REPORT ON THE PENNATULIDA. 221 



left-hand side of Fii,'. 5 : but is of some thickness between the leaves, 

 as shown in the ri.s^ht-hand side of the same figure. It is traversed 

 by a network of very fine canals, and contains also definitely arran.t»ed 

 muscular fibres. These latter are chiefly longitudinal in direction : 

 they form a well-defined layer, with a crenated outline when seen 

 in transverse section, running along the dorsal surface of the rachis a 

 short distance below the surface epithelium (Fig. 6, / in), and a similar 

 layer along the ventral surface, shown in the same figure. In the 

 stalk, according to Kolliker"s descriptions and figures, there is a con- 

 tinuous sheath of muscle extending all round ; but in the rachis this 

 sheath is interrupted at the sides by the polypes, and so loses its 

 regular arrangement. The dorsal and ventral portions remain, as we 

 have just seen, unaltered, but the lateral portions are much changed : 

 they persist in part as the protractor and retractor muscles of the 

 polypes (Fig. G, j)). 



A deeper set of longitudinal muscles is developed in the lower part 

 of the rachis in connection with the inner ends of the polype cavities : 

 it is shown in Fig. 6. 



The polype cavities communicate with the lateral canals, as shown 

 in the right-hand side of Fig. 6 ; but this connection appears only to 

 take place towards the bottom of the rachis. Through its means ova 

 are enabled to pass from the polypes into the lateral canals. 



On the ventral side of the rachis, and along its whole length, there 

 is found a cui'ious system of tubes, which we propose to speak of as the 

 radial canals. These form two lateral masses (Figs. 5 and (5, ik c.) 

 imbedded in the mesoderm on either side of the main ventral canal, 

 each mass consisting of a number of branching tubes of tolerably 

 uniform diameter, lined by a single layer of short columnar epithelial 

 cells, which stain very readily with logwood or other colouring reagents. 

 At intervals these tubes can be distinctly seen in transverse sections of 

 the rachis to open into the main ventral canal, and such openings are 

 shown in both Figs. 5 and 6. 



Just before reaching the main canal the tubes are slightly con- 

 stricted, and their epithelial lining suddenly changes its character, 

 and becomes converted into the much flatter epithelium of the main 

 canals. At their outer ends the radial canals can sometimes be traced 

 into continuity with a system of very fine canals with no distinct 

 epithelial lining, which branch m an irregular way through the meso- 

 derm of the rachis, and communicate both with the polype cavities and 

 with the main canals of the rachis, and which clearly correspond to the 

 fine nutrient canals traversing the mesoderm of both Funiculuia and 

 Peiiiiatula. 



This system of ventral or radial canals has been described carefully 

 by KoUiker in the genus Halisceptrum,* in which its main characters 

 and relations appear to be the same as in Viifiularia, though diffex-ing 



Kiilliker;: np. rit.. pp. 169. 170, 



