88 NEW YORK ZOOLOGICAL SOCIETY. 



and salt-water collections ; while the Paris aquarium is limited 

 to fresh-w^ater species. At Berlin the salt water in use is man- 

 ufactured in the establishment. It has been used since 1869, 

 being much cheaper than natural sea water; at the other aqua- 

 riums it is pure sea water stored in underground reservoirs or 

 cisterns. As a rule salt water is pumped from the reservoirs to 

 the exhibition tanks, whence it flows through sand filters back 

 to the reservoirs. Although supplied with filters the aquariums 

 at Naples and Plymouth get good results without filtering the 

 water. The former has three reservoirs and the latter two. The 

 supply of sea water is secured at the most favorable times, that 

 is, when the adjacent bays are clearest and freest from impuri- 

 ties, and as seen in the exhibition tanks is always clear and per- 

 mits very satisfactory viewing of the collections. 



In most cases the exhibition tanks are fed by Jets, the water 

 striking the surface with considerable force and carrying air 

 down with it. 



The use of pure sea water permits of the exhibition of many 

 kinds of invertebrates that would not live in brackish water. At 

 Naples there are specimens of anemones that have lived in the 

 tanks for years. 



The reservoirs are constructed in series of two or three, water 

 being pumped from them in turn after a period of settling. The 

 reservoirs are emptied and cleaned once or twice a year. At the 

 Naples aquarium an abundance of minute life — copepods, etc. — 

 lives and propagates in the water supply, furnishing more or less 

 food for the smaller forms of invertebrates in the exhibition 

 tanks, and perhaps freeing the water to some extent of refuse. 

 In all cases the reservoirs are kept in total darkness, and are 

 located below the exhibition tanks, so that considerable aeration 

 is secured by the falling of the water back into them. 



Among the officials of European aquariums the consensus of 

 opinion is that the best results are secured with closed circula- 

 tion, that is, with a permanent stored supply of sea water. 

 Varying conditions of temperature and density, and practically 

 all sediment are thus avoided. 



In European aquariums generally the collections consist of 

 local species, or at least of such forms as are adapted to the 

 customary temperatures of the cisterns, and they are maintained 

 without either heating or cooling devices. The salt water is, 

 therefore, warmer in winter and cooler in summer than the fresh 

 water taken from city pipes. Some of the institutions were sup- 

 plied with aerating machinery, but it was nowhere found in use. 



I 



