IN 7 



PHYLUM CCELENTERATA 



185 



the ccenosarc or, as in Pennatula itself, from flattened lateral 

 branches. 



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

 Coral (Tubipora): The base of the original 

 polype (Fig. 135) grows out into a flattened 

 expansion from which new polypes arise, 

 diverging slightly from one another as they 

 grow, and separated by tolerably wide inter- 

 vals. The distal ends of the polypes then 

 grow out into horizontal expansions or plat- 

 forms (pi.), formed at first of ectoderm and 

 mesoglcea only, but finally receiving prolonga- 

 tions of the endoderm. The platforms extend, 

 come in contact with one another, and fuse. 

 In this way platforms of considerable ex- 

 tent 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 passu with the vertical growth of the 



FIG. 132. Corallium 

 rubrum, portion 

 of a branch. (After 

 Claus.) 



FIG. 133. Astrsea pallida, the living colony. (After Dana.) 



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 

 is the arrangement of the mesenteries. In Edwardsia (Fig. 136), 

 a genus which burrows in sand, instead of attaching itself to 



