THE STRUCTURE AND RELATIONS OP TUBIPORA. 565 



carmine ; the more peripheral cells are much larger, and after 

 even prolonged soaking in various staining fluids retain their 

 peculiar brown colour. I have noticed the same peculiarity in 

 the endoderm cells of the Gorgonidse. These cells are more- 

 over filled with highly refracting bodies, which make it a 

 matter of great difficulty to determine whether they possess a 

 nucleus or not. In Alcyonium the endoderm cells are con- 

 stantly being shed, especially when the colony is in a sickly 

 condition, and then they exhibit a slow and irregular amoeboid 

 movement. From the similarity that exists between the endo- 

 derm cells of spirit specimens of Alcyonium and Tubipora I am 

 inclined to think that in the latter genus also they exhibit 

 amoeboid movement in the living condition. 



The tentacles, eight in number, stand, in the retracted con- 

 dition of the animal, side by side in front of the stomodgeum. 

 They are not withdrawn into tentacular pouches at the side of 

 the stomodeeum as they are in Paragorgia, Sarcophyton, and 

 certain other Alcyonarians, nor introverted as they are in 

 Corallium (Lacaze-Duthiers) and Heliopora (Moseley), but 

 they simply remain, as they are withdrawn, in front of the 

 stomodseum and parallel with one another (fig. 8, T). 



Each tentacle is provided with 14 — 16 pinnuleeon each side, 

 arranged in a single series, but both the number and arrange- 

 ment of these pinnulse varies in the different species. Each 

 tentacle is covered, as previously described, by a ciliated ecto- 

 derm, and internally an irregular cavity communicating with 

 the general body-cavity is lined by endoderm (fig. 8). Be- 

 tween the ectoderm and endoderm there is a thick layer of 

 mesoderm which contains a number of scattered spicules as 

 first described by Prof. Wright (26). 



The stomodspum is, in the retracted condition, thrown into a 

 number of folds, as it is in so many other Alcyonarians. 

 Heliopora (Moseley), Pennatula, &c. (Marshall), (fig. 8, 

 Stem.). Its epithelium is columnar and ciliated, the cilia over 

 the general surface of the stomodseutn being very small and 

 difficult to see in spirit specimens. At first I had some diffi- 

 culty in finding any trace of the siphonoglyphe owing to the 



VOL. XXIII. NEW SER. 1= P 



