208 THE VOYAGE OF H.M.S. CHALLENGER. 



the middle of each side of the stomodseum is also slightly folded. A little lower down 

 these lateral folds become more important, and the lumen is for some time cross-shaped. 

 The stomodseuni reaches nearly to the base of the zooid, and in its lower portion the 

 lateral folds become so important as to bring about a considerable elongation in the 

 transverse axis. In this part, therefore, the lumen of the stomodseum corresponds in 

 shape with that of Amphianthidse. The ectoderm of the stomodseum is continued on to 

 the free border of the transverse mesenteries as in other forms. In transverse vertical 

 sections, passing in a plane a little to one side of the transverse mesenteries, the 

 stomodseum is seen to be continued laterally nearly to the extremity of the zooid, and 

 ends at a point under the lateral tentacles (see PI. XV. fig. 1, right half of figure). 

 The change in the position of the long axis of the stomodseum is also well shown in 

 transverse vertical sections. In PI. XV. fig. 1, the upper portion of the lumen is slit-like, 

 and the greatest diameter is in a plane at right angles to the one figured. Below, the 

 transverse elongation is considerably greater than that in the sagittal axis. 



Ectoderm. — The surface ectoderm of the tentacles is slightly raised into small rounded 

 papillse, the centre of which is occupied by a bundle of nematocysts, whilst a few deeply- 

 stained granular gland cells are distributed at various points around the periphery. The 

 papillse are about 0'06 mm. in diameter. They are very numerous near the apex of a 

 tentacle, but gradually become more isolated below. 



In longitudinal sections of a tentacle the individual nematocysts of a battery are all 

 subparallel and at right angles to the surface. The ectoderm is here 38 ll thick, 

 and the batteries of nematocysts are about 35 jx in diameter. The nematocysts are of 

 considerable length (27 /*) in proportion to the thickness of the ectoderm, and the 

 area beneath them is probably occupied by slender fibres, the large nuclei of which 

 were, however, only observed. The granular gland cells arranged around each battery are 

 neither so numerous nor so regularly arranged as those of Antipathes dichotoma. In 

 sections parallel with the surface of a tentacle the granular gland cells are seen to be 

 arranged singly or in pairs at various points around the periphery of each battery, but 

 there is usually a considerable interval between them. Near the apex of a tentacle the 

 surface ectoderm consists almost entirely of batteries of nematocysts, but towards 

 the middle they become more isolated, and on the body-wall are separated by intermediate 

 masses of tissue, which may be 67 /a or more in width. These intermediate areas 

 contain oval hyaline cells, each provided with a round nucleus. They sometimes appear 

 to be imbedded in a protoplasmic reticulum containing nuclei, but in other parts distinct 

 spindle-shaped cells may be observed between them, extending from the nervous layer 

 to the surface. Each cell has a median protoplasmic dilation in which a deeply-stained 

 round nucleus is situated. The nervous layer is not important, but a few small ganglion 

 cells have been observed at its base. An ectodermal muscular layer is very imperfectly 

 developed, but a few delicate fibres occur applied to the mesoglcea. 



