WOEMS. 



127 



The Oligoclimta are represented by the common Earthworm 

 (92), the influence of which in the formation of mould and in the 

 general ploughing of the soil was carefully investigated by Mr. Darwin, 

 and by a few other worms (122-127) ; the little TuUfex rivulorum 

 (Bloodworm), which owes both its red colour and its ability to dwell 

 in mud, which is so poor in oxygen as to be unfit for respiration, to 

 the same chemical compound as that which gives the red colour to 

 our blood and carries the oxygen of respiration all over the body. 



The Hirudinea, or Leeches, are often said to be distinguished 

 from the GhcRtopoda by the absence of bristles ; but, as a fact, 

 AcanthoMella (Figs. 21 and 22) has very well marked bristles. They 



Fig. 21. 



Fia:. 22. 



e — s 



s~\ 



Acanthohdella : e, eyes ; cli, chsetsd ; s, sucker. 



always have a sucker at the hinder end of the body by which they are 

 attached to their prey ; they are found in fresh water (Fiscicola), on 

 sea-fishes (as FontoMella), or in moist places, as the Leech (Hinido) 

 (130-134). The last-named has three jaws, armed with as many 



