REPORT ON THE PENNATUIjIDA. 83 



only extending about half-way from the lower end of the stomach to the 

 bottom of the body-cavity : these are the short mexentrrialjilainents. 



In the sections drawn in Figs. 13, 14, and 15, the septa bovmding 

 the left hand compartments are those which bear the long mesenterial 

 filaments, so that the plane of symmetry, as defined above, passes 

 between them, and therefore divides the mesenterial filaments, as it 

 divides the retractor muscles and the stomach, into two perfectly 

 symmetrical halves. 



The structure of the mesenterial filaments is shown in Figs. 10 

 and 14 : each is a single band, although, owing to its convolutions, it may 

 be cut more than once in a single transverse section (Fig. 14). Each 

 filament consists of a central mesodermal connective tissue lamella, 

 continuous with that of the septum, and clothed by a thick layer of 

 endodermal cells of a special character. These cells are of two chief 

 kinds : — (1.) Columnar ciliated cells ; and (2) large granular gland-cells. 

 These latter are very numerous, and give the special character to the 

 filaments. Numerous spherical nucleated cells, similar to those 

 described as occurring in the cavities of the tentacles, are found 

 lying in contact with the endoderm cells, and apparently belonging to 

 them (Fig. 14.) 



The structure of the long mesenterial filaments is very similar to 

 that of the short ones ; the endoderm is, however, distinctly thinner, 

 and the gland cells not so numerous relatively to the ciliated cells. 



Notwithstanding very careful examination, we have failed to 

 detect thread-cells in the mesenterial filaments of Funiculina. From 

 the descriptions of Gosse, Heider, the Hertwigs, etc., thread-cells 

 appear to be present in the mesenterial filaments of all other Actinozoa 

 that have been examined hitherto, so that if they be really absent in 

 Funiculina the point would be important. It is, however, a difficult 

 matter to establish a negative, especially in histology ; and bearin" in 

 mind the facts that our specimens were neither examined perfectly 

 fresh, nor were prepared for the purpose of histological examination, 

 we can mex-ely record that we have failed to find them. There is, 

 perhaps, no point on which we have more reason to regret the 

 imperfect histological condition of our specimens than the present 

 one, for the presence of thread-cells in the mesenterial filaments, 

 i.e., endoderm, of Actinozoa in general, has always been a great 

 difficulty to morpliologists, who are inclined to view thread-cells as 

 belonging properly to the ectoderm only, so that their absence from 

 the endodei'm of Funiculinn, should it prove to be a real and constant 

 one, would become a point of much interest and importance. 



Gosse, in his account of the mesenterial filaments of the Sea- 

 anemones,* describes them as of two kinds, which he distinguishes by 

 the names of craspeda and acontia, assigning the former name to the 

 thickened cox-d-like edge of the mesenteries, and the latter to certain 

 spirally-twisted threads similar in structure to the craspeda, and 



* Gosse, op. cit., Introduction, pp. xxiii-xxix. 



