ANNULATA, SEGMENTED WORMS 41 



interfere with the course ,of the golf balls on the putting greens of 

 golf courses. To rid these greens of this annoyance they are sometimes 

 sprinkled with a lime-and-sulphur mixture or some other poison 

 that is harmless to grass. As soon as the liquid soaks into the ground 

 the worms begin to wriggle out of their unseen burrows so that they may 

 be picked up and destroyed. To illustrate the abundance of earth- 

 worms in the soil, the writer once collected, in this way, over one hun- 

 dred worms, big and little, from a square yard of green. This habit of 

 bringing the subsoil to the surface is most important to the growth of 

 vegetation, the burrows make the soil porous, thus allowing air and mois- 

 ture to penetrate the earth and making it easier for roots to work through 

 the soil, and the castings are constantly building up a finely divided 

 surface at the rate, according to Darwin, of about one-fifth of an inch 

 each year, so that in a generation a rocky field may have all of its 

 stones buried out of sight. The intestinal secretions mixed with these 

 castings are probably beneficial to the soil. 



FIG. 27. Medicinal leech, Hirudo medicinalis. X%. The larger sucker is at the 



. posterior end. 



Darwin remarks upon the fact that long before the plow was in- 

 vented, even in the form of a crooked stick, the earthworms were con- 

 tinually turning up the soil in this way. Although they may some- 

 times do some damage to young and tender plants, earthworms are 

 evidently of immense benefit to man. Certain laboratory experiments, 

 also, have shown them to be of undoubted benefit to plants. 



It is also said that earthworms may be and actually are used as 

 food, though they will probably never be popular among civilized 

 peoples. On the other hand they may occasionally be a source of 

 infection in certain diseases by burrowing in the carcasses of buried 

 animals and bringing the germs to the surface where they may infect 

 other animals. They are thought to convey the germs of gapes, a 

 disease of chicks caused by a small worm parasite. 



