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



The stomodseum is similar in structure to that of Parantipathes larix. An ectoder- 

 mal muscular layer has not been observed in the stomodseum. 



Mesoglcea. — In Aphanipathes sarothamnoides the mesoglcea is unusually thick, and in 

 Aphanipathes cancellata, the zooids of which are smaller, it appears to have a similar 

 relative development. In the former species it has an average thickness of 28 jx. This 

 layer appears to be especially thickened in the peristome and body-wall and also in the 

 interzooidal areas (cf. PI. XIV. fig. 2). The mesoglcea is, however, homogeneous through- 

 out, and no fibres or connective-tissue cells have been observed within it, such as occur in 

 that of Cladopathes plumosa and many Actiniaria. 



Entoderm. — The entoderm varies from 11 to 28 /a in thickness, and presents no 

 features of especial interest. It appears to consist largely of small cubical cells, and is 

 not so richly supplied with hyaline gland cells as that of many other genera. An ento- 

 dermal muscular layer has not been observed. 



Pteropathes fragilis. 



The stomodseum of this species is very much folded, and may be best studied by 

 means of a series of horizontal sections. In the upper portion of the oral cone there are 

 usually eight radiating folds, and the lumen is longer in the transverse than in the 

 sagittal axis. At a lower level the lateral folds are much more pronounced, and one or 

 two near each extremity of the sagittal axis become much elongated and are curved 

 inwards, so as to take up a transverse position. Each fold contains a lumen which 

 communicates with the general stoinodseal cavity, but this is usually very narrow, and 

 the ectodermal walls are often in contact. In the middle section of the stomodseum the 

 lumen becomes narrowed, and is much elongated in the sagittal axis, so that the directive 

 mesenteries have only a short course in this region. An oblique section of the stoniodseum 

 is shown in PL XIV. fig. 4, which also shows one pair of directive mesenteries. I am 

 not aware of the existence of such a complicated system of folds in the stomodseum of 

 any other Antipatharian. 



Ectoderm. — The ectoderm of the tentacles is papillose, and the papillae are frequently 

 constricted at the base and appear club-shaped in transverse sections. Each papilla 

 contains a central battery of elongate nematocysts, and a number of large granular 

 gland cells are distributed irregularly around the periphery. The gland cells of the surface 

 ectoderm stain more deeply in hsernatoxylin than those of any other part. Ectodermal 

 muscular fibres are present, but not very well developed. 



In the stomodseum the surface layer consists chiefly of ribbon-like " Stiitzzellen" and 

 slender fibres, both of which apparently extend from the surface to the nervous layer 

 adjoining the mesoglcea. The former appear to have the nuclei contained within the 

 surface dilation of protoplasm, whilst the nuclei of the fibrous cells usually occupy the 



