46 Proceedings of the Royal Physical Society. 



Pennatulida/ the mesenteries are symmetrically arranged 

 (PL L, Fig. 18), the pair at one end of the body having their 

 muscular faces turned towards each other, while those at the 

 opposite end have them turned away. 



Further down the body, below the gastric tube, the 

 mesenteries become even more complicated. Their inner 

 free edges, which are continued down from the lower end of 

 the gastric tube are greatly and irregularly thickened, con- 

 voluted, and frequently joined together to form the craspeda 

 or mesenterial filaments ^ (PL II., Fig. 9). The result is that 

 the edge of the same mesentery may be cut several times in 

 the same section, and thus variously complicated figures are 

 produced. The thickenings which constitute the craspeda are 

 almost entirely due to the growth of the endoderm covering 

 the edge of the mesentery, although the mesoderm is also 

 increased and continued into the branched and convoluted 

 endodermal processes as a homogeneous supporting layer. 



The endoderm cells of the mesenteries form a continuous 

 layer throughout, covering both faces and the free inner edge 

 below the gastric tube, and being in direct continuity with 

 the endoderm layer lining the body wall, and that coating the 

 outer surface of the gastric tube. The cells (PL III., Fig. 8, en.) 

 are rounded, or of short columnar or cubical form usually one 

 layer deep, but in some places an inner very delicate layer of 

 flattened cells is distinctly visible lying between the ordinary 

 endoderm cells and the layer of muscular fibres. These inner 

 cells do not form a continuous layer (PL III, Fig. 7, n. c). 

 They are of various shapes — fusiform, triangular, and poly- 

 gonal, and their angles are continued into delicate fibres 

 which occasionally anastomose. The cells are distinctly but 

 minutely granular, and have large circular nuclei with dis- 

 tinct nucleoli. The whole appearance of the layer suggests 

 that it is nervous, and as such I consider it, but I was un- 

 able to make out with certainty the presence of this system 

 under the epithelial layers in other parts of the body. 



1 See Marshall, Report on the Oban Pennatulida, Birmingham, 1882. 



2 From Krukenberg's experiments (Vergleichend physiologische Studien 

 an den Ktisten der Adria. 1st Abth. Ueber den Verdauungsmodus der 

 Actinien, 1880), it is most probable that these craspeda are digestive in their 

 function. See also Marshall, loc. cit. 



