Relative Growth of the abdomen and the carapace of the Shore-CrabCarcinus maenas

Abstract

1. In regard to relative abdomen-breadth and relative carapace-breadth, the common shore-crab Carcinus maenas in both sexes exhibits a continuous change of proportions throughout life, from small animals of 2 mm. carapace-length to the largest obtainable (over 50 mm. carapace-length).2. The parts measured exhibit constant differential growth-ratios (growth-coefficients) relative to carapace-length taken as standard, over long periods of the life-history.3. The approximate growth-coefficients are as follows, relative to carapace-length:Carapace-breadth, 1·06. This appears to be constant throughout the range of size measured, with a possible decline to nearly unity at large sizes.Abdomen-breadth.Crabs unsexable externally (2–6 mm. carapace-length), 1·26.Females: early phase, 1·26; late phase, 1·42.Males: early phase, 1·07; late phase, 0·94.The early phase begins as soon as the sexes can be distinguished. The onset of the late phase may be presumed to be correlated with sexual maturity. In females it occurs certainly between 17 and 20 mm. carapace-length, in males between 14 and 29 mm.4. There are indications of seasonal and local differences in relative abdomen size.5. Feeding crabs of 9 to 22 mm. carapace-length solely on fresh ox-thyroid or fresh ox-pituitary for periods up to a year produces no change in growth-rate or in secondary sexual characters as against controls fed on fresh fish.