MR. H. N. MOSELEY ON THE STRUCTURE OF THE STYLASTERID/E. 
453 
gastrozooids at their margins, but not from their under surfaces. Some of these large 
canals turn almost immediately after springing from the gastrozooids upwards, through 
the wall of the zooid system, to join the main network already described as communi- 
cating with the dactylozooids. The remainder of the large canals form a tortuous 
reticulation, which passes down through the ccenenchym of the corallum, by the side of 
the immediately adjoining zooid system, to anastomose with the corresponding 
reticulation arising 1 from the base of the gastrozooid of this latter. The walls of the 
ampullae, as shown in the figure, are traversed by a fine reticulation of the coenosarcal 
canals beneath their covering derived from the superficial layer of ectoderm. 
Nematophores, composed of nematocysts of the usual larger form, are placed on the 
pseudosepta, between the dactylozooids (Plate 40, N N). 
Zooids. — One form of dactylozooid and one of gastrozooid only is present. 
Dactylozooids. — These, in the retracted condition, are short cylindrical bodies, with 
a rounded, blunt -conical, free extremity. They widen out towards their attached 
extremities, and are united to the sides of the clactylopores which are outermost in 
the systems, and to their styles, by elongate bases, which are drawn out below into 
narrow prolongations which join the coenosarcal mesh work. The zooids are, in fact, 
attached in an almost precisely similar manner to that in which the dactylozooids of 
Spinipora echinata are fixed within their groove-like pores. The free cylindrical por- 
tions of the dactylozooids in the present species are bent upwards, so as to extend in 
the wide upper cavity of the dactylopore, in a direction parallel to that of the axis of 
the gastropore. They are seen thus projecting in the centrally placed zooid system 
represented on Plate 40, D Z, showing partly free above the inner margin of the 
dactylopore sac, partly seen through the transparent sac of the gastrozooid. A curved 
line, crossing them transversely, marks the point where the sac of the gastrozooid 
becomes bent over, and unites with that of the dactylozooid. The dactylozooid sur- 
faces, as well as those of the tentacles of the gastrozooids, are thickly set with 
nematocysts of the usual smaller form. 
Gastrozooids. — These are short and broad cylindrical bodies, somewhat contracted in 
diameter towards the middle of their length. They terminate above in a dome-like 
hypostome with the mouth opening at its apex, and are provided with a single whorl 
of light tentacles set on immediately below the hypostome. The tentacles are, in the 
contracted condition, very short and stout, with swollen, rounded knob-like extremi- 
ties, which reach to a height only just exceeding that of the summit of the hypostome. 
At the margins of their bases the gastrozooids (Plate 40, G G) are drawn out into a 
series of large radially-disposed canals, which lead directly into the cavities of the 
zooids, and the further disposition of which has been already described. The imme- 
diate under surface of the gastrozooids is devoid of canal offsets, and is attached to the 
centrally placed style. 
The histological structure of the zooids in the present species of Stylaster closely 
corresponds with that already described as existing in those of Sporadopova dichotoma. 
