GENUS TINOPORUS. 227 



subdivided at its margin as to resemble the body of a Star-fish (figs. 7, 9), the areolar division 

 being continued nearly to the extremity of each ray, and its point only being formed by the 

 furrowed prolongation. These appendages are usually from four to six in number ; I have occa- 

 sionally seen only two, and in no case have I met with more than eight. They usually diverge in 

 or near the equatorial plane; but they sometimes come off in very different directions (fig. 8). 



397. Internal Strudare. — The general organization of T. baculatiis, brought into view 

 by sections taken in different directions, does not differ in any essential respect from that of 

 T. vesicularis ; the origin of the whole aggregation of chambers in a central cell, their subse- 

 quent multiplication both horizontally and vertically, and their methods of communication in 

 both directions, being all the same. As already mentioned, I have very distinct evidence, in 

 sections of this species, of a spiral commencement (fig. 1 1 a), soon giving place to an irregu- 

 larly- cyclical growth {b, h) ; and it is remarkable that the first-formed portion sometimes bears 

 so close a resemblance to the innermost part of the spire of Calcarina, that in this earliest 

 stage of their growth the two types could not be distinguished from each other. The essential 

 difference between T. haculatus and T. vesicularis consists in the possession by the former of 

 a " supplemental skeleton," which presents itself under two principal aspects. The piles of 

 chambers extending vertically from the equatorial plane towards the two surfaces of the 

 spheroid are partially separated by the interposition of pillars of solid shell ; and it is by the 

 projection of the summits of these pillars (as in Calcarina) that the tubercles of the surface 

 (fig. 5) are formed. The spines also, which form the extremities of the radiating prolonga- 

 tions, belong to the same system ; and they are shown, by sections that pass in a favorable 

 direction (fig. 12), to be extended from a solid framework which begins to be formed even 

 with the first convolution, and which adds greatly to the thickness of the partitions between 

 the chambers, giving off a multitude of minute spines from their external surface. This 

 framework is penetrated by a canal-system, which not only forms passages through the solid 

 axis that is prolonged into the spines (fig. 10, -', b), but also extends itself into the partitions 

 between the chambers (fig. 10, a, a). The canal-system of the solid axis, moreover, commu- 

 nicates freely with the cavities of the chambers that are adjacent to it, as is shown at fig. 10, b, b. 

 These chambers are arranged around it with considerable regularity, as is seen in fig. 11, 

 which is a transverse section of the base of one of the radiating prolongations, showing the 

 sohd axis with its radiating canals, surrounded by three rows of chambers. It would seem 

 as if, in the Polynesian variety of T. baculatus, the material of the supplemental skeleton were 

 appropriated rather to the formation of the solid pillars than to that of a solid axis for the 

 radiating prolongations ; the latter being much less conspicuous than it is in the Philippine 

 specimens, and sometimes appearing to be deficient altogether at their extremities. On 

 account of the variability of these differences, however, I cannot regard them as of any essen- 

 tial value. 



398. If any further evidence had been required as to the essential relation between 

 the " canal-system" and the " supplemental skeleton," I think that it must be satisfactorily 

 furnished by the comparison of the two species of Tinojjoriis now described. For in T. vesi- 

 cularis it is obvious that the system of communications which exists between its chambers is 

 adequate for all the ordinary wants of an organism of this type, the structure of which ia 



