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V^II. — Convection-Current Circulation in Laboratory Aquaria r 

 an Aid to the Hearing of Pelagic Larvae. 



By James F. Gemmill, M.A. M.D., D.Sc. 



Lecturer in Embryology, Glasgow University, and in 

 Zoolos^v, Glasgow Provincial Traininsj College. 



[Read February 19, 1913.) 

 Plate XI. 



The following arrangement provides a simple and effective method 

 of ensuring gentle circulation and aeration, as well as cooling, either 

 in a single small . laboratory aquarium, or in a series of such 

 aquaria. It can be applied wherever the temperature of the 

 ordinary tap water is some degrees lower than that of the interior 

 of the laboratory, a condition which practically always exists. 



What follows will be made clear by a reference to Plate XL 

 Cool tap water circulates through one or more U tubes of glass and 

 then either runs to waste, or can be employed, if necessary, to work 

 a low pressure intermittent aerating apparatus.* The U tubes dip 

 down from above for some distance into the middle of the aquaria, 

 and cool the water in immediate contact with their surfaces. A 

 downward convection-current from top to bottom is thereby caused 

 in the middle of each aquarium. A compensating upward con- 

 vection-current occurs everywhere in the layer of water close to 

 the aquarium wall, this wall being exposed to the higher temper- 

 ature of the laboratory. So much surface water is carried down in 

 the descending stream, that adequate oxygenation of the whole- 

 volume is ensured. 



For the most part I employed, as aquaria, tall beakers of flint- 

 glass, holding rather more than half a gallon when filled up to 

 about 9 in. from the bottom. These make very good convection- 

 current aquaria, since the thin glass readily conducts heat from 

 the outside to the contained water. The U tubes were of ordinary 

 glass tubing J in. in external diameter, and they dipped down 

 4^ in. into the water, leaving the same distance between their 

 lower ends and the bottom of the vessels. So far, I have only been 

 working with salt water aquaria, but the same results should be 

 produced in fresh water as well. 



* See this Journal, 1910, p. 11. 



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