200 J. E. DugrpEN—Jamaican Actiniaria : 
are rather narrow and deep, but the presence of numerous sponge spicules 
interferes with a detailed study. As noticed amongst the external characters 
the polyps are capable of excessive retraction, so much so as to obliterate a 
great part of the ccelenteric space, and produce a great displacement of the disc 
and stomodeeal walls. 
The ectoderm of the tentacles presents throughout its extent a peripheral 
layer of small, narrow nematocysts, differing from the oval form in the column- 
wall. Below this nematocyst layer a nuclear zone is usually separable from 
the more internal nervous and muscular elements. An ectodermal and an endo- 
dermal musculature are developed; the former much the stronger. The layer of 
nerve fibrils is often distinguishable in connexion with the ectoderm. ‘The 
mesogleea is very thin, but a little better developed proximally ; it is finely plaited 
for the support of the ectodermal musculature. 
The endoderm contains zooxanthelle, and very often fine pigment granules ; 
these latter are also found in the ectoderm. Spicules occur in some abundance 
in the tentacular tissues, somewhat more numerous in the outer than in the 
inner cycle. Though such a position for inclusions is exceptional they are 
met with in all the examples studied, and in such a manner as to leave little 
doubt that they are not the result of displacement during the preparation of the 
sections. j 
The dise is very thin, and peripherally closely resembles the tentacles in 
structure; afew nematocysts occur in the ectoderm, as well as numerous 
deeply-staining granular gland cells. 
The vertical height of the stomodzum is remarkably small in contracted 
specimens (Pl. x1v., fig. 4); and in a series of transverse sections the sulcar end 
terminates in advance of the suleular. The single gonidial groove is clearly 
indicated. In transverse sections the wall is usually cut through twice as 
a consequence of the partial reflection of the internal termination of the stomo- 
deum. As seen in the figure, the stomodzal wall passes slightly upwards and 
outwards for a considerable distance. ‘The ectoderm displays the usual histo- 
logical structure, consisting mainly of ciliated supporting cells, the combined 
nuclei of which give rise to a very distinct zone; granular gland cells, which also 
stain deeply, are abundant, especially in the upper regions, but nematocysts do 
not appear to be developed. No ectodermal musculature is discernible over any 
part of the stomodeum. The mesoglcea is very thin, and undergoes no appreci- 
able thickening at the groove. In vertical sections the stomodeal ectoderm 
is In continuity with the mesenterial filaments; but there is no special forma- 
tion of reflected ectoderm. 
Owing to the extreme retraction and the shortness of the stomodzeum, some 
difficulty is experienced in making out the arrangement of the mesenteries; but 
