254 CRUSTACEA, ECHINODERMS, ETC. 



CHAPTER XV. 



CRUSTACEA, ECHINODERMS, ANNELIDS, ETC., OF 

 MARINE AQUARIA. 



ONE of the most important advantages which large 

 aquaria, aerated by constant jets of water, possess, 

 is the great variety of marine animals, vertebrate and 

 invertebrate, which may be kept in them. Not only 

 may they be so selected as that one group shall not 

 harm another, but much of the labour and anxiety 

 likely to occur from the pollution of the water by 

 decomposing food or dead animals, may be prevented 

 by merely including certain omnivorous creatures 

 which will clear away such garbage and consume 

 it as food. Some of the carnivorous mollusca (the 

 whelks, for instance) are useful in this respect, but 

 many of the Crustacea are even more so. The latter, 

 also, are more lively animals, and never fail to cause 

 amusement by their grotesque and serio-comic habits. 

 One cannot witness the rude gambols of lobsters and 

 crabs without feeling that the element of humour is 

 not merely a subjective condition of the human mind, 

 but has an objective existence in nature. 



Of all the useful and interesting scavengers, none is 

 more so than the hermit crab (Pagtirus Bernhardus\ 



