FOOD. 289 



tliem cannot be developed witliout light; if, then, tliis 

 Le denied, the plants must wane and die. Now the 

 opacity, as I have intimated, consists of the living 

 germs of green plants ; and these, on being deprived 

 of light, gradually die away ; after which the w^ater is 

 quite fit for use again. I have myself instituted 

 experiments on the subject, and, so far as I have 

 proceeded, my results agree with those of Mr. Lloyd ; 

 except that I have found a seclusion of several months 

 necessary. This was, however, in the winter. 



Cloudiness may often be removed by the action of 

 living animals. The Bivalve Mollusca collect the 

 organic particles that float in the water, as the cur- 

 rents pass over their capacious gills, and either feed 

 on them or consolidate them into cylindrical rolls, 

 which fall to the bottom, enveloped in mucus. Hence 

 they are of great service in making tm'bid water limpid 

 and bright. An Oyster or two, according to the size 

 of the vessel, will answer exceedingly well, as they 

 are very hardy, and can be procured alive anywhere, 

 and almost at all seasons. 



Food. — I am continually asked, lioic, witli what, 

 and how often I feed my animals. My invariable 

 reply is — " Not at all." I do not find that they need 

 any supply but what they procure for themselves. In 

 a well-stocked and established Tank, the vegetable- 

 feeders find a sufficient pabulum in the ever-growing 

 weed ; and all the carnivorous species are maintained 

 in condition by the hosts of Infusoria and Ento- 

 MOSTRACA that are always swarming. The lens shows 

 these tiny creatures to be abundant in every collection 

 of water that has been kept for a short time ; and as 



u 



