REPOKT ON THE l>ENNATUIilDA. 145 



EEPOET ON THE PENNATULIDA 



COLLECTED IN THE OBAN DEEDGING EXCURSION 



OF THE BIRMINGHAM NATURAL HISTORY AND 



MICROSCOPICAL SOCIETY, JULY, 1881. 



BY A. MILNES MARSHALL, M.A., D.SC, PROFESSOR OF ZOOLOGY 

 IN OWENS COLLEGE, AND W. P. MARSHALL, M.I.C.E. 



( Continued from page 128. ) 



3. — The Polypes and Zooids — 



The differences between the two kinds of individual animals, 

 polypes and zooids, composing the colony, are far more marked in 

 Pennatula than in Fuiiiculiiia, owing mainly to the fact that instead of 

 both polypes and zooids being inserted separately into the rachis, the 

 polypes are fused together to form the leaves, while the zooids, as in 

 Funiculina, are planted independently of one another. 



The structure of one of these leaves is shown in Fig. 3. Each 

 leaf is triangular in shape, having a short base by which it is attached 

 to the side of the rachis, and long dorsal and ventral borders. The 

 leaf consists of a number of polypes placed side by side and fused 

 together along nearly the whole of their length, the distal or mouth 

 ends along being free. It is important to realise this fully, and to 

 avoid the very common error of speaking of the polypes as " borne 

 on or by the leaves." The leaves simply consist of the polypes, each 

 one of which is directly attached to the rachis. 



The free or oral ends of the polypes are situated along the dorsal 

 border of the leaf ; and each polype, as is clearly shown m Fig. 3, 

 extends down to the rachis and is separately inserted into it. The 

 consequence of this is that the several polypes composing a leaf are of 

 very different lengths, the ones whose mouths are nearest the median 

 plane of the whole Pennatula being very short, while those whose 

 mouths are at or near the apex of the leaf are of very great length. 



It will further be seen from the figure that while the base of the 

 triangular leaf is formed by the lower ends or bases of the several 

 polypes, and the dorsal border by their free oral ends, the ventral 

 border is formed exclusively by the most ventrally situated of the 

 component polypes, which is also the longest of the whole set. The 

 dorsal and ventral boi'ders of the leaf are not quite straight, but 

 curved as shown in the figure. 



The number of leaves in the male specimen is thirty-six on either 

 side, and in the female thirty-four. The leaves are not arranged 

 strictly in pairs on the opposite sides of the rachis ; at certain parts 

 they may be so paired, while in others they alternate regularly. The 

 successive leaves are, as shown in Figs. 1 and 2, placed very close 

 together, their bases being separated by only a thin strip of the side 

 of the rachis, less than half the thickness of a leaf. 



