:«) NINETEENTH HEl^ORT. 



tlirough the glass^ yet this is not marked enougli to exclude them from 

 use. The size must of course depend to some extent upon the storing 

 place for the tank and the number and size of the animals which it must 

 contain. In general, much more pleasure as well as instruction can be 

 derived from several small aquaria than from one large one, not only 

 because the small tanks are more easily cared for, but also because of 

 the greater variety of animal life thus afforded for observation and 

 study. Animals must be more or less segregated according to their size 

 and habits. The number of sjiecies possible in a single aquarium is not 

 necessarily great. 



The balanced aquarium, strictly speaking, is just what the name im- 

 plies, that is, an aquarium in which the plant and animal life is so 

 balanced that aeration of the water takes place automatically and the 

 food cycle is comj^lete. In the ordinary small aquarium, however, it 

 will be found advisable to modify the balance by the introduction of food 

 for some of the larger animals. The plant and animal life is mutually 

 beneficial and artificial aeration such as running water or compressed 

 air is unnecessary. Thoroughly washed sand should be placed on the 

 Hoor to the depth of an inch at least, and on toj) of this a layer of fine 

 and medium sized gravel, also thoroughly washed, of approximately the 

 same depth. The depth of the sand and gravel is important since they 

 form the rooting place for the plant life, and there is frequently a greater 

 tendency to use too little rather than too much. Both sand and gravel, 

 if not easily obtained elsewhere, can usually be found where cement 

 work is being done or has bc-ii done recently. 



Water jilants suitable for an aquarium can usually be foiuid until late 

 in the fall in almost any small river, creek, ditch, small lake or permanent 

 pond. They maj' also be purchased from dealers carrying goldfish and 

 aquarium or fish supplies. The more common plants* for the region 

 about Ann Arbor, Michigan, are — 



Hornwort ( CeratopJii/llum demersum). Eggeling and Ehrenberg, pp. 

 35 and 40. 



Crystal worts ( liiccia fl nitons and R. natans). Bateman and Bennett, 

 J)}). 90-1, Eggeling and Ehrenberg, p. 91. 



Canadian waterweed ( FAodea canadensis). Eggeling and Ehrenberg, 

 pp. 43- 1-. 



Small duckweed (Lrmna minor). Bateman and Bennett, p. Sh, 

 Eggeling and Ehrenberg, p. 86. 



Three-leaved duckweed ( Lemna tri.snlca). Bateman and Bennet, p. 

 89, Eggeling and Ehrenberg, p. 87. 



Water milfoil or ThousaJid-leaf (Mifriupliifllnni lulcropltifUum ). 

 Eggeling and Ehrenberg, p. 70. 



*The writer is inclehted to Hr. .1. M. I'(illii<k fur ,issist.ui<i> in prepariii}; the list of pl:»iits. 



