214 Mr Harmer, On Cyclostomatous Polyzoa. [Oct. 26, 



one another. In other words, the two free ends of the interrupted 

 terminal membrane grow towards one another above the proximal 

 end of the colony. When they have united, complete fusion takes 

 place, and the two halves of the membrane become completely 

 confluent. This results in the assumption of a secondarily discoidal 

 condition, which differs fundamentally in origin from the discoidal 

 colony of Lichenopora, where the entire rim of the colony is a 

 direct derivative of the rim of the young funnel-shaped stage. 



In Grisia again, the branching colony is produced by the 

 repeated division of the terminal membrane, accompanied by great 

 elongation of the lobes or branches to which the growing-points, 

 or segments of the terminal membrane, give rise. The branches 

 at the same time become jointed. In other words, a Crisia-colony 

 is comparable with a funnel whose distal end has become repeatedly 

 divided in a longitudinal direction, the divisions extending a 

 varying distance towards the base of the colony. The basal lamina 

 of Lichenopora and Idmonea is thus represented by the "backs" of 

 the branches. 



The above instances will serve to show that the zoarial form of 

 several types of apparently dissimilar Cyclostomes is regulated by 

 a law of growth which is probably common to the majority of 

 recent species, if not to all. The unilaminate condition of Hornera, 

 of Frondipora verrucosa, and of erect species of Idmonea is readily 

 intelligible on the supposition that the " backs " of the branches 

 correspond with the basal lamina of encrusting species. 



