262 Mr. H. J. Carter on the 



where the general structure is similar, i. e. composed of a 

 branched anastomosing tubulation in which the latter is one 

 third of an inch in diameter, and thus forms a clathrous 

 mass. (By " calcareous " I mean charged with globular 

 spined spicules of carbonate of lime, like those of the Dide- 

 mida, Giard.) Now all these are built upon the same design, 

 and in all the oral orifices of the organisms respectively pro- 

 ducing them are on the outer side of the tubulation ; yet no 

 naturalist would assert that a polyzoon, a spongozoon, and 

 an ascidian were one and the same organism. Hence the 

 form may be the same, but the function different ; and so the 

 stellate venation of Stromatopora may be like the stellate ex- 

 cretory canal-system of sponges presenting this form, with a 

 totally different function ; on the other hand, in Hydractinia 

 and Stromatopora respectively, the form of the venation may 

 be different and the function the same. 



Lastly, we come to the " vertical rods " of Stromatopora, 

 to which I have alluded as always existing in the rectilinear 

 and only sometimes in the curvilinear ccenenchyma, pre- 

 senting an axial transparency indicative of their having once 

 been hollow in the whole of their length, except probably at 

 the surface, where the hollow is closed ; and that this was 

 probably the case we arrive at in the following way, viz. 

 that the spines in both Hydractinia echinata and H. calcarea 

 which pass up through the whole layer of the polypary are 

 respectively hollow throughout, but closed at the apex (Ann. 

 1877, vol. xix. pi. viii. figs. 1 and 4) — also that the spines 

 on the surface of the fossil species, viz. H. pliocena, are the 

 same, and appear to be continuous with the vertical tubes 

 in the stroma or corallum, while Labechia conferta of the 

 Silurian Formation (which was a species of Hydractinia, and 

 to which I shall allude more particularly hereafter) presents 

 the same kind of axial transparency in its vertical rods or 

 columns, which terminate in opaque (closed) conical points 

 respectively on the surface, indicative of their also having 

 been in like manner otherwise hollow (fig. 8, a, b). Hence 

 too, perhaps, Ave may account for the axial transparencv, 

 indicating original hollowness, in the " vertical rods " of 

 Stromatopora. 



Further, if we compare Favosites gothlandicus (fig. 7) with 

 Labechia conferta (fig. 8 — both fossils of the Silurian Forma- 

 tion), both will be found to be composed of vertical spaces 

 tabulated ; but while the former was composed of tubes in 

 juxtaposition with horizontal tabula? (fig. 7, b), the latter was 

 composed of thick hollow columns between which the tabula? 

 were extended in a much less regular manner (fig. 8, a, b) ; 



