Mesenterial Filaments, and Endoderm of Xenia, 445 



remainder of the stomodaeum bear short cilia on their free surface, 

 but among these are numerous "goblet cells" (G, figs. 1 and 2), 

 which have not hitherto been noticed in the stomodeeum of the 

 Alcyonaria. These cells are swollen by some secretion to which they 

 give rise; they generally appear to be empty, having discharged 

 their secretion, which, in some cases, can be seen issuing from the cell 

 into the cavity of the stomodaeum. These secreting cells occur chiefly 

 in the middle and lower portions of the stomodoeum, and are most 

 abundant on the lateral walls near the siphonoglyphe (see fig. 2). 

 They do not occur among the cells which form the siphonoglyphe. 



These " goblet cells " of the stomodaeum are the only secreting cells 

 connected with the digestive cavity which 1 have been able to find, 

 as the six thick short ventral and lateral mesenterial filaments, 

 which bear the gland cells in other Alcyonaria, are absent in all 

 polyps of this Xenia. Only the dorsal mesenteries possess thickened 

 edges forming the two mesenterial filaments which have a similar 

 course and structure to those of Alcyonium. The free edge of the 

 ventral and lateral mesenteries is only very slightly thickened, and 

 the cells which cover this edge differ in no way from those which 

 cover the remaining portions of the mesentery. 



The two new points in the anatomy of this species of Xenia are the 

 presence of gland cells in the stomodaeum and the absence of the six 

 ventral and lateral mesenterial filaments usually present in the polyps 

 of the Alcyonacea. Wilson* (in Kophobelemnon) and Hicksonf (in 

 Alcyonium) have shown that these mesenterial filaments bear the cells 

 which produce the digestive secretion. I would suggest that the 

 absence of these filaments in this Xenia is correlated with the pre- 

 sence of gland cells in the stomodseum, and that these cells, judging 

 from their appearance and position, probably perform some digestive 

 function. 



The siphonozooids which occur in Pennatulids and some other 

 Alcyonaria are the only recorded examples of polyps in which the 

 ventral and lateral mesenterial filaments are absent. According to 

 Wilson these siphonozooids derive their food-supply from the auto- 

 zooids or feeding-polyps, and, therefore, do not require cells to pro- 

 duce a digestive secretion. 



In this species of Xenia, then, the secretion in connection with the 

 digestive cavity is formed, not by endoderm cells, but by cells which 

 are derived from the ectoderm, as, from a study of the buds, I have 

 found that the stomodaeum is ectodermic in origin in this as in other 

 Alcyonaria. 



The endoderm cells which line the ccelentera and the cavities of the 

 tentacles have a similar structure throughout the colony. They are 



* ' Mitt. Zool. Stat. Neapel,' vol. 5, 1884. 



f ' Quart. Journ. Micr. Science,' vol. 37, 1895. 



2 L 2 



