36 ETON NATURE-STUDY 



Seeing that most forms of animal life are far more abundant 

 in salt than fresh water, we must assume that the rarity of marine 

 aquaria is due either to the greater difficulties that attend their 

 successful management, or perhaps to the belief that water from the 

 sea can alone be used. 



In many large aquaria the salt water is artificial, notably in the 

 splendidly arranged tanks in Berlin, belonging to one of the finest 

 aquaria in the world. The proper kind of salt is easy to get, and 

 all that has to be done is to dissolve it in distilled water until the 

 right specific gravity is obtained. Full directions as to how this may 

 be done are supplied by the makers of the salt which is sold by all 

 chemists (see appendix page 149). 



As to the special difficulties which beset the keeping of a marine 

 aquarium, the proper aeration of the water is doubtless the greatest. 

 As a rule marine plants will not grow readily, but die after a few 

 weeks. Various methods are given in the handbooks which deal 

 with the keeping of aquaria, but perhaps the best and, after all, the 

 simplest way, is to syringe the water for ten minutes at least once 

 a day, taking care that the water carries down plenty of air bubbles 

 at each stroke of the piston. Some naturalists are able with care to 

 maintain their aquaria practically untouched for years at a time.* 



The dangers of overcrowding are also great, and unless the utmost 

 care is taken in this respect, the results will be disastrous. As a 

 rule, indeed, unless the greatest caution is exercised, the inhabitants 

 of salt water aquaria, kept at a distance from the sea, will after a few 

 weeks be found to consist almost entirely of anemones, everything 

 else having perished. 



It will perhaps be thought that as the difficulties of keeping an 



* See " Notes " by Mr Sibert Saunders in the official report of the Nature Study Ex- 

 hibition, 1902 (Blackie 1903) and "Marine Aquaria" by R. A. K. Bennett, B.A., Upcott 

 Gill (price 2s. 6d.). 



