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. Il. fig. 4). These channels correspond with those 
described as occurring in Hrrina, 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 frequently 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 
Spinipora echinata is hard and compact in structure, and white. 
Soft structures of Spinipora echinata (PI. V.). 
Cenosarc.—The ccenosare consists of the usual reticulation of canals (Pl. 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 coenosteum 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 canals 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 
