]6 DIGESTIVE SYSTEM. 



a. FhylactolcEtnata. 



The moidli (PL II, fig. 24, d) is ra simple edentulous orifice of a circular or slightly 

 crescentic form, placed in the centre of the body of the lophophore, and consequently 

 occupying the bottom of the tentacular crater. Its margin is slightly elevated, and is 

 continuous on the neural side, with a hoi ow valve-like organ (e) of very peculiar formation. 

 This organ arches over the mouth, and may be aptly enough compared in shape to the 

 epiglottis of certain mammifers. The cavity in its interior communicates through an 

 opening (e') in the lophophore with the perigastric space ; the walls which are turned 

 towards the mouth are thick, and densely clothed on their external surface with vibratile cilia, 

 while those which look towards the vent are thin, membranous, and transparent, and destitute 

 of cilia. It may be observed, when the polypide is exserted from its cell, to be in a constant 

 motion, which consists in an alternate elevation and depression of the organ. The elevation is 

 efi'ected by distinct muscular fibres (»), which are visible through the transparent walls, and 

 will be afterwards more particularly described, while the depression is probably the result of an 

 antagonistic elasticity. I propose to designate this organ by the name of ejnstome. On its 

 true function I am unable to throw any light ; though it is here described in connection with 

 the organs of digestion, its relation to the digestive system is perhaps very remote. It may 

 possibly be more correctly viewed as connected with sensation. Its homological import will 

 be afterwards considered. 



From the mouth an wsophagiis (PI. II, fig. 24; V, fig. 5; IX, fig. 7,/) of considerable 

 length leads downwards to the stomach ; it becomes gradually narrower as it approaches the 

 latter, into which it opens by a very distinct conical projection (PL III, fig. 7,/'). 



To the oesophagus immediately succeeds the stomach, without the intervention of any dis- 

 tinct gizzard, such as we find in BowerbanJcia and certain other marine Polyzoa ; and I cannot 

 explain the statement of so excellent an authority as Siebold, who asserts that he has seen in 

 Alcyonella a gizzard with an organization precisely similar to that of Boiuerbankia* The 

 stomach is a large thick-walled sac, and may be divided into two portions, first a nearly 

 cylindrical prolongation (PL V, fig. 5 ; IX, fig. 7, y), which by one extremity immediately 

 receives the oesophagus, while by the other it is continuous with the remaining portion of the 

 stomach ; it may be called the cardiac cavity of the stomach. The second division (/) forms 

 the greater portion of the stomach ; it is also of a nearly C3dindrical form ; but it is longer 

 and wider than the cardiac cavity with which its axis is nearly continuous ; it terminates 

 below in a rounded cul-de-sac ; to distinguish it from the other, I shall call it the pyloric 

 cavity of the stomach. Between the cardiac and pyloric cavities there is no marked line 

 of demarcation, the structure of both being quite similar ; notwithstanding, however, the 

 similarity of structure, I believe there are physiological grounds for the distinction, for I 

 consider the cardiac cavity as the true homologue of the gizzard in BowerbanUa. 



On a level with the continuation of the cardiac into the pyloric cavity arises the 

 intestine ih) ; it springs from the pyloric cavity, with which it communicates by a very defined 

 orifice (PL III, fig. 7, //). The structure of the pylorus is such as to admit of the orifice 



* ' Lehrbuch der Vergleichenden Anatomic,' § 38, Note 1. 



