1. The volumes of Balanus balanoides, at three levels of the shore, have been observed for a year.2. The young barnacles grow very much faster than older ones.3. The growth rate varies greatly with age, season and tidal level, but in general there is a period of maximum growth in the summer, and very little growth in the winter.4. Growth, except during the first year, is greatest higher up the shore.5. Young barnacles, which settle too late in the year, have their growth retarded by the summer heat, but almost catch up in size the earlier settled spat, by the beginning of the next year.6. The growth rates found are intermediate between those recorded from Herdla (near Bergen), and those from near St. Malo.7. Most of the lower- and middle-zone barnacles die in their third year, but those from the extreme top zone may live for five years or more.