The last subject Darwin is writing a book on is the worm. It seems symbolic. In 1881, when he is 72 years old, it is published under the title: The formation of vegetable mould, through the action of worms. It is fascinating to read. It describes among other things the way in which worms pull leaflets into their little holes. According to Darwin the worms show, doing this, a remarkable intelligence. They know exactly how to grab a leaflet. He has done experiments with this and he also enlisted his children in his research. In the morning there are always little piles lying on the entrances of the holes. In this way worms have an important function in the circulation of the mould layer.

Darwin has also demonstrated that stone objects slowly sink into the soil as a consequence of the activities of the worms. He could e.g. prove this on Roman foundations, which were sunk deep into the soil. To measure the rate of sinking, he had instructed to make a design of a Wormstone (see both pictures). In the middle was a pin resting on the solid sub-soil. In this way he could do his measurements.

Darwin 57

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