BY VERA A. IRWIN-SMITH. 775 



ridge is more definite in outline and appears to be in contact 

 with the alimentary canal throughout its length. In the head, 

 tlie space between the pharynx and the body-wall is almost com- 

 pletely filled out with a loose, hypodermal tissue (Text-figs. 9, 10, 

 hyp ), but, in the trunk, a definite ccelome is present, between 

 the enteric canal and the body-wall. In the young worm, this 

 space is relatively large, and extends uninterruptedly from the 

 neck to the tail-region, where it is again filled out with proto- 

 plasmic tissue But, in the adult, it is extensive only in the 

 region of the oesophagus (Text-fig.5, coeL). Further back, it 

 becomes almost completely occluded by the growth of the genital 

 organs and intestine. The enteric canal is a straight tube 

 running through the length of the body, from the mouth, at 

 the anterior end, to the anus near the posterior end. By varia- 

 tions in its width, and in the thickness of its walls, it is dis- 

 tinguishable into pharynx, oesophagus, intestine, and rectum. 



The three-rayed mouth-opening (Text-fig.ll) leads, through a 

 very short and narrow passage, into a rounded bulb with thick, 

 muscular walls, the anterior pharyngeal bulb ('J'ext-fig.9, a.ph.). 

 Its narrow cavity is rayed in cross-section, and is lined by cuticle 

 {c.p.) which, everywhere thick, is thickest in the anterior portion, 

 where the lumen is slightly larger than it is further back. Its 

 walls are composed of a complicated system of circ^ular, longi- 

 tudinal, and radial muscle fibres. Bands of muscle-fibres (Text- 

 fig. 10, y^/'.) attach its anterior end to the cuticle of the body- 

 wall dorso- and veiitro-laterally, and further back, towards its 

 posterior end, there appear to be finer strands of fibrils running 

 forward to attach it laterally. The anterior pharyngeal bulb 

 extends through a little more than one-third of the length of the 

 head, and is followed immediately by a second rounded swelling 

 of equal length and width, the posterior pharyngeal bulb, the 

 walls of which are composed of a less complicated system of 

 radial muscle-fibres. Its lumen is still very nari-ow, and is lined 

 with cuticle (Text-fig. 9, p.ph.). It is divided by a well-marked 

 constriction from the oesophagus, which is slightly swollen in 

 the head-region to form a third, much smaller bulb (PI. xliv., a.o.). 

 This, however, diff'ers from the pharyngeal bulbs in having non- 



