152 now TO WORK 



giving off bubbles of oxygen gas, fish, water insects, &c. ; may be 

 introduced. A plant or two of the floating " Frogbit " is useful for 

 giving support to such species as come occasionally to the surface. 



In the case of both fresh-water and marine aquaria it must be 

 "borne in mind that a proper amount of light is required which 

 should be admitted from above as well as on one side of the vessel. 

 If there is not light enough, the plants droop and do not give off air 

 bubbles, while if there is too much light there will be a more abun- 

 dant growth of confervae upon the sides of the vessel than the 

 scavenger molluscs can keep under. It must also be borne in mind 

 that animals must be kept in what has been called " amicable 

 groups," or wholesale destruction will ensue. 



Minnows, sticklebacks, and eels, are the fish best suited for fresh- 

 water aquaria, but of course must not be kept in such as are used 

 for watching the various stages of development of other animals. 

 Small eels are most interesting objects, and the student will be 

 interested in watching the pulsations of the venous heart in the tail 

 of the animal. 



Marine aquaria require more attention in their construction than 

 those for fresh water, and as a greater variety of forms may be 

 associated they should be made large. A marine aquarium, capable 

 of holding from five to ten gallons, is a convenient size and will 

 succeed well. The bottom and sides should be of slate, the back 

 and front only being of glass cemented into grooves made in the 

 slate, not simply abutting against a shoulder and cemented, or a 

 continual leakage may occur. I have made excellent joints with 

 the aid of the lime and India-rubber cement, p. 52, to bed the 

 glass in, this being covered with a mixture of white and red lead 

 forced in together with some fine tow or cotton wool. The aquarium 

 should be covered with a glass top fitted to a beading of perforated 

 zinc, so as to admit air but keep out dust. The form should be such 

 as to allow a large area of surface to be in contact with the air in 

 relation to the bulk of water. Rock work should be built up at the 

 back so as to cut off an unnecessary amount of light, and should be 

 arranged in such a way as to present tiers of resting places for the 

 animals. The basis may be formed of coke which is advantageous 

 on account of its lightness, but this is to be faced with flakes of 

 granite, limestone, and sand rock, put together with hydraulic cement 

 to produce a more picturesque appearance. It is, however, better not 

 to use cement at all. 



The tank so far prepared should be first filled with fresh water to 

 remove all soluble matters from the cement and rockwork. After resting 

 for a day or two, the water must be drawn off with an India-rubber 



