434 MR, H. K MOSELEY OR THE STRUCTURE OF THE STYLASTERI DTE. 
striated in appearance as if composed of fine fibrillse, are constantly to be seen, but 
they seem to occur at altogether irregular intervals, and only towards the more super- 
ficially lying parts of the zooid sacs (Plate 43, fig. 3 ; Plate 36, A A). 
A continuous layer of ectodermal tissue extends over the outer surface of the coral. 
N o distinct cell structure was made out in this surface layer in Sporadopora, although 
such probably exists, as it was clearly seen in the case of the surface layer of Errina 
labiata. The layer bridges over the gaps in the superficial meshwork of the coeno- 
sarcal canals, and portions of it close in the mouths of the sacs of the zooids when the 
zooids are in the retracted state. Over the mouths of the sacs and radial canals of 
the retracted gastrozooids these special parts of the surface layer appear as discs of 
membrane, with very small apertures in their centres, and showing a radial fibrillation 
diverging from these central openings, which seems as if caused by contraction of the 
tissue in order to close the aperture. 
Embedded in the surface layer are numerous nematocysts of two kinds, larger and 
smaller. These are figured Plate 43, fig. 9. The larger nematocysts are of the form 
of cylinders,, very slightly bent. Their ends from which the threads are shot are 
bluntly pointed, whilst their opposite extremities are rounded. The thread at rest is 
coiled up spirally within the cell, in the usual manner (Plate 43, fig. 9, a). The 
emitted thread has an elongate enlargement upon it near the cell, which is beset with 
a spiral of spines (a'). The remainder of the thread is simple. These larger 
nematocysts have a length of about '0016 of an inch. 
The smaller kind of nematocysts are of an ovoid form, slightly flattened on one side, 
and, like the larger kind, more pointed in shape towards the end from which the 
thread emerges. They measure '00064 of an inch in length. They have a small 
bladder dike enlargement on their emitted threads, but it is, as far as was ascertained, 
devoid of spines. 
In both kinds of nematocysts the threads are shot out, not in a line with the length 
of the cell, but at a slight angle to this, and in continuation of the curves of the cells. 
Thread cells of almost exactly similar structure to these two occur in all the genera 
of Stylasteridse, the soft parts of which are described in the present paper. 
The nematocysts are developed in transparent cells of the ectoderm, which always 
contain a nucleus of finely granular appearance. The young nematocyst is seen 
developing within the cell with the nucleus lying beside it, and in proportion as the 
nematocyst increases in size and maturity, the nucleus diminishes in bulk (Plate 43, 
fig. 9, c, d, e). 
Nematocysts of both kinds are to be seen in abundance in all stages of development 
in the ectodermal cells of the more superficial regions of the coenosarcal meshwork. 
Both larger and smaller nematocysts are present in abundance, scattered in the super- 
ficial layer of the ectoderm. 
The larger form of nematocysts also occur in well differentiated nematophores, which 
occur disposed irregularly amongst the zooids in the superficial region of the coral 
