REPORT ON THE ANTIPATHARIA. 211 



Aph anipathes sarothamnoides. 



In the genus Aphanipathes, the horny skeleton frequently bears exceedingly long 

 spines, which project into the zooidal tissues in all directions. PI. XIV. fig. 2 shows 

 a subhorizontal section of a zooid of Aphanipathes sarothamnoides in which the 

 spines are shown in transverse section. Two spines are seen to penetrate the transverse 

 mesentery on each side, whilst another is imbedded in the stomodasal ectoderm. In other 

 sections of the same series, taken nearer to the oral surface, the latter spine is seen to 

 project freely into the lumen of the stomodseum. Each spine is surrounded by a sheath 

 of tissue, which is a dilation of the axial skeletal sheath. In transverse section (PI. XIV. 

 fig. 3) the sheath consists internally of a flattened row of cells with oval nuclei, which 

 constitutes the axis epithelium. In the middle is a layer of mesoglcea of variable thick- 

 ness, whilst externally there is a layer of entoderm, consisting chiefly of small cubical 

 cells with round nuclei. The entodermal layer consists usually of only a single row of 

 cells, but in some parts the layer is thickened, and may then be two or three rows 

 deep. 



In sagittal sections the sclerenchyma is seen to be remarkably thick in proportion to 

 the diameter of a zooid, and the coelenteron is reduced to a narrow crescent-shaped cavity 

 between the body-wall and the skeletal sheath. The skeletal sheath has a structure 

 similar to that already described, and differs from that of other genera chiefly on account 

 of the thinness of its entoderm. The axis epithelium is irregularly developed. Usually 

 it consists of a thin flattened row of cells, but at various points, particularly in the angles 

 at the base of a spine, the layer is considerably thickened and the cells composing it are 

 columnar. At a point corresponding to the position of a spine (in sagittal sections) the 

 skeletal sheath becomes evoluted so as to come in contact with the body-wall. The 

 mesoglcea of the skeletal sheath and that of the body-wall are in contact at this point, but 

 so far as I could ascertain they do not become confluent. In such cases, therefore, the 

 coelenteron is perforated by a number of vertical columns of tissue, each of which encloses 

 a spine. 



Ectoderm. — The ectoderm is about 35 //. thick and does not become so much reduced 

 at the base of a zooid as in some other forms. That of the tentacles is papillose ; each 

 papilla contains a central battery of nematocysts and a peripheral ring of granular gland 

 cells which are closely packed. In sagittal sections the gland cells are seen to be large, 

 and filled with deeply-stained granules. The gland cells do not extend to the base of the 

 layer, as in Antipathella and Leiopathes, but have an arrangement similar to those of 

 Antipathes. The lower portion of the layer is occupied by nucleated fibres in the usual 

 manner, which terminate in a thin nervous layer. A row of ectodermal muscular fibres 

 is also present, applied to the outer surface of the mesoglcea of the tentacles and body- 

 wall, but is not well developed. 



