EARTHWORMS AND THE SOIL.—Darwin has explained the enormous effects which these soft-bodied and small creatures have had upon the superficial structure of the earth. Their castings, brought up to the surface, are blown about by the wind when dry, and are thus spread over the ground in a fine layer. It has been calculated that in the space of an acre .2 of an inch in thickness of earth is annually brought to the surface. It is clear therefore that in a long period of years there would be a very large effect produced. On the sides of a hill this matter brought up from below would tend to roll down the slopes when dry, and would increase the débris carried away to the sea by streams and rivers, so that continents formerly deposited under the sea may owe no small proportion of their size to the continued work of earthworms in past ages. Darwin has also pointed out the benefits to the agriculturist which accrue from the industry of these Annelids. The soil is thoroughly mixed and submitted to the action of the atmosphere. The secretions of the worms themselves cannot but have a good effect upon its fertility, while the burrows open up the deeper-lying layers to the rain. Mr. Alvan Millson,[421] in detailing the labours of the remarkable Yoruba worm (_Siphonogaster millsoni_ Beddard), hints that they may serve as a check upon the fatal malaria of the west coast of Africa. By their incessant burrowings and ejecting of the undigested remains of their food many poisonous germs may be brought up from below, where they flourish in the absence of sunlight and oxygen, and submitted to the purifying influence of sun and air.