ROCKWORK FOR AQUARIA. 41 



paste with boiled linseed oil, and applied unstintingly . 

 A little rockwqrk is always an additional element of 

 attraction in an aquarium, especially if fish or amphi- 

 bia are kept. In fresh- water aquaria, however, it is 

 never required to the extent it is in marine. When 

 built up loosely, the darker places afford a screen 

 from a too intense light, and those creatures which 

 cannot bear it will soon discover such retreats. But 

 this adaptation applies more to marine animals than 

 the fresh-water forms of which we are especially 

 treating. Newts love to crawl upon a stone or piece 

 of rockwork projecting above the water, in order to 

 bask in the sun; but this they will do if the water 

 plants are strong enough to bear them on the surface 

 of the water. The best and most harmless material 

 for rockwork is pieces of pumice-stone, fragments of 

 melted glass bottles, and such fragments of vitrified 

 bricks as may be picked up in any brick-kiln. These 

 should be fastened together with Portland cement. 

 In order to make the contents of the tank as light as 

 possible, one or two inverted flower-pots may be 

 fastened to the bottom. If the inverted edges be so 

 broken as to form a passage through, then the interior 

 will serve as a dark cave to any of the animals re- 

 quiring such a retreat. The holes (now uppermost) 

 should not be filled up, for the water within the 

 inverted pot will be kept colder, and thus a healthy 

 current action between it and the surface water may 

 be set in action through the holes. Flower-pots thus 



