IV 



VERMES INTESTINAL CANAL 



203 



anterior soft-skinned portion, whose papillae then lie externally. The 

 anterior soft-skinned portion, therefore, is turned outwards like the 

 finger of a glove, and the pharynx proper is pushed after it. The 

 protrusion takes place either through pressure of the perienteric fluid 

 in consequence of a contraction of the dermo-muscular tube, or by the 

 contraction of special protractors of the pharynx. The withdrawal is 

 effected by means of special retractors. This is the most common 

 arrangement of the pharyngeal apparatus (Fig. 132). 



2. The anterior soft-skinned portion is wanting, or is very weakly 

 developed. The mouth then leads almost directly into the muscular 

 pharynx, which is itself evaginated so that when protruded its inner 

 surface comes to lie outside (e.g. in the Capitellidce, Fig. 133). 



3. The pharyngeal apparatus consists of two portions, one above 

 the other, the upper one of which (oesophagus) is less muscular and 

 forms the communication between mouth and intestine; while the 

 under one (jaw- carrier), which is blindly closed and enters the 

 oesophagus in front, is extremely muscular and carries hard jaws, 

 which are generally numerous, in special folds and sacs. These jaws 

 come to the exterior when the pharynx is protruded, and can be moved 

 one against the other (Euniddee, Fig. 134). 



vn. 



FIG. 133. Representation of the 

 pharyngeal apparatus of an Anne- 

 lid, second diagram, g, Brain ; ph, 

 pharynx ; rt, retractors ; mh, buccal 

 cavity; vd, oesophagus. A, In a 

 withdrawn condition. B, In a pro- 

 truded condition. 



FIG. 134. Third diagram of the 

 pharyngeal apparatus of an Annelid 

 (Eunicide), withdrawn. g, Brain ; 

 vd, oesophagus; ph, pharynx; pht, 

 pharyngeal sac ; k, jaws ; mh, buccal 

 cavity ; m, mouth ; r, dorsal, &, vent- 

 ral side. 



Among the so-called Archiannelida, Histriodrilus approaches nearest to the third 

 type on account of its ventral pharyngeal bulb armed with jaws. The pharynx 

 (oesophagus) of Polygordius is distinguished by the want of a muscular layer, and by 

 the great thickening of its epithelial wall, which is very thin only in the ventral 

 middle line. Under the pharynx there lies a thin-walled channel, closing blindly 

 and communicating by a longitudinal slit with the pharynx. In Protodrilus a 

 muscular accessory organ, bent- in the shape of a U, and lying under the beginning of 



