204 COMPARATIVE ANATOMY CHAP. 



the intestine, enters the pouch-shaped non-muscular oesophagus quite to the front, 

 behind the oral aperture. Polygordius and Protodrilus thus approach the Terebellidce 

 in the arrangement of their fore-gut. 



The genus Sternaspis, which possesses a strongly muscular pharynx, is distin- 

 guished by the fact that the seven anterior segments of the body can be invaginated. 



Glands entering various parts of the pharyngeal apparatus have been observed in 

 many Polychceta. 



In the Echiuridce the fore -gut is, relatively speaking, little dis- 

 tinguished from the mid-gut, and it even takes part in the formation 

 of the loops which the intestinal canal makes in the body cavity. 

 Three divisions are distinguished in it from before backward -the 

 pharynx, the oesophagus, and the crop. It is the oesophagus in which 

 the muscular layer is specially strongly developed. It is not certain 

 whether any part of the fore-gut can be protruded. Food is in any 

 case seized by means of the prostomium (proboscis) and conducted to 

 the mouth along its ventral groove. 



The Myzostomidce possess a pharyngeal apparatus, constructed on 

 the plan of that of the Rhynchobdellidce among the Hirudinea. At the 

 free end of the pharynx there are tentacle-like processes. 



In the Prosopygia the fore-gut is in general very short and not 

 strikingly developed. This is evidently in keeping with the manner 

 of taking food of these mostly attached animals ; their feeding is 

 chiefly accomplished by the help of special outer appendages of the 

 head (tentacles, arms). (In a similar way we found that in the 

 Chcetopoda inhabiting tubes or living in mud and provided with a 

 crown of tentacles or a prostomium, the pharyngeal apparatus is far 

 less developed than in the other forms.) Among the Sipunculacea a 

 well-developed oesophageal bulb is present in the Priapulidce only ; its 

 inner cuticle forms numerous teeth projecting into the lumen. The 

 musculature is very powerful, and consists principally of circular and 

 radial muscles. In the Phoronidce, Bryozoa, and Bmcliiopoda the fore- 

 gut is represented by the connective piece between mouth and intestine 

 surrounded by a muscular layer, and is not very well marked ; this 

 is generally described as the oesophagus. 



In the Rotatoria (Fig. 161, p. 245) the mouth leads first into a 

 narrow ciliated buccal cavity (oesophagus), in connection with which a 

 muscular layer is only rarely found. The buccal cavity is followed by 

 the distinctly separate cesophageal bulb or pharynx, which is provided 

 with a chitinous masticatory apparatus and strong musculature for 

 moving it. The masticatory apparatus consists of a middle part 

 (incus) and 2 lateral parts (mallei), each of which again consists of 

 2 pieces connected by a hinge (uncus and manubrium). The buccal 

 cavity and the pharynx together ought to be considered as the fore- 

 gut. In the pharynx of various Rotatoria salivary glands enter. 



The fore-gut of the species DinopUlus (Fig. 162, p. 246), by its 

 ventral muscular appendage whose hollow anterior end enters the 



