Size Variations in the Cyprids of Some Common Barnacles

The sizes, length and breadth, of the cyprids of Balanus balanoides , B. crenatus and Verruca stroemia have been measured on material collected. during the spring outburst and in the later part of the year. The size-frequency curves for Balanus balanoides and B. crenatus show at least two distinct modesduring the spring, equivalent to populations of two distinct sizes. It is suggested that these correspond to populations developed in different environments. Measurements of the nauplii taken from adults at different points on the shore indicate that the size of the nauplii is dependent to some extent upon the conditions of development, the conditions also affecting growth and total nauplii output. Swedish samples, in which the parents had developed under more uniform conditions, showed only a single population as regards size. In B. crenatus and Verruca stroemia , which produce further broods during the year, the size decreases in these later broods. The rate of development of the eggs and embryos, probably dependent upon temperature, is suggested as the important factor.