2 THE CANADIAN NATURALIST. [Mai'ch 



or stream. Nothing mars the effect more than to see marine 

 shells, gay corals, madrepores, and echinoderms, however 

 beautiful and interesting in themselves, in a fresh water aqua- 

 rium. Even gold-fish are out of place among our Canadian fishes 

 there, and detract from the truthfulness of the representation of 

 a local fauna. Our waters contain the beauties of the Creator's 

 hand just as much as those of a foreign shore, and the object of 

 all lovers of aquaria should be to correctly illustrate the habits 

 of native species. 



The bottom of the tank ought to resemble the bed of a pond 

 or river, with pieces of rock-work here and there, having their 

 tops standing out of the water, to allow those creatures which 

 prefer out-door exercise to breathe the fresh air at pleasure. 



The principles on which an aquarium should be constructed 

 are the following. The vessel should be either oblong or square, 

 but not globe-shaped, on account of its distorting the image of 

 whatever is contained in it. This should contain animal and 

 vegetable life, in fresh or salt water, which, like the water of a 

 river or sea, need never be changed. The vitalization of the 

 water, without its being changed, constitutes the main principle 

 of the aquarium ; this principle we shall now endeavour to 

 explain. 



Living animals absorb oxygen, and give off carbonic acid gas. 

 Plants, on the contrary, exhale oxygen, and inhale carbonic acid. 

 What the one accepts the other rejects ; that which would suffocate 

 the one if it was not removed, the other would die from exhaus- 

 tion if it couH not obtain. 



In stocking an aquarium, judgment and discretion are required, 

 so as to have an equal proportion of animal and vegetable life. 

 It should also be remembered that the more rock you introduce 

 the fewer fish must be put in. A little experience in the keeping 

 of aquaria will soon make people aware of any disproportion in 

 the balance of animal and vegetable life. If plants are in excess, 

 this is shown by the particular clearness of the water and by the 

 restlessness of the fish. Their motions are spasmodic ; they swim 

 backwards and forwards in darts and jerks, as if trying to escape 

 from something. If, on the other hand, there is too little vegeta- 

 tion, the fish swim lazily, with their mouths out of the water, 

 panting for oxygen. 



Our aquarium is three feet six inches long, by two wide, and 

 twenty inches in depth. It has a glass top or roof-shaped 



