12 THE MICROSCOPICAL NEWS. 
exceptionally favourable opportunities afforded by large tanks 
supplied with thoroughly aerated, constantly running water, which 
can only be found in aquaria established for purposes of exhibition. 
At the celebrated Brighton aquarium, which is one of the most 
successful in England, for it has paid well, another disputed 
question has been settled in an interesting manner. It was sup- 
posed by some naturalists and fishermen that the ova of the cod 
and the whiting were deposited on the sea-bottom, and if so it was 
feared that trawling would destroy the spawn, and thereby diminish 
the product of the fisheries. Experiment proved, however, that the 
eggs of both those fish would not sink, but floated on the surface 
of the water. At the same aquarium the rapidity of the growth of 
the salmon has been studied. Not to weary the reader with other 
facts of this kind, probably enough has been said to indicate the - 
utility of large aquaria for purposes of scientific investigation. 
A few words now concerning the principles which determine 
success in maintaining the necessary conditions for life in 
aquarium tanks. It is needless to review the gradual progress of 
knowledge concerning aquaria. It is well known at the present day 
that if the proper balance of animal and plant life be maintained in 
an aquarium, the products of respiration of the animals are removed 
from the water by the growing plants, and oxygen is given out in 
return. Although this perfect balance can be readily maintained - 
in small tanks at home, it is not practicable to depend on plant life 
to aerate the water on a large scale. In the year 1861 Mr. Barnum 
procured two living whales, some sharks, and one or two other 
inhabitants of the deep, which he kept for some time in tanks 
supplied with salt water from the river. This was the first public 
marine aquarium in America, and the method now in most favor 
for keeping animals alive in tanks 1s the same as Mr. Barnum then 
adopted, except that instead of pumping the water directly from its 
source, a supply is stored in underground cisterns, from which it is 
continuously pumped into the tanks and allowed to flow back into 
the cisterns. As the water flows from place to place, it becomes 
well aerated ; and the same water may be used for years. In the 
Crystal Palace aquarium the exhibition tanks have a capacity of 
20,000 gallons, while the reservoir contains 100,000 gallons more. 
It is a question whether such a large reserve supply is necessary, or 
indeed, whether any considerable volume of water besides what is 
in the tanks need be kept. There are two benefits to be derived 
from it, however, first, the temperature of a large volume in the 
cistern must remain tolerably constant throughout the year, and 
second, any disturbance in’ one of the tanks, causing the water to 
become foul or turbid, can be immediately remedied by drawing 
the water off into the large cistern, when it mingles with such a 
comparatively large volume that it can do no harm. ‘The loss of 
