216 Dr. W. B. Carpenter on the Structure [Jan. 20, 



as being a direct extension of the body-cavity or coslom, I term the eosliao 

 canal. 



Visceral Mass. — The "visceral mass" primarily consists of an alimen- 

 tary canal (not distinctly differentiated into oesophagus, stomach, and 

 intestine), which makes about one fourth more than a single round turn 

 upon itself (bed, fig. 1). From the central mouth this canal at first passes 

 obliquely downwards (b, figs. 2, 3), then changes its direction to the hori- 

 zontal, and, after making somewhat more than a complete circuit, turns 

 upwards again (at d, fig. 1) towards the oral disk, to terminate in a vent 

 which projects upwards from its surface between two of the radial fur- 

 rows, the terminal portion of the alimentary canal being separated 

 from the cavity of the vent by a valvular projection of its lining mem- 

 brane. 



The membranous wall of the alimentary canal may be called its mucous 

 lining. It is somewhat rugose in the first or oblique part of the canal 

 (b, fig. 2); whilst in the horizontal coil it is nearly smooth on the peri- 

 pheral side, but deeply plicated on the central side (fig. 1), there 

 forming, with its epithelial (?) covering, a sort of glandular mass *, the 

 projection of which into the canal considerably narrows it, as shown at 

 e, fig. 2. The whole smooth inner surface of the mucous lining (b, c, fig. 1) 

 is covered with a layer of a yellow substance, which is so soft in the living 

 state that it is difficult to separate it for microscopic examination, but 

 which, when hardened in spirit, readily detaches itself from the sub- 

 jacent membrane in large flakes, which are so opaque as not to be 

 readily examined minutely. The appearances presented by thin sections 

 of this layer, however, dispose me to think that it may be regarded as 

 a columnar epithelium imperfectly differentiated into cells ; and it can 

 scarcely be doubted that the portion of it forming the large gland-like 

 projection just alluded to has an hepatic function. The projecting edges 

 of its plicated surface are fringed with long cilia, whose function is 

 obviously to produce an indraught into the mouth, and to propel the 

 ingested matter along the canal. 



The exterior of the mucous wall of the alimentary canal is not in 

 immediate contact with its peritoneal covering ; but a continuous space 

 is left between them, which is everywhere traversed by lamellae of con- 

 nective tissue passing between the apposed surfaces. This, which I 

 shall call the intramural space, is much more distinct in some varieties 

 of Antedon rosaceus than it is in others — the Lough Strangford variety 

 presenting it in the most strongly marked degree, while in the Plymouth 

 specimens the two membranes approximate each other much more 

 closely, the Clyde variety, which is the one I have most studied, 

 holding an intermediate position in this particular. — The like differ- 



* A section of this portion very closely resembles the arbor vita of the cerebellum, 

 the grey substance being represented by the yellow epithelial layer, and the white by 

 the plications of the mucous membrane and the sinuses which they enfold. 



