Hermit crab wood and stone are used by some species). The tip of the hermit crab's abdomen is adapted to clasp strongly onto the columella of the snail shell. Most hermit crabs are nocturnal. Hermit crabs can be divided into two groups: As hermit crabs grow, they require larger shells. Since suitable intact gastropod shells are sometimes a limited resource, vigorous competition often occurs among hermit crabs for shells. The availability of empty shells at any given place depends on the relative abundance of gastropods and hermit crabs, matched for size. An equally important issue is the population of organisms that prey
On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection paper, consisting of the letter and papers, was published in the "Zoological Journal of the Linnean Society 3" (20 August): 46–50. The paper consisted of a communication letter by Joseph Dalton Hooker and Charles Lyell dated 30 June 1859, giving information on the three sections of the papers. The introduction is shown below, along with the section headings: MY DEAR SIR,—The accompanying papers, which we have the honour of communicating to the Linnean Society, and which all related to the same subject, viz. the Laws which affect the Production of Varieties, Races, and Species, contain the results of the investigations