THE MONONCHS 



of the pharynx, indicating a division of the wall into anterior and posterior 

 elements. Sometimes this pharyngeal suture is rather prominent. 



Jaw Muscles. The pharyngeal muscles of various species of mononchs 

 have been observed, figured and commented upon by one or two investi- 

 gators, but only in a vague way. Much remains to be learned concerning 

 them. The following incomplete observations have been made in the 

 course of these investigations. 



Under suitable conditions, and especially in some species, long, slen- 

 der muscles may be seen passing from the lip region backward and out- 

 ward, so that their proximal attachment is to the body-wall a short 

 distance behind the pharynx. These muscles are the flexor muscles of 



X750 



FIG. 9. Side view of 

 the head of M. regius. 

 The lips and their ap- 

 pendages are well shown. 

 The flaps (lam. Ib.) are 

 the same organs so well 

 seen in figure 4. The 

 amphid (amph.) extends 

 to the bottom of the 

 pharynx and beyond. The 

 labial muscles (msc.) are 

 so attached as to pull the 

 lips both inward and out- 

 ward about the stiff exter- 

 nal ring as a fulcrum. 

 Traces of this ring are 



margin of the anterior 

 part of the head. Com- 

 ing up from the interior 

 of the oesophagus toward 

 the right is seen a light- 

 colored duct; this empties 

 into the pharynx at its 

 base. In this way appar- 

 ently the secretion of the 

 oesophageal glands has a 

 direct passage to the 

 throat 



the lips. It is certain that each lip, probably each pair of adjacent lips, is 

 connected with a muscle whose function is to pull the lip toward the body 

 axis about a fulcrum near the surface of the head. These muscles, then, 

 shut the mouth. It seems likely that the elasticity of the various parts 

 composing the frame-work of the lips and pharynx may play some part 

 in mastication and deglutition, and act in opposition to some of the mus- 

 cular elements of the pharynx. The extent to which a mononch can 

 throw its jaws open is shown in the sketch, figure 1, made from a pre- 

 served specimen. This act is accomplished by the aid of a second similar 

 set of muscles acting on the outside of the same fulcra. It is unlikely 



