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AQUARIA

in a condition healthy enough to breed. Much experience however, has been gained of late years at considerable expense, both at home and abroad. In starting a marine aquarium of whatever size, it should be obvious that the first consideration must be a supply of the purest possible water, as free as may be, not only from land-drainage and sewage, but also from such suspended matters as chalk, fine sand, or mud. This is most ideally and economically secured by placing the station a few feet above highwater mark, in as sheltered a position as possible, on a rocky coast, pumping from the sea to a large reservoir above the station, and allowing the water to circulate gently thence through the tanks by gravity (Banyuls). At an inland aquarium (Berlin, Hamburg), given pure water in the first instance, excellent if less complete results may nevertheless be obtained. The next consideration is the method by which oxygen is to be supplied to the organisms in the aquarium. Of the two methods hitherto in use, that of pumping a jet of air into tanks otherwise stagnant or nearly so (Brighton), while supplying sufficient oxygen, has so many other disadvantages, that it has not been employed regularly in any of the more modern aquaria. It is, however, still useful in aerating quite small bodies of water in which hardy and minute organisms can be isolated and kept under control. In the other method, now in general use, SUP The' library contains about 9000 volumes, which students use a fine jet of water under pressure falls on to the surface with the help of a slip catalogue, arranged according to authors. of the tank; this carries down with it a more than The station has published at intervals since 1879 two periodicals sufficient air-supply, analysis^ showing in some cases a treating of the organisms of the Mediterranean. One is fauna und Flora des G-olfes von Neapel, the other Mittheilungen aus der higher percentage of oxygen in aquarium water than m Zoologischen Station zu Neapel. The former consists of mono- the open sea. o-raphs in which special groups of animals and plants are most This water supply is best effected by gravity from exhaustively treated and the Mediterranean species portiayed reservoirs placed above the tanks, but may be also according to life in natural colours up to the present time twenty-one zoological and five botanical monographs have ap- achieved by direct pumping from low reservoirs or from the peared, making altogether 1200 4to sheets with_ about 400 plates. sea to the tanks. Provided that an unlimited supply of Of Mittheilungen, which contain smaller articles on organisms pure water can be obtained cheaply, the overflow from the of the Mediterranean, fourteen volumes in 8vo have been pub- tanks is best run to waste ; but in aquaria less fortunately lished. The station also publishes a Zoologischer Jahresbericht, which at first treated of the entire field of zoology, but since 1886 placed, it returns to a storage low-level reservoir, from has been confined principally to Comparative Anatomy and which it is again pumped, thus circulating round and round Ontogeny; it appears eight to nine months after the end of the (Naples, Plymouth). The storage reservoirs should be m year reported. The Guide to the Aguarium, with its descriptions^ all cases very large in comparison with the bulk of water and numerous pictures, is meant to give the lay visitoi an idea of in circulation; if practicable, they should be excavated in the marine animal world. . ... There are about forty officials, amongst them six zoologists, rock, and lined with the best cement. There is no reason one physiologist, one secretary, two draughtsmen, one engineer. why they should not be shallow, exposed to light and air, The station is a private institution, open to biologists of all and cultivated as rock-pools by the introduction of seanations under the following conditions : there are agreements with the Governments of Austria, Baden, Bavaria, Belgium, weeds and small animals, but they must then be screened Hamburg, Holland, Hesse, Italy, Prussia, Russia, Saxony, from rain, cold, and dust. The pumps used m circulation Switzerland, Hungary, Wurtemburg, the province of Naples, and will be less likely to kill minute animals if of the plunger the Universities of Cambridge, Oxford, Strassburg, Columbia or ram type, rather than rotary, and should be of gunCollege (New York), and the British Association for the Advancement of Science, the Smithsonian Institute, and a society of metal or one of the new bronze-alloys which take a patina women in the United States of North America (formerly also with in salt water. For the circulating pipes many materials Bulgaria, Rumania, Spain, the Academy of Sciences in Berlin, have been tried. Vulcanite is not only expensive and Williams College, University of Pennsylvania), by virtue of which the Governments and corporate bodies named have the right, on brittle, but has other disadvantages; common iron pipes, payment of £100 per annum, to send a worker to the station ; coated internally with cement or asphalt, or glazed inthis places at his disposal a “table” or workplace, furnished ternally, with all unions and joints cemented, have been with all the necessary appliances and materials as set down in the used with more or less success. Probably best of all is agreement. At present there are agreements for thirty-three tables, and since the foundation of the station nearly 1200 common lead piping, the joints being served with redbiologists have worked there. The current expenses are paid out lead ; water should be circulated through such pipes till of the table-rents, the entrance fees to the public aquarium, and they7 become coated with insoluble carbonate, for some an annual subvention paid by the German Empire. time before animals are put into the tanks. For small In England a station on similar lines, but on a smaller installations glass may be used, the joints being made with scale, is maintained at Plymouth by the Marine Biological marine glue or other suitable cement. In building the tanks themselves, regard must be had Association of the United Kingdom, with the help of subsidies from the Government and the Fishmongers’ to their special purposes. If intended for show-tanks for popular admiration, or for the study of large animals, they Company. Little difficulty is experienced in maintaining, breeding, must be large with a plate-glass front; for ordinary scienand rearing fresh-water animals in captivity, but for tific work small tanks with all sides opaque are preferable many various reasons it is only by unremitting attention from every point of view. According to their character, and foresight that most marine animals can be kept even size, and position, fixed tanks may be of brickwork, alive in aquaria, and very few indeed can be maintained masonry, or rock, coated in each case with cement,

almost constant pressure, into the tanks. The water circulated in this manner contains by far the largest number of such animals as are capable of living in captivity ^ food n00^1^. Some of them even increase at an undesirable st0 rate, an times happens that young Mytilus or Ciona P, UIUje in laying these, therefore, due regard must be had to the arrangements for cleaning. For the cultivation of very delicate animalsTt is necessary to keep the water absolutely tree from harmful bacteria ; for this purpose large sand-filters have lately tfeen placed in the system, through which the water passes alter leaving the cisterns. Each of the smaller cisterns which are fixed in the'work-rooms, consists of two water-tanks, placed one the other ; their frames are of wrought iron and the walls generally of o'lass. Vessels containing minute animals can be placed between these two tanks, receiving their water through a siphon from the upper tank ; the water afterwards flows away into the lower tank P {he twenty-six tanks of the public aquarium (the largest ot which contains 112 cubic metres of water) have stone walls the front portion alone being made of glass. As the tanks hold a very large number of animals in proportion to the quantity ot water, they require to be well aerated. The pipes through which the water is conducted are therefore placed above the surface of the water, and the fresh supply is driven through them under strong pressure. A large quantity of air in the form of fine bubbles is thus taken to the bottom ot the tank and distributed through the entire mass of water. Should the organisms which it is desired to keep alive be very minute, there is a danger of their bein^ washed away by the circulating water. To obviate tins, either the water which flows away is passed through a strainer, or the water is not changed at all, air being driven through it by means of an apparatus put into motion by the drinking-water