Patterns of tube construction in the upright tubes of Rhabdopleura compacta are described. Tube building is seen to be a highly regular process, with growth extending over more than one season. Participation in the building of any one tube can involve multiple generations of zooids. Spatial awareness in a zooid adding new material to a pre-existing tube can be demonstrated. This shows that the construction of the tube is strictly determined, either by environmental or genetic mechanisms, rather than being a function of developing zooid morphology, as previously suggested, or random processes.