20 THE AQUARIAN NATURALIST. 



ment of thin silk gauze of a blue colour, or by layers 

 of tissue-paper tinged blue and green, sometimes oiled 

 to make them more transparent ; or coloured varnishes, 

 blue, and blue and yellow, mixed to the required tint, 

 will answer the same purpose . These materials should 

 be applied to the surface of the glass, or interposed 

 between the source of light and the water in such a 

 way, that the whole of the light which directly illu- 

 minates the aquarium may be tinted of the proper 

 colour. 



To such an extent has this plan succeeded, that 

 portions of red sea-weed, which had become thickly 

 mantled with the brown and green confervoid growths 

 above alluded to, and which had not exhibited the 

 least signs of vitality, on being placed in a small glass 

 jar, arranged with tinted and oiled tissue-paper, soon 

 lost the whole of this parasitic growth from its gra- 

 dually decaying, and being then consumed by the 

 mollusks; the fronds, assuming their deep crimson 

 hue, becoming perfectly clear, and throwing out new 

 shoots and leaflets. 



Sea- water may be preserved for a long period in a 

 perfectly efficient and healthy state under some cir- 

 cumstances without the introduction of growing vege- 

 tation, and this simply by exposing a very extended 

 surface to the action of the air, and at the same time 

 limiting its depth. 



The means whereby this may be accomplished, con- 

 sist in the employment of shallow circular stoneware 

 pans of about eighteen inches internal diameter by 

 five inches deep ; these are filled for about two inches 

 with water, the bottom is supplied with sand and 



