362 J. E. Durrpen—Jamaecan Actiniaria: Part I.—Zoanthee. 
condition is described under Jsaurus tuberculatus(p. 347). Fine threads connect one 
group of cells with another. 
The endoderm is a uniformly thin layer, and contains zooxanthelle. A weak 
circular endodermal muscle is present. 
Sphincter muscle (Pl. x1x., fig. 1).—The sphincter muscle is single, mesogleeal, 
and contained in an elongated series of irregular cavities, situated near the 
endoderm; small cavities occur along with larger ones, all forming an irregular 
row. 
Tentacles.—The ectoderm is very thick, consisting of an outer zone of small, 
elongated, narrow nematocysts, and an inner one with deeply-staining nuclei, 
zooxanthellae, and pigment granules. The ectodermal muscle is well developed 
on mesogleeal plaitings. The mesogloea in places is rather thick, and contains 
cell-islets. The endoderm is somewhat high, nearly filling up the lumen; the 
circular muscle is readily seen, forming a very regular layer in longitudinal 
sections. 
Dise (Pl. xix., fig. 4).—The peripheral grooved portion of the disc has a very 
thick, highly glandular, sinuous ectoderm, containing zooxanthelle, small peri- 
pheral nematocysts, and occasional deeper oval ones; also a well developed radial 
muscle. The mesogloea follows the projecting fold, and becomes very thick, and 
may contain a few sand-grains; between the folds it is very thin. The endo- 
derm is the same as elsewhere. In longitudinal sections of contracted specimens 
the part next the tentacles is thick ; it then becomes delicate, and again enlarges 
towards the lips where incrustations occur in the mesoglea. An endodermal 
muscle is present. 
Gsophagus (Pl. x1x., figs. 2, 3).—The cesophagus in different sections is either 
an elongate or a shortened pear-shape, with a well defined cesophageal groove. 
The ectoderm is richly ciliated ; a zone of closely-arranged narrow nemato- 
cysts occurs peripherally, while the nuclei are arranged mostly in a middle zone ; 
pigment matter occurs in the deeper parts, abundantly in some, sparingly in 
others. ‘The ectoderm in most is thrown into folds which vary in number, but 
are generally between eight and eleven; in some sections the ectoderm is 
unfolded. 
The mesogleea is thin, becoming a little thicker at the groove; it does not 
follow the foldings of the ectoderm. 
The endoderm is similar to that in the column-wall, but is slightly deeper 
between the mesenteries. It differs from that of the mesenteries in having little 
or no pigment matter. 
Mesenteries (Pl. x1x., figs. 2, 3)—The mesenteries in most cases present the 
usual brachyenemic type, but irregularities may occur, and opposite sides have 
not always the same number of pairs. The usual arrangement is that of ten perfect 
