Analysis of the Relative Growth of the Pacific Edible Crab, Cancer magister.

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Abstract
Summary: An analysis by the method of Huxley of approximately 4000 measurements made on about 1800 individuals of Cancer magister from the Pacific coast of North America is here presented. Slight heterogony has been found in the growth of the majority of its parts. In all aspects of relative growth it is extremely conservative. Changes in form indicate that sexual maturity in the female occurs at a carapace width of about 10 cm. This is confirmed by the size of ovigerous females and by observations of the development of the ovary. The sudden change in the length‐width proportions indicates that sexual maturity is usually attained by a single moult. The size at which male crabs become mature could not be inferred with certainty from the present data. After sexual maturity has been attained the legs of male crabs grow more rapidly than the body and the legs of females continue to grow less rapidly than the body. As a consequence the legs of mature males are longer than those of mature females of corresponding carapace width. A change in the ratio of length to width of the sixth abdominal segment of females has been noted at a carapace width of 7 cm. No other change is known to occur at this size. It is possible that this is a precocious change associated with the approaching sexual maturity. Crabs from south‐eastern Alaska, both male and female, were found to be a little shorter in proportion to their width than the corresponding Boundary Bay crabs. It has been pointed out that most organisms display some heterogony and that bizarre forms must exhibit it to a greater degree than more conservative forms. It has further been pointed out that a strong negative correlation seems to exist between the degree of heterogony and the maximum size of a species. Unfortunately no data justifying speculation upon the causal relationships are available. Cancer magister in all aspects of relative growth displays great conservatism; no high values for k were found for this large and abundant species.

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