THE STRUOTtJRE AND RELATIONS OP TQBIPORA. 559 



to observe), nor the pieces offered for sale by the dealers 

 possess the stolon at all. The stolon does not follow all the 

 fluctuations of its support, but in many places may be seen 

 to skip over large crevices. This point is, I think, of some 

 importance when we compare the stolon of Tubipora with 

 the creeping network of tubes from which the corallites of 

 Syringopora spring, the two being, I consider, homologous. 

 That the stolon should cease to grow at an early stage in the 

 growth of the colony is not to be wondered at, as its function 

 (namely, that of giving origin to new corallites) is completely 

 taken up by the platforms situated in the more peripheral 

 regions of the colony. 



The individual corallites then, originating either from the 

 stolon or from a platform, pass up through a varying num- 

 ber of platforms towards the periphery. They are usually 

 straight, but occasionally I have observed them deviating 

 considerably in their course. Their power of growth is not 

 unlimited ; in one case I have traced a single corallite passing 

 through as many as seventeen platforms, but the average number 

 does not exceed twelve or thirteen in Tubipora musica. 

 Towards the termination of the corallites the walls become 

 thin, lose their deep red colour, and end in pale jagged edges. 

 In the course of the growth of the colony these free ends of the 

 dead corallites become covered over by neighbouring platforms, 

 and lost to view. 



The platforms are formed as outgrowths from the lips of the 

 growing corallites, in a manner which will be more fully de- 

 scribed when I come to describe the soft parts of the animal. At 

 first they are exceedingly thin, and their skeleton composed only 

 of a few scattered spicules in the mesoderm. Consequently 

 in dried specimens the young platforms are entirely lost. 



As the platform becomes older it increases in thickness, and 

 the spicules unite together to form a firm lamina. E;ich of 

 these older platforms may be seen in section to be really com- 

 posed of two delicate lamina?, between which numerous canals 

 ramify in all directions (fig. 2). 



Some of the most important and interesting structures in the 



