594 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



In sections through the upper regions of the polyp the continuity of the mesenteries is often 

 interrupted by the presence of synapticular perforations; further, some of the mesenteries are 

 continuous from one polyp to another. The continuity of the mesenteries of contiguous polyp- 

 is without doubt to be associated with the absence of distinct polypal limitations noticed among 

 the external characters, and also with the confluent septo-costse characteristic of the genus; 

 probably also it has some bearing upon the method of asexual growth of the colony, which calls 

 for more detailed study. 



Mesenterial filaments occur on all the mesenteries, but in the upper region are very 

 rudimentary in character, and imperfectly separated from the mesenterial epithelium. In the 

 lower region of the polyp many of the filaments undergo an enormous development in connection 

 with the convolution of the mesenteries. They mostly till the septal loculi, and bear numerous, 

 closely arranged, large nematocysts, and many clear, brightly staining gland cells, and others 

 with coarsely granular contents. 



The skeletogenic ectoderm is rarely determinable in ordinary decalcified material, but 

 desmoidal processes are numerous along the line of attachment of some of the mesenteries. The 

 skeletotrophic endoderm remains a very narrow layer throughout, undergoing but little increase 

 in thickness in the lower regions. 



In the ordinary condition of retraction the gastro-ccelomic cavity is very limited in extent. 

 The central cavity is prolonged upward and outward betw T een the mesenteries and the septa as 

 far as the edge of the theca. and is there placed in communication with that of adjacent polyps 

 (fig. 162). Downward the cavity soon diminishes in peripheral extent, and centrally is broken 

 up into distinct chambers by the inward growth of the septal invaginations which meet in the 

 middle. For some distance the interseptal loculi are crowded with the enlarged and convoluted 

 mesenterial filaments. 



