THE ANATOMY OF THE MADEETOKAK1A. 9 



at the opposite ends of the long axis of the oval stomatodaeum, 

 thus differing from those of all other Hexactinise or Madre- 

 poraria yet described. The significance of this fact cannot, of 

 course, yet be understood, as nothing correspondingly abnormal 

 occurs in any other part of the polyp with which it might be 

 correlated. As, however, the mechanical or other function of 

 the directive mesenteries is itself not yet explained, the mean- 

 ing of the variation from the common type is naturally not 

 appreciable. The number of the pairs of mesenteries, like that 

 of the septa, is not necessarily a multiple of six. 



The only point in the histology that appears worthy of note 

 is the great length of the calicoblasts, as compared with that 

 of the other cell-elements. A group of them from the edge of 

 a growing septum is represented in fig. 7. Still more marked 

 is the great length of these cells in fig. 8, which represents a 

 transverse section through the tissues at that point where the 

 upward growth of the theca divides the mesenteries into a cen- 

 tral portion within the calyx, and a peripheral portion outside 

 of it. Here they measure as much as 054 mm. The large 

 plate of mesoglcea in the centre of the figure is merely that 

 which immediately overlies the lip of the calyx, and is cut in a 

 direction parallel to its flattened surfaces, while the section 

 passes nearly at a right angle to the other tissues. The point 

 here figured is such a "centre of calcification" in the theca as 

 has been already referred to ( vide p. 7). 



iii. Summary. — The most important facts thus obtained 

 are — 



1. The polyps agree with the normal Actinian type, except 

 for the absence of "directive mesenteries/' They 

 possess a well-developed "Rand-platte." 1 



2. The septa and tentacles are both ectoccelic and ento- 

 ccelic, the number of septa not being necessarily a multiple of 

 six. 



3. Three series of centres of calcification are recognisable in 

 the skeleton, of which one lies in the theca itself, and the 



1 It is, perhaps, unnecessary to coin an equivalent for this till its morpho- 

 logical value is better understood. 



