BRITISH ZOOPHYTES. 191 



Zoantliarla^ but the mouth, which is a mere slit, opens 

 iuto the oesophagus, which leads into the stomach. 

 The latter communicates directly with the body cavity. 

 The endodermal cells of the stomach often contain 

 granular particles of a dark colour, of doubtful function. 

 The mesenteries or septa connect the stomach with the 

 body wall, and divide the body into chambers. Plate XV., 

 fig. 2. The structure of the septa is similar to that of the 

 same organs in the Zoanthaxna, consisting of a mesoderm, 

 lined on each side by endodermal cells, and well pro- 

 vided with muscular fibrilla3. The mesenteries extend 

 below the stomach, and hang downwards towards the 

 bottom of the body cavity. These filaments occur in 

 two forms, — long filaments , which are slender and reach 

 to the bottom of the body cavity (there are two of 

 these), and sliort filaments, which are thicker and 

 shorter. The filaments have thickened, cord-like edges, 

 which are analogous to the crasi^eda of the Zoantharia, 

 and generally contain thread-cells. The polyps, like 

 those of the Hydroids, are connected with each other 

 by canals which extend throughout the coenenchyma, 

 or fleshy substance of the colony. 



Reproduction is by ova, and gemmation. The ova 

 are developed in ovaries sometimes borne at the free 

 ends of the short mesenteries, and sometimes placed in 

 expansions of the coenenchymal canals. The sexes 

 ai-e believed to be distinct, each colony being either 

 male or female. 



In addition to the mature and perfect polyps there 

 are also in the Pennatulida rudimentary polyps, which 

 have neither tentacles nor reproductive organs. Their 

 function is supposed to be to preside over the intro- 

 duction of sea water into the colony. 



