Specialism and Detail
Darwin is usually thought of as a gentleman naturalist and a scientific generalist, as his work ranged across and drew together different fields of knowledge. But Darwin also made substantial contributions to specialist subjects and acquired technical expertise in geology, zoology, and botany. He greatly valued the detailed work of specialists and drew upon it extensively throughout his career. Narrow, technical discussion was often the starting point for some of Darwin’s most valuable and enduring contacts. His life-long friendship with Thomas Henry Huxley, for example, began with detailed correspondence about barnacles.
Letter 1514 — Darwin, C. R. to Huxley, T. H., 11 Apr 
Darwin offers to send zoologist T. H. Huxley Ascidia specimens from the Beagle voyage. He describes some of them. He hopes Huxley will review his book [Living Cirripedia, vol. 1] which has been published for a year with no notice taken of it, except briefly by Dana. He discusses Limulus-like larva–“I have become a man of one idea. – cirripedes morning & night.”
Letter 1480 — Darwin, C. R. to Huxley, T. H., 23 Apr 
Letter 1587 — Darwin, C. R. to Huxley, T. H., 2 Sept 
Darwin mentions that the second volume of Living Cirripedia is published. He asks Huxley’s advice on presentation copies for continental naturalists. He compliments Huxley’s review of Vestiges of creation in [Br. & Foreign Med.-Chir. Rev. 13 (1854)], but notes that he himself is almost as unorthodox on species as the author of Vestiges. He hopes he is not quite so unphilosophical. He hopes Agassiz was sounder on embryological stages than Huxley thinks.
Letter 1592 — Darwin, C. R. to Huxley, T. H., 13 Sept 
Letter 1635 — Darwin, C. R. to Huxley, T. H., 20 Feb [1855?]