254 J. H. ASHWORTH. 



mesenterial filaments are absent. According to "Wilson (1884), 

 these siphonozooids derive their food supply from the autozooids 

 or feeding polyps^ the dorsal mesenterial filaments of the former 

 creating upward currents which cause a flow of fluid from the 

 autozooids to the siphonozooids, through the canals which 

 connect them together. Food undergoes digestion in the 

 autozooidsj and some of the products are passed on to the 

 siphonozooids, hence the latter do not require cells to produce 

 a digestive secretion. 



In this Xeniathe 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 stomodseum is ectodermic in origin in this as 

 it is in other Alcyonaria (Wilson, 1883). Since the absence 

 of ventral mesenterial filaments in Xenia Hicksoni was 

 proved I have carefully examined all the other specimens of 

 Xenia at my disposal. These are sixteen in number, viz. one 

 from Talisse Island, North Celebes, one from Rotuma, Fiji 

 Islands, and fourteen from various reefs in the Pacific. In 

 all these the ventral and lateral mesenterial filaments are 

 absent, there being only a very slight thickening of the free 

 edges of the mesenteries, this thickening being entirely due to 

 a slight increase in the amount of the mesogloea along the free 

 edges. In all the specimens the two dorsal mesenterial 

 filaments are present, and have the typical course and struc- 

 ture. In Heteroxenia Elizabethse the two dorsal mesen- 

 terial filaments only are present. The absence of ventral and 

 lateral mesenterial filaments may, therefore, be considered as 

 one of the characters which distinguish the polyps of the genera 

 Xenia and Heteroxenia from those of other Alcyonaria. 

 In two at least of the specimensof Xenia^ from Dr. Willey's 

 collection some of the cells of the stomodseum are goblet-like, 

 and similar to those described above in the stomodseum of 

 Xenia Hicksoni. 



Coelentera of Polyps. — The other parts of the colony 

 present a structure similar, in the main features, to that 



' X. crassa, Sclieiik, and X. viridis, Sclienk. 



