74 BICELLARIID^. 



by which it is distinctly separated from the preceding, 

 and which marks it out as a very natural group. The 

 turbinate cell, with the more or less upturned and up- 

 looking aperture, somewhat abruptly bent inwards below 

 towards the median line, which is characteristic of the 

 more typical Bicellarice, gives place in Bugula to an elon- 

 gate, boat-shaped cell, slightly attenuated towards the 

 bottom, and often truncate at the top, the front of which 

 is usually occupied for three fourths of its length or more 

 by the aperture. The latter stretches vertically from the 

 top of the cell downwards; it is not set obliquely, looking 

 upwards ; nor is it so decidedly bent in towards the median 

 line at its lower extremity as in Blcellaria, although, from 

 the peculiar turn of the cells, it is somewhat inclined 

 inwards below. The spines have ceased to be so conspi- 

 cuous a feature, though still present. The cells are more 

 closely united than in Bicellaria ; but the structure is far 

 from solid or compact. The avicularia are developed in 

 great abundance, and often attain a large size. In most 

 cases every cell is provided with one, articulated to its 

 outer side ; and in the living specimen the surface of the 

 zoarium exhibits a strange and animated scene as the 

 multitude of grotesque heads sway themselves to and fro, 

 and snap their tiny jaws, as it seems, with aimless energy. 

 In this genus the polypide exhibits a somewhat strongly 

 marked structural character. The tentacular corona is 

 only just protruded beyond the orifice of the cell ; the 

 pharynx is wide and ample, while, on the other hand, the 

 oesophagus is reduced in size and extremely short. At 

 the bottom of it there is a distinct cardiac valve, and 

 below this a subglobular chamber which opens into the 

 true stomach. The walls of this chamber, as well as of 

 the stomach, are richly coloured by the hepatic glands, 

 which are highly developed. A prolongation of the diges- 



