26 . REPORT ON THE PENNATULIDA. 



the tentacles. The tentacles, eight in number, are hollow (Fig. 10), 

 and are fringed on each side by a series of hollow pinnules. 



The tentacles are arranged in a whorl round the mouth (Fig. 10, m), 

 which leads into a short tubular stomach (h) with folded walls, and 

 opening below into the body-cavity. The stomach is connected with 

 the body-wall by a series of eight vertical mesenteries or septa (Figs. 

 10 and 13 o), which extend below the stomach to the bottom of the 

 body-cavity (Figs. 10, 14, and 15). The free edges of these mesenteries 

 below the stomach are thickened, forming twisted cords — the 

 mesenterial filaments (Figs. 10 and 14, ?•, s,) ; of these two are slender 

 and extend the whole length of the body-cavity (Figs. 10, 14 and 15, s), 

 while the other six are thick and short, only extending part of the 

 way down the body-cavity (Figs. 10 and 14 r). The free edges of these 

 six mesenteries bear, below the mesenterial filaments, the reproductive 

 organs (Figs. 10 and 15 t). 



We propose now to describe these several parts in more detail, 

 taking them in the order given above. 



a. The Body-wall. — This consists of a firm gelatinous mesoderm 

 (Figs. 10, 12, 13, and 14,. r), which forms the greater part of the thickness 

 of the wall, and is clothed on its outer and inner surfaces by thin 

 cellular membranes — the ectoderm (2v) and endoderm (y ). 



The ectoderm, which in our specimens is not in good histological 

 condition, appears to consist of a single layer of columnar cells, which 

 are often much vacuolated and contain, especially in their deeper 

 parts, very numerous, minute, highly-refractive particles of a dark 

 brown colour. So far as we have been able to determine, the ectoderm 

 of the body-wall contains no thread-cells ; but on this, and on many 

 other points of interest involving histological determinations, we are 

 unable to speak with certainty, owing to the imperfect preservation 

 of the specimens. 



The mesoderm consists of a matrix of considerable thickness and 

 consistence, which in its outer part is homogeneous, but in its inner 

 portion is, in places, more or less distinctly fibi'illated. Imbedded in 

 the matrix are cells of two kinds :^(1) Spherical nucleated cells, 

 closely resembling ordinary cartilage-cells in appearance ; (2) Fusiform 

 nucleated cells with long processes, which often branch and become 

 connected with the processes of adjoining cells. 



The mesoderm is traversed by a network of very fine canals, which 

 are le&s abundant and of less size in the upper part of the body-wall 

 than at the lower part, whero they become continuous with the canal 

 sj'stem of the rachis, which has already been described. The finer 

 canals do not appear to have distinct walls, but seem to be mere 

 channels in the matrix of the mesoderm ; in the larger canals, how- 

 ever, a very evident epithelial lining is present, which becomes 

 continuous with the endoderm at the points where the canals open into 

 the body-cavity (Figs. 10 and 15). This canal system probably serves 

 to convey nutrient matter from the body-cavity, where it is prepared, 



