154 GLAUCUS ; OR, 



nibble the green ulva?, but when the fihn of 

 young weed begins to foi'm, you will see it 

 mown off every morning as fast as it grows, in 

 little semicircular sweeps, just as if a fairy's 

 scythe had been at work during the night. 



And a scythe has been at work ; none other 

 than the tongue of the little shell-fish ; a descrip- 

 tion of its extraordinary mechanism (too long to 

 quote here, but which is well worth reading) 

 may be found in Gosse's Aquarium.* 



A prawn or two, and a few minute star-fish, 

 will make your aquarium complete ; though you 

 may add to it endlessly, as one glance at the 

 salt-water tanks of the Zoological Gardens and 

 the strange and beautiful forms which they con- 

 tain will prove to you sufficiently. 



You have two more enemies to guard against ; 

 dust and heat. If the surface of the water be- 

 comes clogged with dust, the communication be- 

 tween it and the life-giving oxygen of the air is 

 cut off; and then your animals are liable to die, 

 for the very same reason that fish die in a pond 

 which is long frozen over, unless a hole be broken 

 in the ice to admit the air. You must guard 

 against this by occasional stirring of the sur- 



*P. 34. 



