Erratum.
In the report "A candidate magnetic sense organ in the yellowfin tuna, Thunnus albacares" by M. M. Walker et al. (18 May, p. 751), the standard error given on page 752 (3rd column, first full paragraph) for the sizes of the magnetite particles was instead the standard deviation. Use of the term "standard error" implies a far greater variance in the sizes of the particles than actually existed and could lead to the conclusion that the published electron micrograph is not typical but presents a biased sample of the particles.