [Osphronu-niis olfnx). 

 exotic specimen lived for several years at the 



