MR. H. N. MOSELEY ON THE STRUCTURE OF THE STYLASTERTM. 435 
(Plate 36, N N). The nematopliores are irregularly semicircular in vertical section, with 
the flat side of the semicircle coinciding with the surface of the superficial layer of the 
ectoderm. Except on this flat side they are bounded by a membranous wall, which 
forms a sac open above. The open mouth of the sac is crammed with nematocysts of 
the larger kind, closely packed side by side, with their pointed ends directed to the 
surface. The cells are so closely packed that, in a section of the superficial layer 
taken parallel to the* surface through the nematopliores, no interstices can be seen 
between them (Plate 43, fig. 3, N). The lower part of the cavity of the nematophore 
is filled with nuclei and parent cells of the nematocysts. The nematopliores, as 
viewed from the surface of the superficial layer, are seen to have an irregular outline, 
showing a tendency to lie somewhat oblong, with curved boundaries. 
No triple-spined nematocysts, such as those occurring in Millepora and in most 
other Hydroids, were detected as existing in any of the Stylasteridee. The two 
kinds described as occurring in Sporadopora dichotoma appear to be present in all 
members of the family, with very slight variations in form indeed. 
Zooids. — The zooids in Sporadopora dichotoma are of two kinds, dactylozooids and 
gastrozooids : the former occupying the smaller, and the latter the larger, style-bearing 
pores, already described as characteristic of the corallum. 
Dactylozooids. — I have named the mouthless zooids of the Stylasteridse “ dactylo- 
zooids ” because, although they are invariably destitute of tentacles, they are reduced to 
the condition of simple tentacles themselves, and evidently perform a tentacular function. 
The dactylozooids are closely similar in form and structure in all the genera of 
Stylasteridse hitherto examined, and differ only in dimensions. They are simple, 
elongate, conical bodies, just like the ordinary tentacles of Hexactinians in form, and 
are devoid of mouth or any opening to the exterior. They are attached to, and, when 
unprotruded, retracted within membranous sacs or sheaths, which rest within the 
corresponding pores of the corallum. In Sporadopora, the sacs of the zooids, the 
walls of which are shown in longitudinal section in Plate 36, EE, are composed of a 
transparent membrane, derived from the ectoderm, and continuous with its surface 
layer. The membrane has numerous fine nuclei dispersed in its substance, and is 
strong and tough. It is lined on its inner surface next the cavity of the sac by 
a layer of small transparent cells, which are shown in the figure cited above. 
On their outer surfaces, the walls of the zooid sacs are abutted on by the peculiar 
radial offsets of the coenosarcal meshwork already described. These offsets appear to 
lose their tubular character as they near the walls of the sacs, and, as far as was seen, 
no openings occur in the sac walls communicating by means of these radial canals with 
the coenosarcal circulation, although such an arrangement was supposed to exist when 
the first hasty examination of specimens was made. 
The sacs are attached to the bases of the zooids, being continuous in those regions 
with the ectodermal covering of the zooids. They closely invest the retracted zooids, 
and are thus cylindrical in form in their deeper parts ; whilst above the level of the 
