CLASS VEKMES: OKDEB ANNTJLATA. 



237 



animal is withdrawn into the tube. Other worms nearly 

 allied to Serpula form a tube by cementing together grains 

 of sand and bits of broken shells. 



The Lumbricidse (Common Earth or Angle-worms) are 

 wanting in gills, but minute apertures on the sides com- 

 municate with internal respiratory sacs, on the walls of 

 which the blood circulates for aeration. Tiny spines directed 

 backward enable the worm to force its way through the 



Fig. It06. 



. Lumbrlcus terrestrls, Angle or Earth- 

 worm. h. Anterior segments magni- 

 fied, showing bristles directed back- 

 ward ; c. Egg^ enclosing two young ; 

 d. Escape of young from egg. 



Hfr&do medicindlis. Leech, Europe. 



earth. Digesting the organic 

 matter in the dirt it eats, the 

 rejected "worm-casts "are of service in the garden, and often 

 cover barren tracts with a layer of productive mould. It is 

 oviparous a single egg frequently containing two embryos. 



