152 Happon anp DurrpEN—Some Actiniaria from Australia and other Districts. 
Body-wall (Pl. vut., fig. 9).—The ectoderm is regular in structure. In 
some places it is considerably folded, but some of this is probably due to unequal 
contraction. The contents of the columnar cells do not stain deeply. The small 
nuclei appear in sections more as a band towards the inner end of the cells. The 
diffuse ectodermal muscle layer is clearly seen. 
The mesogleea in the upper part is thicker than the ectoderm, but it thins 
considerably towards the base of the column. In some cases it follows the 
folding of the ectoderm. It is almost homogeneous in structure, but a few 
small elongated cells may be observed. 
The endoderm is a little thinner than the ectoderm, and is not thrown into 
ridges between any of the mesenteries. Highly refractive, club-shaped, glandular 
cells are present. A diffuse muscle is developed; towards the capitular region, it 
forms the endodermal sphincter muscle. 
Sphincter muscle (Pl. vi., fig.10).—The mesoglea is thrown into slight folds 
in the region of the diffuse endodermal sphincter, which, except for the greater 
development of the muscle fibres, is scarcely distinguishable from the general 
endodermal muscle of the body-wall. 
Tentacles—The ectoderm of the tentacles consists mainly of columnar cells 
similar to those of the body-wall, but the contents stain more deeply. A few 
deeply-staining, large, oval nematocysts, with a spiral thread inside, occur. 
Towards the distal end, long, very narrow, yellowish nematocysts are abundant, 
and show a spiral thread. The highly refractive glandular cells of the endoderm 
also occur in the more proximal parts. The ectodermal muscular layer is well 
developed. The mesogloea is much folded. The endoderm is about the same 
thickness as that of the column, and has also numerous glandular cells; a slight 
endodermal muscle occurs. 
Disc.—The dise is much like the body-wall in structure; large oval nema- 
tocysts occur, and glandular cells are present in both ectoderm and endo- 
derm. 
@sophagus.—The ectoderm of the cesophagus is much folded, and stains more 
deeply than that of the column; large oval nematocysts are present. The 
mesogloea is thin, and follows the folds of the ectoderm. An cesophageal groove 
is not distinct. 
Mesenteries.—The mesenteries consist of numerous pairs without, however, any 
apparent regular arrangement. Some specimens show only one pair of directives, 
while another shows two pairs. The arrangement and number of the pairs of 
perfect and imperfect mesenteries on each side of these is irregular. 
The endoderm of the mesenteries is rather thick, and is made up of large 
columnar cells and numerous glandular cells. The retractor muscle is well 
developed, and the mesogloea is thrown into broad folds for its support. The 
