A NEW PRINCIPLE OF AQUICULTURE. 765 



to the bulk is large, respiration may be continuous and direct without special 

 internal apparatus, and, likewise, shallow water with a large expanse of surface 

 has been found by experiment to need no aeration in order to maintain animals 

 alive for a long time. On the other hand, in bulky animals, the respiratory 

 apparatus provides always for the elimination of gaseous products of metab- 

 olism as inevitably as it provides for the acquisition of oxygen. Therefore 

 the bringing of the lower strata of water continuously to the surface fulfills 

 two necessary requirements. 



For keeping larval forms which are not exceedingly minute, windows 

 covered with screens about 16 meshes to the inch in the bottom of the cars 

 allowing for intake, and similar ones in the sides for the exit of water, are satis- 

 factory. A much finer mesh can be used in this case than would ordinarily be 

 practicable, because the water is drawn in through the bottom screens with 

 considerable force by the upward tendency of the current. It is possible by 

 means of a filter device, which will be described hereafter, to hold fry which 

 would pass through even very fine screens. 



The rotary upward current keeps the particles of food suspended in the 

 water even when artificial food heavier than water is used. When, on the 

 other hand, a pelagic live food is used, it is also, of course, readily available, 

 because it is kept in motion and suspended. The important problem of the 

 distribution of food for pelagic forms is solved by this method in a most satis- 

 factory manner. 



ADAPTABILITY OF THE METHOD. 



Before describing the apparatus as at present installed at our station, 

 where it is applied to the hatching and rearing of young fishes and inverte- 

 brates, a word should be said to indicate its general adaptability to various 

 requirements. In any protected body of water, whether river, lake, pond, or 

 in the ocean itself, the apparatus can be quickly and cheaply installed. For 

 experimental work the containing cars may be small. Dr. V. E. Emmel, by 

 use of this method, succeeded for the first time in the difficult task of making 

 mutilated lobsters of the first stage live to regenerate their appendages. His 

 apparatus consisted of an ordinary "paper" bucket provided with screens and 

 the apparatus for keeping the water in motion. On the other extreme the 

 units in our regular installation at Wickford are square boxes measuring 10 

 feet on a side and 4 feet in depth, with capacity approximately 12,000 liters 

 (fig. 4, 5, 6, pi. xci, xcii). The capacity of a plant of this sort is capable of 

 unUmited extension by the addition of units. At present the plant at Wickford 

 has a capacity of 24 units of the size mentioned. The method is capable of 

 application to aquatic animals, fresh water or marine, varying in size from 

 those literally microscopic to those of a foot or more in length. We do not 



