16 THE AQUAVIVARIUM. 



practice of keeping the windows of our dwellings 

 closed winter and summer. Fortunately, no evil 

 arises from sealing up our Aquavivarium, and we 

 may cover it in with what material we please. 

 Mr. Warington originally strained a piece of muslin 

 over his jar to keep out the " blacks : " we have 

 always used a piece of glass. The glass has this 

 advantage, that whilst it stops the access of the 

 blacks, it prevents evaporation, and allows also the 

 top of the Aquavivarium to be used for placing 

 objects which serve for ornament and adornment. 

 Covers made of opaque objects are not desirable, as 

 they prevent the access of light, and thus interfere 

 with the growth of the plants and obscure the 

 view of the objects. Arrangements are often made 

 for allowing the access of air between the cover and 

 the vessel, but this does not appear to be necessary, 

 although there can be little doubt that injury would 

 occur were the vessels hermetically sealed. 



The form of the tank will be found very conve- 

 nient for making other arrangements. We have 

 seen how an Aquavivarium may be introduced 

 into a Ward's case ; and by enlarging a tank, and 

 covering it over close, we may convert an Aqua- 

 vivarium into a Ward's case. If rocks are intro- 

 duced into the middle, our Aquavivarium may 

 be converted into a miniature lake with an island 

 in it. On the rock may be grown ferns of various 

 kinds, or other plants which love the rocks that 

 are dashed by the spray of water. Such an Aqua- 

 vivarium should be made of large size ; and where 

 a running stream can be introduced through it, 

 such large fish as pike, trout, and tench may be 

 kept. 



It will be observed from the last remark, that 

 there are limits within which plants and animals 

 will grow and live in our tanks ; the weight of 



