214 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



sunlight which is the most universal, effective, and economical of all 

 germicides. 



In Yorubaland, on the West Coast of Africa, Mr. Alvan Millson 

 calculated that about 62,233 tons of subsoil are brought every year 

 to the surface of each square mile, and that every particle of earth, to 

 the, depth of two feet, is brought to the surface once in twenty- seven 

 years. It need hardly be added that the district is fertile and healthy. 



Earthworms play their part hi the disintegration of rocks, letting 

 the solvent humus-acids of the soil down to the buried surface. Their 

 castings on the hill-slopes are carried down by wind and rain and go 

 to swell the alluvium of the distant valleys or the wasted treasures of 

 the sea. The well-known parallel ledges along the slopes of grass-clad 

 hills are partly due to earthworm castings caught on sheep-tracks, and 

 thus we begin to connect the earthworms not only with our wheat- 

 supply but with our scenery. Well may we say, with Darwin: "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 organised creatures." Those who wish to understand Darwin- 

 ism should always begin with Darwin's last book The Formation 

 of Vegetable Mould through the Action of Worms (1881). It illus- 

 trates the web of life, the idea of which is essential to an understanding 

 of the struggle for existence and natural selection. But it also illus- 

 trates what Darwin had learned from Lyell that great results may 

 be brought about by accumulation of infinitesimal items. As Professor 

 A. Milnes Marshall said: "The lesson to be derived from Darwin's 

 life and work cannot be better expressed than as the cumulative im- 

 portance of infinitely little things." 



Termites, or white ants. Henry Drummond, in his Tropical 

 Africa, tried to make out a case for the agricultural importance of 

 termites, or white ants. It is well known that these old-fashioned 

 insects have a pruning action in the forest, destroying dead wood with 

 great rapidity. Houses and furniture, fences and boxes, as well as 

 forest- trees, fall under their jaws. In some places, "if a man lay 

 down to sleep with a wooden leg, it would be a heap of sawdust in the 

 morning." But what of the termites' agricultural importance ? The 

 point is that they keep the soil circulating by constructing earthen 

 tunnels up the sides of trees and posts and by making huge obelisk-like 

 ant-hills, or termitaries. "The earth-tubes crumble to dust, which is 

 scattered by the wind; the rains lash the forests and soils with fury, 

 and wash off the loosened grains to swell the alluvium of a distant 



