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



these smaller pores often have the sides of their mouths slightly raised above the 

 surface which they perforate. 



The main surface of the stems and branches of the ccenosteum is grooved, by short 

 canals, which are just open to the surface and run short courses, being never much 

 branched and usually crooked (PI. II. fig. 4). These channels correspond with those 

 described as occurring in Errina, and are occupied in the recent condition of the 

 coral by the most superficial reticulations of the ccenosarcal meshwork. 



Lying in deep depressions between the bases of the spinous projections are the 

 gastropores, which are deep pits with circular mouths, at the margins of which 

 dactylopores of the smaller kind frecmently open. The gastropores are provided with 

 styles, which are very deeply situate and have brush-like tips, and are much like those 

 of Sporadopora, but not so elaborately branched. The substance of the ccenosteum of 

 Spinipom echinata is hard and compact in structure, and white. 



Soft structures of Spinipora echinata (PI. V.). 



Coenosarc. — The ccenosarc consists of the usual reticulation of canals (PI. V.), offsets 

 of which pass into and ramify within the dactylopore spines as at B, Plate V. There 

 is a well-developed continuous surface layer of ectoderm which invests the spinous 

 processes and entire surface of the coral, and feebly maintains, in decalcified specimens, 

 the form of the ccenosteum. The layer is, as in other genera of the family, continued into 

 the pores of the ccenosteum to form the sacs of the zooids. The nematocysts are closely 

 similar to those of Errina. 



Dactylozooids. — These are of two forms, larger and smaller. The larger dactylozooids 

 are attached by elongate bases along nearly the whole lengths of the bottom of the 

 groove-like dactylopore cavities. The ends of these elongate bases nearest the coral 

 stems assume a cylindrical form, and are continued into the pore-like prolongations 

 of the grooves to become continuous with cauals of the ccenosarcal meshwork. In 

 Plate V. two dactylopore spines, B B, are shown as cut open in order to exhibit this 

 arrangement. The pore-like continuations of the dactylopore grooves are lined by 

 continuations of the surface layer representing the zooid sacs. The free parts of the 

 dactylozooids spring from the elongate attached parts not far from the tips of the 

 spines. In the contracted condition they appear as short, stout, bluntly-conical bodies, 

 which are slightly curved and bent inwards towards the coral stem, and at the same 

 time directed towards its upper extremity. Since the larger dactylozooids were all found 

 in the described condition in spirit specimens, it would appear that they are incapable of 

 being retracted to a greater extent, The pores are certainly not deep enough to allow 

 of their entire retraction within them, and the mode of attachment of the bases would 



