Part I1.—Stichodactyline and Zoanthee. 159 
As noticed among the external characters, the ectoderm of the column-wall is 
thrown into fine ridges and grooves. In section the former are shown to be sup- 
ported by comparatively long mesogloeal processes, which may even become 
branched (PI. x1., fig. 6). Numerous clear gland cells are present in the layer, along 
with fewer granular gland cells; many of the former are fixed with the mucus in the 
act of streaming out. A very distinct though weak ectodermal musculature is 
seen in transverse sections, more readily noticeable on the mesogloal processes. 
The mesoglcea is thin for its whole length, and becomes even more so towards 
the apex. The endodermal muscle is recognizable throughout the extent of the 
column as a feeble layer, but the fibres become a little stronger towards the 
apex, though no concentration which can be regarded as a special sphincter 
muscle takes place. The mesoglea is thrown into very slight folds for its support, 
and very fine fibrils pass from these towards the free surface of the endoderm, 
where the nuclei and zooxanthelle are mostly concentrated. The commensal algze 
are much more abundant in the distal regions of the polyps than proximally. 
The marginal and the disc tentacles display a similar structure. For the 
greater part of the length of the stem the ectoderm contains many gland cells, 
and its histology closely resembles that of the column-wall. ‘Towards the free 
termination an important modification take place ; the majority of the cells are no 
longer broad and glandular, but elongated, narrow, and closely aggregated, while 
deeply-staining nuclei are abundant. A peripheral zone is made up almost entirely 
of large elongated cnidocysts, witha fine spiral thread inside. In the deeper parts 
of the layer others are seen in different stages of development, and very distinct 
fibrillar and nervous layers occur just outside the ectodermal muscle. The ecto- 
dermal and endodermal musculature are both very feeble. 
Professor M°*Murrich (p. 48) found the tentacles in the Bahaman examples 
characterized by the total absence of nematocysts, a condition at variance with 
the Jamaican representatives, where both the marginal and disc tentacles are 
crowded with nematocysts around their extremity, rather more so in the mar- 
ginal than in the inner tentacles. In a very young specimen sectionized, 
however, I was unable to discover any, even on maceration. 
The mesoglcea of the tentacles is extremely thin, except proximally, where 
it becomes broader and almost homogeneous. The ectodermal muscle is rather 
strong around the base of the tentacles, but weakens distally. Numerous zoox- 
anthellz are present in the thickened endoderm. 
The ectoderm of the dise contains very many, clear gland cells, and a few 
narrow nematocysts, and, in places, large, granular gland cells; endodermal and 
ectodermal musculatures on fine mesoglceal processes are also clearly indicated. 
Zooxanthellz are abundant in the discal endoderm, while few nuclei are to be 
seen in the mesogloa. 
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