THE AQUARIUM 



BY MARION I. NEWBIGIN, D.Sc., 



Lecturer on Zoology, Edinburgh School of Medicine for Women ; 

 Author of " Life by the Seashore," etc. 



CHAPTER X 



The Principle of the Aquarium. As a considerable number of 

 the plants and animals which the teacher is likely to use for the 

 giving of lessons are aquatic in habit, and as many can only be 

 obtained on special excursions, the idea of keeping some of these 

 in captivity readily presents itself. In this way not only are 

 the specimens at hand when required, but also their habits can 

 be studied in an amount of detail which is impossible in a state 

 of nature. It should, however, be noted that an aquarium in 

 the strict sense means something more than this. In 'theory 

 at least it means the keeping together of plants and animals in 

 such a way as to demonstrate their interdependence in nature. 

 It was the proof of this interdependence which gave such an 

 extraordinary impetus to aquarium-keeping some sixty years 

 ago, and it is in itself so striking a generalisation that no course 

 of nature study would be complete without some mention of it. 



Some very simple preliminary experiments may prepare the 

 way for its complete formulation. Take a handful of green 

 seaweed from a shore pool, or some water-weed from a pond, and 

 put it in a glass vessel with water, salt or fresh according to the 

 plant, in the sunlight in a warm room. In a very short time 

 small bubbles form over the surface of the weed, and these then 

 coalesce, thus becoming larger, and rise through the water to 

 escape at its surface. If, for example, a piece of green laver 

 (Ulva latissima) be taken from a pool and tested in this way, 

 the gas as it comes off will buoy up the weed, which then floats 

 in the water near the surface, the rapid discharge of bubbles giving 



