362 J. E. Duerden — Jamaican Actiniaria : Part I. — Zoanthece. 



condition is described under Isaurus tuberculatus (p. 347). Fine threads connect one 

 group of cells with another. 



The endoderrn is a uniform^ thin layer, and contains zooxanthellse. A weak 

 circular endoderrnal muscle is present. 



Sphincter muscle (PL xix., fig. 1). — The sphincter muscle is single, mesoglceal, 

 and contained in an elongated series of irregular cavities, situated near the 

 endoderrn ; 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, 

 zooxanthellse, and pigment granules. The ectodermal muscle is well developed 

 on mesogloeal plaitings. The mesoglcea in places is rather thick, and contains 

 cell-islets. The endodertn is somewhat high, nearly filling up the lumen; the 

 circular muscle is readily seen, forming a very regular layer in longitudinal 

 sections. 



Disc (PI. xix., fig. 4). — The peripheral grooved portion of the disc has a very 

 thick, highly glandular, sinuous ectoderm, containing zooxanthellae, small peri- 

 pheral nematocysts, and occasional deeper oval ones ; also a well developed radial 

 muscle. The mesoglcea follows the projecting fold, and becomes very thick, and 

 may contain a few sand-grains ; between the folds it is very thin. The endo- 

 derrn 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 mesoglcea. An endoderrnal 

 muscle is present. 



CEsophagus (PI. xix., figs. 2, 3). — The oesophagus in different sections is either 

 an elongate or a shortened pear-shape, with a well defined oesophageal 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 mesoglcea is thin, becoming a little thicker at the groove ; it does not 

 follow the foldings of the ectoderm. 



The endoderrn 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 (PI. xix., figs. 2, 3). — The mesenteries in most cases present the 

 usual brachycnemic type, but irregularities may occur, and opposite sides have 

 not always the same number of pairs. The usual arrangement is that of ten perfect 



