Part II. — Stichodactylince and Zoanthcce. 183 



epithelium, and in the lattei' is considerably folded in preserved material, the 

 foldings being followed by the mesogloea. A cuticle is not distinguishable. 



The mesogloea is very variable in thickness, owing to its numerous foldings. 

 It is remai'kably clear and homogeneous ; no fibrillar structure is indicated, and it 

 is practically devoid of any structural elements, isolated ceils occuring with 

 extreme rarity. Even after the other structures of the polyps have been deeply 

 stained the mesogloea remains colourless and indistinguishable from the field of the 

 microscope. The same phenomenon is presented throughout the polyp, and 

 evidently throughout the genus, and is that characteristic of the mesogloea of the 

 Madreporaria. 



The endoderm of the base and column is scarcely narrower tnan the ectoderm, 

 and gland cells with dense, highly-refractive contents, occur sparingly. Zooxan- 

 thellse are absent throughout the polyp. The circular endodermal muscle is 

 feebly developed in the base, but becomes stronger in the column, being sup- 

 ported on small mesogloeal plaitings, and enlarges distally to form the sphincter 

 muscle. 



The sphincter muscle (PI. xiii., fig. 3) is endodermal, and intermediate in 

 character between a diffuse and restricted form. The muscles fibres are very 

 strong and closely arranged, and become concentrated on long mesogloeal pro- 

 cesses ; these latter, however, never become so long and branching as in C. viridis 

 and C. carnea, but are stronger than those of C. australis. 



The knobs of the tentacles consist almost wholly of a very deep ectoderm ; 

 the mesogloea and endodcDu extend into them but a short distance, and they never 

 exhibit any lumen. 



An outer broad zone of the ectoderm is largely made up of very long, narrow 

 nematocysts showing the internal spiral thread distinctly. Occasionally a large, 

 oval, stinging cj'st is also seen, and in the deeper parts of the ectoderm are 

 abundant, oval-shaped, deeply-staining bodies, evidently nematocysts in various 

 stages of development, though some are granular gland cells. The endoderm 

 contains an extraordinary quantity of granular pigment matter. 



The ectoderm of the stems (PI. xiii., fig. 5) is devoid of nematocysts, and in 

 structure is much like that of the column-wall, being highly glandular. A weak 

 ectodermal musculature is supported on branching, mesogloeal processes. From the 

 muscle fibres on these processes very delicate fibrils radiate in a peculiar brush- 

 like manner. The muscle is better developed proximally than distally, and is 

 practically absent from the knob. Internally the mesogloea forms deep, rounded 

 plaits recognizable in longitudinal sections. The endodermal muscle is very 

 weak, and the endoderm contains but little of the granular matter so abundant in 

 the knob ; the tissue nearly fills the lumen in retracted examples. 



The disc closely resembles the stem of the tentacles in structure ; the mesogloea 



2D2 



