Marine Aquaria 



21 



Water used in the experiments on fertilization of eggs, development 

 of larvae, etc., should never be taken directly from the laboratory faucet. 

 A suitable container, such as a one or two liter flask, should be filled and 

 set aside for several hours before using to permit the escape of excess 

 of air. For metabolic studies all the micro-organisms suspended in the 

 water must be carefully removed by filtration through a suitable filter 

 and the oxygen content of the sample must be standardized. 



Agitation. Agitation of water is essential for maintaining certain 



forms such as jelly fishes, small crustaceans, larvae of lamellibranch 



1 1 



1 1 



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Fig. 25.— The plunger jar. After E. T. Browne. A, glass disc or plate; B, glass 

 rod; C, lever; D, axis of lever; E, bar to stop downward motion of bucket; F, bucket; 

 H, flexible hose; K, string; S, siphon. 



mollusks, etc., which otherwise settle on the bottom, stick to each other, 

 and die. In the aquaria with running seawater the inlets and outlets may 

 be arranged so as to provide efficient circulation. When the water is 

 not changed for several days or weeks, some method of mechanical agi- 

 tation is necessary. In a small aquarium this may be accomplished by 

 blowing air through glass tubing lowered to the bottom of the tank. 

 Should aeration not be desired, various kinds of stirring apparatus may 

 be used. There are on the market many types of stirrers, consisting of 

 glass or metal propellers rotated by means of electric motors, which may 

 be adapted to this purpose. The difficulties are that in most cases the 

 stirring devices are designed for use during a limited period of time and 

 are not suitable for long, continuous use. A very simple and practical 

 device which overcomes this difficulty was designed by Browne (1907) 

 and is known as a plunger jar (Fig. 25). It consists of a glass disk or 

 plate (A) suspended from one end of the lever (C), rotating along axis 



