264 General Biology 



leaves are not, as a rule, drawn into the burrows, the heap of castings 

 serving the purpose. 



"The burrow is made partly by the awl-like, tapering anterior end 

 pushing aside the earth on all sides, and partly by the actual swallowing 

 of the earth as the worm advances, so that the animal literally eats its 

 way into the soil. The organic material in the swallowed soil serves 

 as food, and the residue in a state of very fine division passes out at the 

 anus, and is used either to form the above mentioned castings or as a 

 lining to the burrow, especially where this passes through hard, coarse 

 earth. 



"Perfectly healthy worms seldom leave their burrows completely 

 except perhaps after a very heavy rain. The majority of those so fre- 

 quently found traveling over the surface of roads and paths after rain 

 are infected by the larvae of parasitic flies and doomed to die. On warm, 

 moist evenings, however, worms may be seen in hundreds lying stretched 

 on the surface of the ground with only the broad flattened posterior end 

 remaining in the burrow. Here we see one of the uses of this modifica- 

 tion in the shape of the hinder segments of the body : their greater width 

 enables them to obtain a firm purchase on both sides of the burrow, and 

 thus the worm is provided with a sure anchor on which it can pull, and 

 at the slightest alarm, shoot back like stretched elastic into the security 

 of its burrow. At other times the flat tail is employed trowelwise in 

 smoothing the excrement against the walls of the burrow or in disposing 

 the castings on this side and on that of the mouth of the burrow. 



"The effects produced on the surface soil by the action of earth- 

 worms have been fully pointed out by Charles Darwin in his well-known 

 book, 'Vegetable Mould and Earthworms.' It will be sufficient here to 

 call attention to a few facts only. Worms play a most important part 

 in maintaining the soil in a state suitable to vegetation. The burrows 

 form ventilating tubes whereby the soil is aerated and respiration by the 

 roots of plants rendered possible ; at the same time they open up drain- 

 age channels, preventing the surface from becoming waterlogged. 

 Doubtless also roots find an easy passage through the soil along the 

 lines of burrows even after the walls have more or less fallen in. More- 

 over, the excrementitious earth with which the burrows are lined is 

 peculiarly suited to root fibers, being moist, loose and fertile. Micro- 

 scopic examination of the earth deposited by worms shows it to resemble 

 two-year-old leaf mould such as gardeners use for seed-pans and 

 pricking-out young seedlings ; most of the plant-cells are destroyed, 

 shreds and fragments alone remaining, discolored and friable, mingled 

 with sand grains and brown organic particles. In chemical composition, 

 too, worm-castings are very similar to fertile humus. 



"The castings which are thrown up on the surface materially im- 

 prove the quality of the upper soil, and render it more fit for the germi- 

 nation of seeds, many of which directly or indirectly get covered by the 

 upturned earth. It has been reckoned that there are upwards of 50,000 



