Hydractinia, Parkeria, and Stromatopora. 59 



to the real nature of Parheria, viz. whether the " primordial 

 chamber-cone " of Dr. Carpenter is, or is not, a foreign body 

 and' not the natural nucleus of Parkeria, It is a foreign 

 body. Out of tlie sections of Parlceria that I have examined, 

 one of wliich is in my own poseession, by far the greater 

 number present a fragment of a concamerated test like that of 

 a minute Nautilus or Ammonite, in which more or less septa 

 are distinctly visible. Moreover the interior of the chambers 

 of the fragment is filled with transparent calcspar, the lamina 

 of white shell-substance surrounding it being still present and 

 contrasting strongly with the grey tissue-fibre of the Parkeria^ 

 which only begins to make its appearance outside the con- 

 camerated test, as the , homogeneity of the calcspar filling the 

 interior evidently demonstrates. The instance in my own 

 possession presents itself in a spherical specimen of Parkeria 

 I inch in diameter (fig. 17), where the foreign body consists of 

 a fragment of a nautiloid shell whose transverse section repre- 

 sents a hyperbola with its apex in the centre of the Parkeria^ 

 on which the structure of the latter has evidently commenced 

 growth (fig. 17, c). This hyperbola is 5-48ths inch high and 

 4-48tlis inch in diameter at the base, while the concavity of the 

 septum, of which only one is visible, is a little more than 

 4-48ths inch from the apex. The chamber thus formed be- 

 tween the septum and the apex of the hyperbola is filled with 

 calcspar ; and immediately outside the septum the reticulated 

 tissue-fibre of Parkeria. (fig. 17, V) is as distinctly visible as its 

 absence is distinct within the septum. 



After this, it may be stated that Parkeria is seldom without 

 some foreign body either about its centre or in some part of its 

 structure between this and the circumference, sometimes 

 singly, at others in plurality ; while sometimes it appears to 

 have grown round the extremity of a cylindrical body ~ inch 

 or more in diameter, and sometimes round a cylindrical body 

 of this kind which has traversed or transfixed it. But in most 

 of these instances the foreign bodies are made up of minute 

 Foraminifera, sponge-spicules, and fine material which looks 

 like part of a sea-bottom. How this is to be explained I am 

 ignorant. But the tissue-fibre itself is often filled up with 

 such material, wliich appears to have become incorporated 

 with it during growth. 



Lastly, we come to the natural surface of the full-grown 

 Parkeria, or to that of a specimen 1 1 inch in diameter ; and 

 this may be observed to be formed by the ends of the radiating 

 columns of tissue-fibre, which, at the circumference, rise above 

 the rest of the structure into little circular convex eminences, 

 varying in diameter under l-24th inch (fig. 16, o}, and possess- 



