38 THE VOYAGE OF H.M.S. CHALLENGER. 



Spheroidal cavities occur excavated in the ccenosteum at a very slight depth from the 

 surface. These contain the gonophores in the recent state of the coral, and may be 

 called ampullae. They are in this genus entirely buried beneath the surface, whereas in 

 most genera of Stylasteridse they project above it often to a very conspicuous extent. 

 They communicate with the exterior when mature by means of small slit-like apertures 

 placed at the bottoms of small irregularly shaped depressions which are to be seen with 

 some difficulty scattered over the coral surface (PL II. fig. 2, GG). Only male specimens 

 of Sporadopora have been obtained as yet. No doubt, in the case of ampullae containing 

 female gonophores, a comparatively wide opening in the surface of the ccenosteum is formed 

 to allow of the escape of the fully formed planula. 



This actual tissue of the ccenosteum must be in Sporadopora and in most other 

 Stylasteridae excessively dense and compact, since the masses formed by it, although, as 

 described, excavated by canals in all directions, are heavy. 



In the older parts of the stems and their bases, the ccenosteum appears to become 

 compact and stony, and crystalline in fracture by obliteration of the canals and pores. 

 In some specimens, portions of the surfaces of the stems which have once been dead have 

 undergone rejuvenescence by the spreading of a thin layer of living coral over them from 

 adjacent healthy regions. 



The dead ccenostea are overgrown by a Flustra and other Bryozoa, and form bases of 

 attachment to large masses of other Stylasteridae, such as Errina labiata. 



Since the calcareous meshwork is closer at the surface of the ccenosteum, its meshes 

 must necessarily become enlarged by reabsorption as growth proceeds. Cavities also 

 such as those of the ampullae must be filled up as the ccenosteum grows. The irregular 

 cavities existing beneath the ampullae in some cases, as shown in Plate XXXV. fig. 1, 

 probably represent spaces occupied in an earlier condition of the coral by gonophores. 

 Sometimes also old ampullar cavities remain unfilled up, situate beneath the more super- 

 ficial and active ones. 



The tissue of the ccenosteum is very like that of Millepora in histological structure, but 

 appears somewhat more granular in texture, and less fibro-crystalline than it. 



Soft structures of Sporadopora dichotoma (PL III.). 



Cosnosarc. — The tortuous canals and pores by which the ccenostea of all the Stylasteridae 

 are traversed, are occupied in all the genera alike, in the living condition of the coral, by 

 a series of meshvvorks of correspondingly branching, twisting, and anastomosing canals, 

 which compose the coenosarc or common body of the compound organism in each case. 

 In Sporadopora only a comparatively thin layer on the surface of the coral is occupied 

 by living soft structures. These living structures are separated from the non-living- 

 deeper masses of the ccenosteum by the action of acids, and then appear as a sheet of soft 



