ON THE DEVELOPMENT OP TUBULIPORA. 109 



from its base of support, these short ridges may grow out into 

 short foot-like columns of support. 



The lobes of this form of T. plumosa are ofteu narroW; 

 with nearly parallel radial sides. In well-grown colonies the 

 parallel sides of adjacent lobes are commonly in close proximity, 

 and they may then unite by means of these attaching pro- 

 cesses, which grow towards one another and fuse. This may 

 occur distally, but not proximally, so that narrow fenestrse 

 are left between the united lobes, and these are most easily 

 seen from the back of the colony. A colony whose lobes have 

 thus united may have an almost completely circular edge, and 

 may at first sight appear to have an undivided terminal mem- 

 brane. That this is not the case can usually be seen by careful 

 examination, and the original lobes are indicated not only by 

 continuing to develop their zocecia in alternate, connate series, 

 but also by a slight undulation of the growing edge, due to the 

 fact that the distal border of each lobe has a convexity which 

 has a shorter radius than that of the entire colony. Somewhat 

 similar colonies of this species growing on shells have been 

 described above (p. 99). 



I have not found these attaching ridges or processes on 

 specimens of this species growing on other seaweeds, nor have 

 I found them in any other species. It appears, therefore, 

 possible that the ridges are, from some cause, a special adapta- 

 tion connected with the occurrence of T. plumosa on this 

 particular seaweed. 



T. plumosa appears to be a shallow water form. Its 

 fondness for Saccorhiza bulbosa has been already referred 

 to. It is dredged at Plymouth in great numbers on Cysto- 

 seira granulata from a few fathoms depth. On this sea- 

 weed the colonies are small and irregular in their growth, 

 owing to the small diameter of the stems round which they 

 grow. I obtained numerous specimens, which were much 

 more convenient for examination, growing with T. phalangea 

 on Rhodymenia ciliata from the Salcombe Estuary. The 

 flat surfaces of this seaweed induce a regular growth in the 

 Tubulipora, which are thus well adapted for the preparation 



