f Chili he had found a curious
new cirripede, to understand the structure of which he had to examine
and dissect many of the common forms. The memoir, which was originally
designed to describe only his new type, gradually expanded into an
elaborate monograph on the Cirripedes (barnacles) as a whole group. For
eight years he continued this self-imposed task, getting at last so
weary of it as to feel at times as if the labor had been in some sense
wasted which he had spent over it; and this suspicion seems to have
remained with him in maturer years. But when at last the two bulky
volumes, of more than one thousand pages of text, with forty detailed
plates, made their appearance, they were hailed as an admirable
contribution to the knowledge of a comparatively little known department
of the animal kingdom. In the interests of science, perhaps, their chief
value is to be recognized, not so much in their own high merit, as in
the practical training which their preparation gave the author in
anatomical detail and classification. He spoke of it himself afterward
as a valuable discipline, and Professor Huxley truly affirms that the
influence of this discipline was visible in everything which he
afterward wrote.

It was after Darwin had got rid of his herculean labors over the
"Cirripede" book, that he began to settle down seriously to the great
work of his life--the investigation of the origin of the species, of
plants and animals. Briefly, it may be stated here that he seems to have
been first led to ponder over the question of the transmutation of
species, by facts that had come under his notice during the South
American part of the voyage in the Beagle--such as the discovery of the
fossil remains of huge animals akin to, but yet very distinct from, the
living armadillos of the same regions; the manner in which closely
allied animals were found to replace one another, as he followed them
over the continent; and the remarkable character of the flora and fauna
of the Galapagos Archipelago. "It was evident," he says, "that such
facts as these, as well as many others, could only be explained on the
supposition that species gradually become modified; and the subject
haunted me." His first note-book for the accumulation of facts bearing
on the question was opened in July, 1837, and from that date he
continued to gather them "on a wholesale scale, more especially with
respect to domesticated productions, by printed inquiries, by
co