CHAPTER XI 



ANIMAL STUDY: THE AQUARIUM; THE INSECT CAGE; 

 OTHER ANIMALS 



At least two lines of animal study will commend them- 

 selves to the teacher because of the relatively large returns 

 obtained from a small expenditure of time. These are the 

 study of life by means of the aquarium and of the insect 

 cage. The uses of the aquarium in nature study are so 



many and so important that it may be con- 

 The 



Aquarium sidered almost a necessity. To be success- 



ful with the aquarium, we must imitate 

 somewhat closely the conditions that exist in open ponds, 

 for these are natural aquaria. During the warmer season 

 such ponds teem with animal and vegetable life. Ponds 

 present a great amount of surface to the air; in a sense, 

 they breathe. That is, they are constantly giving off car- 

 bon dioxide, and receiving oxygen by diffusion. In ponds 

 containing a large amount of plant life this exchange is 

 largely between the water and the plants. Our aquarium 

 presents relatively less surface to the air, so it must? contain 

 a greater amount of aquatic plant life, such as normally 

 produces its green tissues under water. Some plants of 

 this nature are the different varieties of swamp grasses, 

 water-crowfoot, water milfoil, and the" fresh water algae. 

 Plants which produce their green parts above the surface 

 of the water and those which float upon it do not supply 

 oxygen to the aquarium, although they may add to its 

 beauty or may serve other important purposes. 



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