ZOOLOGICAL SOCIETY BULLETIN. 



843 



TERRARIUM IN A ROUND AQUARIUM JAR. 



Suitable for small salamanders, frogs and some turtles, 



land snails, etc. 



Similarly the light factor offers but little diffi- 

 culty and food can easily be added in the neces- 

 sary quantities. 



The problem of aeration is more difficult. In 

 the natural pond, with its large surface ruffled 

 by the breeze, this takes care of itself, as a suf- 

 ficient amount of oxygen can be absorbed from 

 the air to supply all the animals that can find 

 food within its waters ; but in the narrow limits 

 of the aquarium, with its restricted surface, 

 comparatively greater depth, and the absence of 

 any agitation of the water, the absorption of 

 oxygen at the surface does not take place with 

 sufficient rapidity to sustain much animal life. 



To supplement the surface absorption of oxy- 

 gen, it is necessary to grow plants in the aquar- 

 ium. It is a well known fact that in manufac- 

 turing their own food from simple substances, 

 plants give off oxygen as a waste product. This 

 process takes place in the chlorophyll, or green 

 matter of the plant, and in the submerged plants 

 of the aquarium the oxygen passes off directly 

 by absorption into the water. The fishes are 

 thus supplied with oxygen given off by the 

 plants as waste substance. 



Having absorbed the oxygen, the fishes com- 

 bine it with the carbon of the food to obtain 

 energy, and, in the process of respiration, give 

 off t.) the water quantities of carbon dioxide or 

 carbonic acid gas as a waste substance. This 

 gas, composed of carbon and oxygen, is ab- 

 sorbed by the plants and the carbon used in the 



process of starch making, while the oxygen is 

 returned to the water again as a waste sub- 

 stance. Thus the animals and the plants of the 

 aquarium are mutually benefitted, each supply- 

 ing something that is required in the life pro- 

 cesses of the other. 



Plants, however, are able to manufacture 

 starch, and consequently absorb carbon dioxide 

 and release oxygen, only when they are exposed 

 to sunlight. It follows then that on dark days 

 the plants have less capacity for aeration than 

 on bright days, and that they yield more oxygen 

 in sunny windows than in dark corners. More- 

 over they can make starch and consume carbon 

 dioxide and yield oxygen, only during the day- 

 time. Further than this, they consume a small 

 amount of oxygen in their own respiration both 

 day and night, so that at times when they are 

 not engaged in starch making they tend to con- 

 sume a part of the oxygen of the aquarium, al- 

 though they use only a small portion of that 

 thrown off during the day. If the water of the 

 standing aquarium is supplied with an excess of 

 oxygen during the day, a considerable amount 

 of the oxygen will remain in solution in the 

 water and aid in proper aeration throughout the 

 night. 



It is evident then that an aquarium well 

 stocked with plants will support a larger quan- 



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> i r i ? 



COMMON SALT-WATER SHRIMP. 

 They live well in the small aquarium. 



