150 GENERAL MANAGEMENT OF 



remarked, the necessity for aeration marks error in manage- 

 ment, except when you have stock for which no proper 

 receptacle is at hand or any such special contingency." 



When wc use the artificial sea- water and, for the pur- 

 pose of " seasoning " it, place in it Ulva and Enteromorpha, 

 these plants, after a time, often become light-colored and, 

 at last, quite white, which is a sign of death aud decay, 

 and should be at once attended to by removing the 

 plants and replacing them by others. When the water 

 has become well seasoned, we shall not be so likely to 

 see this happen, unless something else in the tank be 

 out of order. If, however, any of the red alga, be intro- 

 duced before the proper time, that is to say, where the 

 Aquarium has not been in vigorous action some time, 

 they will be sure to decay and color the water of a 

 brilliant red, which must kill all the animals, beginning 

 with the hermit crabs, who arc always the first to show 

 signs of something being wrong in the economy of the 

 collection. Ono of the first signs of decay in the red sea- 

 weeds is their turning of a bright orange in spots and 

 near to the edge. 



As to the amount of plants necessary to aerate the 

 water for a given number of animals, it is very difficult 

 to present anything that may be laid down as a rule on 

 that point. The knowledge required so to adjust the 

 vegetable to the animal life in order to balance them, 

 can only be learned by practice. We should always be 

 certain of putting in enough vegetable matter. Some 

 writers pretend to lay down a rule for its introduction, 

 saying that one plant is sufficient for two animals with- 



