CCELENTERATA : HYDROZOA. IO9 



marginal bodies likewise communicate with the chylaqueous 

 canals. The reproductive elements " are lodged in- saccular 

 processes of the lower portion of the central cavity, immedi- 



Fig. 26. — Rhizostomidae. Generative zo5id of Rkizosioma (after Owen). a Um- 

 brella; hb '* Stomatodendra," covered with clavate tentacles and minute polypites; 

 fc Anastomosing network of canals. 



ately above the bases of the radiating canals, and, being 

 usually of some bright colour, form a conspicuous cross shining 

 through the thickness of the disc." — (Greene.) 



In the Rhizostomidcs the reproductive zooids (fig. 26) differ 

 from those we have just described as occurring in the first 

 section of the Pelagidce, in not possessing tentacles on the 

 margin of the umbrella, and in having the simple central 

 polypite replaced by a composite dendriform process, which 

 bears numerous polypites, projects far below the umbrella, 

 and is thus described by Professor Huxley : — " In the Rhizo- 

 stomidce (fig. 26) a complex, tree-like mass, whose branches, the 

 ' stomatodendra,' end in, and are covered by, minute polypites, 

 interspersed with clavate tentacula, is suspended from the middle 

 of the umbrella in a very singular way. The main trunks of the 

 dependent polypiferous tree, in fact, unite above into a thick, 

 flat, quadrate disc, the ' syndendrium,' which is suspended by 

 four stout pillars, the ' dendrostyles,' one springing from each 



