Today is Charles Darwin's 200th birthday. (Bows head in reverence.)
Towards the end of his long and amazing life, Darwin was finally able to devote himself to a lifelong interest- the biology and function of earthworms. While still in his thirties, he was certain that earthworms performed a key role in soil biology, though he was unable to spend time on what he called his "hobbyhorse" until old age. His last volume is still considered one of the best studies ever written on earthworms, called "The Formation of Vegetable Mould, Through the Action of Worms, With Observations of their Habits". It was published in 1881, one year before his death. The entire book is available on-line here.