WORMS 



165 



taken into the burrows and eaten, while the waste is brought to 

 the surface with the earth as castings. 



Economic Value. This method of feeding loosens and enriches 

 the soil, performing about the same work as does the farmers' 

 plow, though to a greater extent, for the worms are found in all 

 parts of the world, in such numbers that they pass through their 



HOST 



FIG. 51. Life history of beef tapeworm. A, adult tapeworm in intestine of 

 man; B, proglottid full of eggs on ground; C, eggs on ground; D, six-hooked 

 larva (onchopore) set free and bores through tissues of cow; E, cysticercus 

 or bladderworm, hi cow's flesh; F, young tapeworm in man. From Pearse. 



bodies an average of ten tons of soil per acre, every year, and thus 

 do an incalculable service to the farmer. Thus the humble earth- 

 worm, whose function may have seemed to be to furnish bait for 

 fishing, now is seen to be a very useful member of society. It 

 has, however, some very bad relatives, which do a great deal of 

 harm and therefore require special mention. 



