work on this question affords a striking example of the
tenacity of purpose with which he continued his enquiries on any subject
that interested him.

In 1842, as soon as he was settled at Down, he began a series of
observations on a foot-path and in his fields, that continued with
intermissions during his whole life, and he extended his enquiries from
time to time to the neighbouring parks of Knole and Holwood. In 1844
we find him making a communication to the "Gardener's Chronicle" on the
subject. About 1870, his attention to the question was stimulated by the
circumstance that his niece (Miss L. Wedgwood) undertook to collect and
weigh the worm-casts thrown up, during a whole year, on measured
squares selected for the purpose, at Leith Hill Place. He also obtained
information from Professor Ramsay concerning observations made by him on
a pavement near his house in 1871. Darwin at this time began to realise
the great importance of the action of worms to the archaeologist. At
an earlier date he appears to have obtained some information concerning
articles found buried on the battle-field of Shrewsbury, and the old
Roman town of Uriconium, near his early home; between 1871 and 1878 Mr
(afterwards Lord) Farrer carried on a series of investigations at the
Roman Villa discovered on his land at Abinger; Darwin's son William
examined for his father the evidence at Beaulieu Abbey, Brading,
Stonehenge and other localities in the neighbourhood of his home; his
sons Francis and Horace were enlisted to make similar enquiries at
Chideock and Silchester; while Francis Galton contributed facts noticed
in his walks in Hyde Park. By correspondence with Fritz Muller and Dr
Ernst, Darwin obtained information concerning the worm-casts found in
South America; from Dr Kreft those of Australia; and from Mr Scott
and Dr (afterwards Sir George) King, those of India; the last-named
correspondent also supplied him with much valuable information obtained
in the South of Europe. Help too was obtained from the memoirs on
Earthworms published by Perrier in 1874 and van Hensen in 1877, while
Professor Ray Lankester supplied important facts with regard to their
anatomy.

When therefore the series of interesting monographs on plant-life had
been completed, Darwin set to work in bringing the information that he
had gradually accumulated during forty-four years to bear on the subject
of his early paper. He also utilised the skill and ingenuity he had