394 Prof. J. Reid on the Anatomy and 



cula, by the upwai'd motion of which the eversion of this flexible 

 tube is effected, are now seen lying within it. The third stage 

 in the protrusion of the polype is the passage of the tentacula 

 and pharynx through the upper aperture of the flexible tube. 

 The greater part of this tube appears to be composed of setae 

 connected together by a membrane. The polype has fifteen or 

 sixteen tentacula. By breaking up a number of the cells I pro- 

 cured two of the polypes nearly entire, and the stomach and its 

 appendix had nearly the same relative size as in Crisia chelata. 

 Several bodies, each composed of reddish brown nucleated cells 

 inclosed in a membrane (ova), w^ere seen among the broken- 

 down cells. 



Flustra avicularis. This polype is thrown ashore in great 

 quantities after storms, chiefly adhering to the roots of Flustra 

 foliacea and F. truncata. The cells have almost always four hol- 

 low spines, adhering to the upper margin of the cell, two to each 

 angle. The two superior spines are pretty long- and project up- 

 wards and outwards, and the two inferior, which are placed close 

 to the two superior at their origin, are considerably shorter and 

 less thick, and project generally inwards, forwards and a little 

 downwards. In a few cells I have seen five spines attached to 

 the superior margin, three of these adhering to the outer angle. 

 The bird-head processes attached to the outer edges of the 

 branches of the polypidom are generally very considerably larger 

 than those nearer their centres. Each bird-head process may 

 be described as being composed of a body (fig. 13/), of a hinge- 

 process (fig. 12 e), and of a pedicle (fig. 12 b). By the pedicle 

 it is attached to the interior of a round hollow process projecting 

 slightly from the anterior surface of the polypidom (fig. 12 a). 

 The body of the bird-head process* is very convex along the 

 lower edge, and it is elongated from below upwards and some- 

 what flattened transversely. It is divided by an oblique ridge on 

 its interior surface into two chambers (fig. 12 d), which com- 

 municate freely at the superior and middle parts at least. The 

 hinge-process is articulated to the superior or concave surface of 

 the body by a hinge-joint, along the line of the superior termina- 

 tion of the internal ridge which divides the body into two parts. 

 The edges of the concave surface are thickened at this part, and 

 present a slight depression on each, for receiving the two articular 

 processes of the hinge-process. The body of the bird-head pro-? 

 cess is hollow, and its concave surface presents three apertures ; 

 the largest of. these is the uppermost, and is separated from the 

 middle by a bar stretched across between the articular cavities 



* Jn describing tliis moveable bird-head process, I have supposed Ihe 

 polypidom to be erect, and the concave surface of this process to be looking 

 upwards in the direction of the long axis of the cells. 



