THE MARINE AQUARIUM. 151 



out informing us whether the plant be large and- the 

 animals small, or vice versa. One full-grown plant of Ulva 

 or Valisneria will give off enough oxygen for two or 

 three minnows ; but one plant of Entcromorpha or Le/nna, 

 will certainly not supply enough oxygen for one fish, how- 

 ever small, be he even a stickleback of half an inch 



long. 



As I have remarked before, at certain seasons of the 

 year, the water of the Aquarium will become opaque 

 from myriads of the green spores or seeds of the algcs, 

 and to get rid of these, Mr. W. A. Lloyd recommended 

 a removal of the water from the tank and shutting it 

 up in a dark place, where the spores cannot get the 

 light necessary to their growth and, therefore, die. I 

 have sometimes found that if there be no fish in the 

 tank, this green cloud will settle to the bottom and, 

 after a while, supply us with a harvest of young plants 

 of Ulva or Enter omorpha. 



When putrefaction has set in among, our live stock, 

 it will progress with alarming rapidity, and in a few 

 hours the stench from the tank may be so strong that 

 it cannot be borne. The best thing then to do will 

 be to remove all stock that still remains alive, and, 

 washing it in a pail of clean sea water, place it in a 

 jar or glass dish to save it. As we may be some way 

 from the sea, we shall, of course, wish to save the sea- 

 water if we can, for the water itself never decays, it 

 is only the particles of animal matter diffused through 

 it that are causing the trouble. Mr. Gosse recommended 

 putting the water that is in a vessel, into some out- 



