II. On certain correlated variations in Carcinus mænas

In previous communications I have discussed the variations in size occurring in one or two organs of the common shrimp (Crangon vulgaris). In these papers it has been shown (1) that the observed deviations from the average size of every organ measured are grouped symmetrically about the average, and occur with a frequency corresponding closely to that indicated by the probability integral; and (2) that the “degree of correlation” between a given pair of organs is approximately the same in each of five local races of the species (‘Roy. Soc. Proc.,’ vol. 47, p. 445, and vol. 51, p. 2). In what follows I shall describe the results obtained by measuring certain parts of the shore crab (Carcinus mænas) in two samples, one from the Bay of Naples, and one from Plymouth Sound, each sample consisting of 1,000 adult females.