394 Prof. J. Reid on the Anatomy and 
cula, by the upward 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 sete 
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), were seen among the broken- 
down cells. 
Flustra avicularis. This polype is thrown ashore in great 
quantities after storms, chiefly adherig 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 spmes 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. 12 f), of a hinge- 
process (fig. 12 e), and of a pedicle (fig. 12 6). 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 1s 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 this moveable bird-head process, I have supposed the 
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. 
