152 MARINE AQUARIA FOR ROOMS. 



cleans the glass and rocky surfaces. Like the peri- 

 winkle, it will often crawl above the level of the water. 

 Mr. W. R. Hughes recommends Mr. Edwards's 

 plan of having a parlour tank with a sloped back, and 

 we thoroughly agree with him that this is by far 

 the best arrangement! . It has the merit of enabling 

 the animals to adjust themselves from the shal- 

 lowest to the deepest parts according as their habits 

 require ; and offers a minimum space for the recep- 

 tion of the rays of sunlight. Over this sloping 

 back, or bottom, rockwork is to be arranged, as 

 already described. The sloping bottom may be per- 

 forated, so that the tank is divided equally into a dark 

 and a light chamber. Such an arrangement sets up a 



Fig. 113- 



Section of Slope-back Tank, showing Dark Chamber. 



slow, natural circulation, whilst it prevents the undue 

 development of the spores of algae. Another means 

 of promoting circulation is that of having syphons, 

 which may be made to gently pour in the tank a 

 fine stream of water from a jar placed above. If 

 the current is made to flow a few inches through 4he 



