Part IT.—Stichodactyline and Zoanthec. 151 
than any other form I have studied. ‘This is probably a result of the excessive 
abundance of glandular cells in both ectoderm and endoderm. The nuclei of 
the ectodermal cells of the column-wall become aggregated towards the mesoglea, 
and the muscular layer is distinctly recognizable where much shrinkage has not 
taken place. No nematocysts are present. 
The mesogleea is thin, but distally is formed into irregular plaits for the support 
of the endodermal muscle. On its ectodermal aspect it is thrown into the deep 
ridges with wide intervening furrows, already noticed among the external 
characters. 
The endoderm bears numerous zooxanthelle, especially above, and also 
scattered nematocysts. The cells are long and narrow, and the nucleiare arranged 
in a very narrow zone. ‘The endodermal musculature commences a little above 
the base as a very thin, smooth layer; distally, however, it is more developed on 
slightly branching mesoglceal plaitings, being most concentrated just below the 
marginal tentacles (Pl. x1., fig. 3). This exaggeration should probably be regarded 
as a diffuse endodermal sphincter muscle, continuous on the one hand with that of 
the column-wall, and on the other with that over the smooth naked portion of the 
dise. It is obvious that no very precise distinction can be drawn in the early 
stages of development between a strong endodermal muscle and a concentration 
which may be spoken of as a diffuse endodermal sphincter; and, even in the 
same species, there is undoubtedly much variation in the extent of the mesogleal 
foldings, according to the degree of retraction in which the polyp happened to be 
preserved. 
The musculature appears to be a little better developed than was found by 
Prof. M*Murrich in his Bahaman specimens. In these the circular muscle of the 
column is described as being throughout exceedingly feebly developed. The extent 
of development here given was met with in two examples sectionized; but in a 
third the concentration of the muscle fibres and folding of the mesogloea was 
observable to a much less degree, the condition evidently being about the same as 
that found by M*Murrich. The two first specimens were somewhat infolded in 
preservation, while the other was extended. 
Professor M*Murrich (p. 44) notes as a peculiar feature of the ectoderm of the 
disc, marginal tentacles, and disc tentacles that nematocysts are entirely absent. 
I have made a careful investigation of this exceptional condition, and, so far as 
regards the results obtainable from sections, my experience agrees with that of 
M*Murrich, but on submitting the marginal tentacles to maceration I find ecto- 
dermal nematocysts very abundant at the tips. They are elongated, rounded at 
each end, and the spiral thread is not very distinct, while the interior presents a 
granular appearance. The endoderm also contains many nematocysts, but they 
are of a totally different character. Maceration of the ectoderm of the dise 
Z2 
