114 ZOOLOGY 



discussed the evolution of man in general, and set forth 

 the supplementary theory of sexual selection. In 1872 

 appeared The Expression of the Emotions in Man and 

 Animals, in which it was shown that corresponding 

 muscles existed, which in contraction expressed more or 

 less similar feelings. Thus a certain psychological con- 

 tinuity in evolution was established, corresponding with 

 a morphological one. Observations on his own children 

 in early infancy were included in this study. There was 

 also a series of important botanical works, concerned 

 with the structure and fertilization of orchids (1862), 

 insectivorous plants and the movements and habits of 

 climbing plants (1875), the effects of cross- and self- 

 fertilization (1876), different forms of flowers on plants 

 of the same species (1877), and the power of movement 

 in plants (1880). 



Earthworms The last book, published in 1881, was on The Forma- 

 tion of Vegetable Mould, through the Action of Worms. 

 Darwin had observed that objects left on the ground in 

 England disappeared after a period beneath the earth, 

 and seeking the cause, noted that earthworms were con- 

 tinually bringing soil to the surface as a 'result of their 

 feeding and burrowing operations. This turning over 

 of the soil is of great importance from an agricultural 

 point of view, and the extent to which it goes on was 

 proved by a long-time experiment in which the power 

 of worms to bury objects was thoroughly tested. 



Darwin died on April 19, 1882, and was buried in 

 Westminster Abbey, a few feet from the grave of Sir 

 Isaac Newton. 



References 



DARWIN, FRANCIS. Life and Letters of Charles Darwin. 1887. 



DARWIN, FRANCIS. More Letters of Charles Darwin. 1903. 



LITCHFIELD, HENRIETTA. Emma Darwin. A Century of Family Letters. 



I9IS- 

 POULTON, C. B. Charles Darwin and the Theory of Natural Selection. 1896. 



