THE MAEINE AQUARIUM 53 



always be regarded with suspicion. Such a scum should be 

 removed with the aid of absorbent paper, since it tends to prevent 

 the absorption of oxygen from the air ; and, should the water be 

 tainted in the slightest degree, it should be changed at once, or, if 

 this is not practicable, air should be driven into it for some time 

 by means of a syringe with a very fine nozzle. Such precautions, 

 however, are not so urgently needed when the aquarium contains 

 crustaceans only, for the majority of these creatures suffer less 

 than others in the tainted sea water, some even being apparently 

 quite as comfortable in this as in a supply fresh from the sea. 

 Sea-weeds exhibiting the slightest tendency to decay must be 

 removed at once ; and, as regards the feeding of the animals, one 

 must be careful to introduce only as much food as is required for 

 immediate use, so that there be no excess of dead organic matter 

 left to putrefy. Some of the marine animals obtained from our 

 shores feed entirely on the minute and invisible organisms that 

 are always present in the sea water, and others subsist principally 

 on certain of the weeds. Many, however, of a more predaceous 

 disposition, capture and devour living prey, while some, and more 

 especially the crustaceans, are partial to carrion. If, therefore, 

 the observer desires to study the ways in which the various 

 creatures secure and devour their food, he should introduce into 

 his aquaria live marine worms and other small animals, and also 

 small pieces of fish or flesh. 



We will now pass on to the more serious undertaking of the 

 construction and management of a permanent salt-water aquarium. 



The first point to decide is, perhaps, the size of the proposed 

 vessel, and this will in many cases be determined partly by a 

 consideration of the space at one's disposal, and of the apartment 

 it is intended to occupy. If it is to be placed in a drawing-room 

 or other ordinary apartment of a dwelling-house, preference should 

 be given to a window facing the north in order to avoid the direct 

 rays of the sun, but perhaps no situation is more suitable than 

 a cool conservatory in the shady part of a garden ; and in either 

 case a strong table or other support should be provided, of a form 

 and size adapted to those of the aquarium to be constructed. 



Various materials may be used in the construction of such an 

 indoor aquarium, and we shall deal with two or three different 

 types, so that the reader may make his selection according to his 

 fancy, or to his mechanical ability, if he intends that it shall 

 be of his own construction. 



