MISCELLANEOUS ANIMALS 425 



mould over any such expanse has passed, and will again pass, every 

 few years through the bodies of worms. The plough is one of the 

 most ancient and 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 earth-worms. 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 organized creatures. 



Earthworms burrow into the soil to a depth of from 

 three to eight feet, making channels for water, air, and the 

 roots of plants to penetrate. In order to study this sub- 

 ject have each child count the worm burrows in a square 

 foot of ground. They may be found by the little piles of 

 castings at the mouth of each burrow and also by the 

 leaves and grass that the worms have pulled into the 

 opening to feed upon and to close the door. If a box 

 be turned over the area a day or two before the count 

 is made, so that the surface will not be disturbed or the 

 castings washed away by rains, the burrows will be more 

 easily found. 



Next fill a small aquarium with fine sand or garden 

 earth and place three or four large worms on the surface. 

 Study the way they burrow. After they have established 

 themselves in their burrows scatter a little grass or a few 

 dead leaves on the surface and observe from day to day 

 what the worms do with them. If sand and leaves be 

 used, and the aquarium be left for a number of weeks, 

 the formation of vegetable mould may be observed in a 

 striking manner. 



Von Hensen placed two worms in a vessel eighteen inches in 

 diameter, which was filled with sand, on which fallen leaves were 

 strewed ; these were soon dragged into their burrows to a depth of 

 three inches. After about six weeks an almost uniform layer of sand, 



