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or come to the surface for their supply. How does Mother Nature 

 manage the ventilation of her aquaria, the ponds and streams ? The 

 plants furnish part of the air, as we have seen. The open pond, 

 whose surface is ruffled by every passing breeze, is constantly being 

 provided with fresh air. A tadpole or a fish can no more live in a 

 long-necked bottle than a boy can live in a chimney. 



3. The temperature should be kept between 40° and 50^ 

 Fahr. Both nature and experience teach us this. A shady cor- 

 ner is a better place for the aquarium than a sunny window on a 

 warm day. 



4. It is well to choose such animals for the aquarium as are 

 adapted to life in still water. Unless one has an arrangement of 

 water pipes to supply a constant flow of water through the 

 aquarium it is best not to try to keep creatures that we find in swift 

 streams. 



Practical experience shows that there are certain dangers to 

 guard against — dangers which may result in the unnecessary suffering 

 of the innocent. Perhaps the most serious results come from 

 overstocking. It is better to have too few plants or animals than 

 too many of either. A great deal of light, especially bright 

 sunlight, is not good for the aquarium. A pond that is not shaded 

 soon becomes green with a thick growth of slime, or algae. This 

 does not look well in an aquarium and is apt to take up so 

 much of the plant food that the other plants are '' starved out." 

 The plants in the schoolroom window will shade the aquarium 

 nicely, just as the trees and shrubs on its banks shade the pond. 

 If we find this slime forming on the light side of our miniature 

 pond we put it in a darker place, shade it heavily so that the 

 light comes in from the top only, and put in a few more snails. 

 These will make quick work of the green slime, for they are fond of 

 it, if we are not. 



Some of the most innocent of our " water nymphs " are reall) 

 concealing habits which we can hardly approve. There arc 

 some which feed on their smaller and weaker neighbors, and 

 even on the members of their own families. We know that 

 such things go on in nature, but if we wish to have a happy 

 family we may improve on nature and keep the cannibals by them- 

 selves. 



