A study of relative growth in UCA pugnax.

1. 50 males and 43 females were divided into classes according to carapace breadth. The relative growth rates of certain parts of the body were investigated by analysis of linear measurements carried out on the carapace and appendages. 2. The increased growth rate of pereiopods immediately posterior to the strongly heterogonic cheliped was concluded to be due, in part at all events, to the rapid growth of the cheliped, since the increase is considerably smaller on the small cheliped side in the male. 3. There seems to be, in addition, a sexual difference, the growth in the corresponding pereiopods in the female differing from that found in the male on the small cheliped side. 4. In the female the growth of the last two pereiopods is greater than that in the male; it is suggested that this is possibly due to the influence of the region of rapid growth present in the abdomen in the female. 5. The appendages anterior to the large cheliped in the male are apparently not inhibited. In this respect Uca pugnax differs from other forms which have been investigated. 6. The growth rate of the carapace breadth is greater than that of its length throughout the period investigated in the male, but only throughout the earlier part of the development of the female.