DR. A. FAttRE ON THE STRUCTURE OF THE C1LIOBRACHIATE POLYPI. 39,3 
of the stomach are thickly studded with spots of a rich brown colour. These appear 
to be hepatic follicles, and to prepare a fluid that tinges the whole organ, as well as 
its contents, of a similar hue. 
From the upper part of the stomach, and by the side of the entrance from the giz- 
zard, arises the intestine (a 6.), by a distinct pyloric orifice ( a 5.) that is surrounded 
by vibrating cilia. The intestine passes up straight and narrow by the side of the 
oesophagus, from which it is entirely separate and free, and terminates by a distinct 
anal orifice (a / •) in the delicate parietes of the body, close to the outer side of the 
tentacular ring. The parietes of the intestine are marked with pale spots, something 
like those of the pharynx, and the whole tube, like the rest of the alimentary canal, 
possesses a high contractile power. Thus the alimentary canal consists of pharynx 
or oesophagus, gizzard, stomach and intestine, with subsidiary secreting follicles, and 
distinct oral, cardiac, pyloric, and anal orifices. The whole floats freely in a visceral 
cavity, the boundaries of which are formed by the delicate transparent parietes of the 
animal ; the space between the alimentary canal and the parietes being occupied by 
a clear fluid, and by the muscles which act upon the animal. 
That the animal possesses distinct membranous parietes separate from the walls of 
the alimentary canal, and independent of the cell which it inhabits, does not at first 
sight strike the observer, but the slightest attention to points hereafter to be men- 
tioned will place this matter beyond a doubt. 
The transparent horny cell which closely embraces the body of the animal is nearly 
unyielding in its lower two thirds, but terminates above by a flexible portion, which 
serves to protect the upper part of the body when the whole is expanded, in which 
state it is of the same diameter as the rest of the cell; but when the animal retracts is 
folded up and drawn in after it, and completely closes the mouth of the cell. 
The flexible part consists of two portions, the lower half being a simple continua- 
tion of the rest of the cell ; the upper consisting of a row of delicate bristle-shaped 
processes or setse, which are arranged parallel with each other round the top of the 
cell, and are prevented from separating beyond a certain distance by a membrane of 
excessive tenuity, which surrounds and connects the whole. This mode of termina- 
tion of the cell is one of constant occurrence, as will be described in other species, 
and is evidently a provision for allowing of the freest possible motion of the upper 
part of the body in its expanded state, to which it affords at the same time support 
and protection. 
The mechanism by which the acts of protrusion and retraction are effected is some- 
what complicated, and these acts are usually performed with such rapidity, especially 
that of retraction, that it was only by perseveringly watching the animals for several 
hours together, and sketching down each step of the process, whenever I could catch 
more than a momentary glance of one of them in any intermediate position, that I 
was at length led to a satisfactory knowledge of the precise mode of performing these 
operations. 
