VI ANNELIDA 81 



most valuable of man's inventions ; but long before he existed 

 the land was in fact regularly ploughed and still continues 

 to be thus ploughed by earthworms. It may be doubted 

 whether there are many other animals which have played so 

 important a part in the history of the world as have these 

 lowly organised creatures." 



River-worms, or Eed-worms (TWij/ea; rivulorum), 

 River-wonns ^^^ thread-like aquatic forms, very common in 

 shallow pools, streams, and rivers. Tlie body is 

 from 1 to 1^ inches long, and is bright red, owing to the 

 transparency of the skin which allows the blood-vessels and 

 even the other internal organs to be clearly seen through it. 

 They live in colonies in the soft mud below the water, and 

 when undisturbed they will project their tails out of the mud, 

 waving them about so that they form a red patch that quickly 

 attracts attention ; if alarmed they at once retreat into their 

 mud burrows. 



They breed very rapidly, and form a natural and excellent 

 food for fish and other carnivorous aquatic creatures. 



To keep them healthily in captivity, they must be given 

 plenty of soft mud in which to burrow, and the water above 

 them must not be more than 3 or 4 inches deep. 



Earthworms and River-worms are Chaetopod Annelids, or 

 Bristle-footed Ringed-worms, but there are other forms of the 

 same class which differ from- them in the greater, complexity 

 of their body-structure, though they still have the same 

 characteristic bristles or chaetae. These are the marine 

 worms which are described in the next chapter. 



Practical Work on Earthworms 



1. Earthworms should be kept in a " wormery," made of a box 

 having one or two glass sides that can be covered or uncovered at 

 will. This box should be about 12 inches deep ; it should be filled 

 with soils of markedly different appearance, in well-defined layers ; 

 the way in which the lower soils are brought up to the surface 

 can then be observed. The earth should be kept slightly damp, 

 and food of different kinds left on the surface of the soil, and the 

 treatment of it by the worms watched. Some of the worms are sure 

 to make their burrows against the glass sides of the box if these 

 are kept covered, and the structure and position of them should 

 be noted. 



VOL. I G 



