SEVENTH ANNUAL REPORT. 89 



and artificial aeration has been practically discontinued. The 

 feed pipes supplying water in jets are usually so constructed 

 that more force, and consequently greater aeration, can be secured 

 by increased pressure. The jets are applied either to the open 

 surface of the tank, or are received in large glass tubes in the 

 corners of the tanks leading to the bottom, the latter serving to 

 make the circulation more effective. In some cases they were 

 supplied with jets at each end. 



The cisterns and exhibition tanks everywhere are of masonry 

 and cement. In some cases the water-flow is continuous from 

 tank to tank throughout the exhibition series, while in others 

 each tank has its separate outlet. 



A noticeable feature of the exhibition tanks in European 

 aquariums is their large size, fishes especially being given con- 

 siderable room for movement. In some cases two or three tanks 

 are connected, giving a good range for the more active species. 



At Plymouth the largest tanks are 15 feet long, 8 feet wide, 

 and 5 feet deep. Two of these are connected, giving the fishes 

 a swimming range of 30 feet. At Amsterdam the larger tanks 

 are 7 feet long with single glass front plates a,]/^ feet high, 

 having apparently a width of about 5 feet. The largest of three 

 connected tanks was 8>^ feet long. The largest glass plates in 

 use are two inches thick, the others being somewhat lighter. 



Some of the grotto-like exhibition tanks at Berlin extend back 

 apparently 10 feet from the glass front. Three tanks at the 

 Naples aquarium are connected, giving a swimming range for 

 large fishes of about 30 feet, the width being about 12 feet. 



There are 26 tanks in this aquarium, the glass fronts of the 

 tanks being 6 feet high. 



The Brighton aquarium has 41 exhibition tanks. These are 

 mostly II feet long by 10 feet wide. Two of the tanks here 

 are of exceptional size, one being 130 feet long and 40 feet wide, 

 and the other 50 by 30 feet. 



At Paris the central tanks are 12 feet deep, although not of 

 great dimensions otherwise. This aquarium is underground, 

 occupying the site of an old quarry. Its exhibition tanks, 23 

 in number, extend to the park above, where their surfaces appear 

 as open ponds, the collections being viewed from the wide un- 

 derground corridors. The tanks — open to the air and sun — 

 permit a good growth of fresh-water plants. There is nothing 

 in the park to indicate the presence of the aquarium beneath, 

 which has cave-like entrances leading down from the adjoining 

 street. 



