EARTH-WORMS AND THEIR WORKS. 



299 



_. -'^T-'f- 



O 



IV 









7 a 



by bringing earth to the surface in their castings, to be blown away by 

 the winds and washed away by the rains into the valleys. They are 

 extraordinarily numerous. Hensen says there are 53,767 of them in 

 an acre of garden-soil, and Mr. Darwin is willing to allow half that 

 number, or 20,886, to the acre in 

 corn-fields and pasture-lands ; and 

 as in many parts of England a 

 weight of more than ten tons of 

 dry earth annually passes through 

 their bodies and is brought to the 

 surface on each acre, the whole 

 superficial bed of vegetable mold 

 must pass through them every 

 few years. By triturating this 

 earth, by subjecting its minerals 

 to the action of the humus acids, 

 and by periodically exposing the 

 mold to the air, they prepare the 

 ground in an excellent manner 

 for the growth of fibrous-rooted 

 plants and for seedlings. The 

 bones of dead animals, the harder 

 parts of insects, the shells of 

 land-mollusks, leaves, twigs, etc., 

 are before long all buried be- 

 neath the accumulated castings 

 of worms, and are thus brought in 

 a more or less decayed state with- 

 in reach of the roots of plants. 

 Leaves are digested by them and 

 converted into humus. Their bur- 

 rows, penetrating to a depth of 

 five or six feet, are believed to 

 aid materially in the drainage and 

 ventilation of the ground. They 

 also facilitate the downward pas- 

 sage of roots of moderate size, 

 which are nourished by the hu- 



pi 





lJ j. ,, iLi--L' , i: , l. 





O a 



K s 

 ~ ? 

 a - 

 ft = 



** 



_ - 



K _, 



c r 



O 5 



o 



It 



S3 

 oS 

 c /. 



W n 



S = 



mo 





m - s 



z -~ 



8-"* 



f- 



- i: 



ti. o 



- - a 

 f- = ^: 

 P = 3 



fJl 



igg 



WAS 



I a a 







mus with which the burrows are 



lined. Many seeds owe their germination to having been covered by 

 castings ; others, buried more deeply, lie dormant till they are brought 

 xinder conditions favorable to germination. " The plow," says Mr. 

 Darwin, in conclusion, "is one of the most ancient and most valuable 

 of man's inventions ; but long before he existed the land was in fact 

 regularly plowed, and still continues to be thus plowed, by earth- 

 worms. It may be doubted whether there are many ether animals 



