198 



ZOOLOGY 



SECT. 



the coenosarc or, as in Pcnnatula itself, from flattened lateral 

 branches. The stem itself is the equivalent of a polype. 



A very peculiar mode of budding occurs in the Organ-pipe 

 Coral (Tubipora). The base of the original polype (Fig. 148) 



grows out into a flattened expansion 

 from which new polypes arise, diverg- 

 ing slightly from one another as 

 they grow, and separated by toler- 

 ably wide intervals. The distal ends 

 of the polypes then grow out into 

 horizontal expansions or platforms 

 (pL), formed at first of ectoderm and 

 mesogloea only, but finally receiving 

 prolongations of the endoderm. The 

 platforms extend, come in contact 

 with one another, and fuse. In this 

 way platfoims of considerable extent 

 are formed (A, pl.\ uniting the 

 polypes with one another. From 

 the upper surfaces of the platforms, 

 between the older polypes, new 

 buds arise, and in this way the colony tends to assume the form 

 of an inverted pyramid, the number of zooids, and consequently 

 the diameter of the colony, increasing pari 2Mssu with the vertical 



FIG. 145. Coralliuxn rubrum, por- 

 tion of a branch. (From Claus, 

 after Lacaze-Duthiers.) 



FIG. 146, Astrsea pallida, the living colony. (After Dana.) 



growth of the latter. The skeleton of this remarkable coral will 

 be referred to hereafter. 



Although the general structure of the individual polypes 

 of the Actinozoa is, as mentioned above, very uniform, the varia- 

 tions in detail are numerous and interesting, especially among 

 the Actiniaria. One of the most important points to consider 



