REPORT ON THE PENNATULIDA. 



Confining the term zooid to the small individuals destitute of 

 tentacles, the arrangement of the polypes and zooids on the rachis is as 

 follows: — At the lower end of the i-achis there are no polypes at 

 all, and merely a single longitudinal row of small zooids, situated 

 along the ventro-lateral angle of the quandrangular rachis. Passing 

 upwards, the zooids increase in both size and number, and pass 

 obliquely across the side of the rachis to the dorso-lateral angle, which 

 they reach about 2 ins. above its commencement. Above this point 

 they gradually shift on to the dorsal surface, where they form an 

 interrupted and irregular longitudinal median row from three to five 

 zooids wide, extending to the extreme top of the rachis. 



The first polypes are found about 2 ins. above the commencement of 

 the rachis, and on the middle of the lateral surfaces. They lie on the 

 ventral side of the zooid rows, and arc at first in a single row on either side, 

 and at rather wide intervals apart. About an inch higher up the rows 

 become double, and beyond this point the polypes increase rapidly in 

 number and size. For a short distance they are clearly arranged in 

 oblique rows, ascending from the ventral side below to the dorsal side 

 above ; bub along the greater part of the rachis they are clustered so 

 closely together that it is difficult to make out any definite arrangement 

 in rows, though a closer examination shows, as Kolliker has already 

 pointed out,* that they are really arranged in ill-defined, somewhat 

 triangular groups, the apices of the triangles being situated on the 

 ventro-lateral angles of the rachis and about J in. apart, while the 

 bases are on the dorsal surface in contact with the median zooid tract. 



The polypes cover the whole of the lateral surface of the rachis 

 and the marginal portion of the dorsal surface, but do not extend on 

 to the ventral face (Figs. 3, 4, o). Throughout the whole length of 

 the rachis the polypes on the dorsal surface are the smallest, those on 

 the lateral surface gradually increase in size, and those along the 

 ventro-lateral angle are the largest of all (Fig. 3). These latter may, 

 as shown in Fig. 5, encroach somewhat on the ventral surface. 



The polypes are largest and most closely placed in the uppermost 

 12 ins. of the rachis, where they form a thick heavy mass, completely 

 weighing down the top when taken out of water. The greatest width 

 of the rachis, at 6 ins. from the top, is | in. 



The ventral surface has an average width of 0-14 in. It is not 

 perfectly straight throughout, but becomes curiously twisted at one or 

 more points, the most marked of which is 10§ ins. from the upper end, 

 and is indicated in Fig. 1. These twists are apparently due to some 

 irregularity in growth, though it is quite possible that the fleshy 

 cojnenchym, as shown by Sir J. Dalyell, to occur in ViriiuIaria,-\ 

 may be able during life to twist itself round the calcareous stem, and 

 so cause the distortion in question. 



* Kolliker, op. cit., p. 257. 



t Sir John Graham Dalyell, " Eare and Remarkable Animals of Scotland," 

 1848, Vol. ii., p. 185 



