FREE-LIVING FRESH-WATER NF.MATODES 49 



solvable. In the lumen of the pharynx at a point removed from the 

 anterior extremity a distance a little greater than the radius of the 

 head, there is a minute inward-pointing dorsal tooth, having a length 

 about equal to the width of one of the annules of the cuticle. This 

 and other matters prove that the pharynx, although not readily dis- 

 tinguished, extends backward a distance about equal to the width of 

 the head. In some specimens it is possible to see a distinct transverse 

 fold in the lining of the oesophageal tube. This is located at a dis- 

 tance from the anterior extremity about equal to the corresponding 

 diameter of the head, and undoubtedly indicates the posterior lim- 

 its of the pharynx. It is possible that the tooth just mentioned may be con- 

 nected with internal glandular structures in the oesophagus, as the interior 

 of the dorsal segment of the oesophagus at this point is usually more or 

 less different in structure from the other portions and does not seem to be 

 made up entirely of muscular fibers. The oesophagus is separated from the 

 intestine by a flattish, pseudo-bulb. The bulb is separated from the oesopha- 

 gus on one side and the intestine on the other by deep and distinct constric- 

 tions. In the anterior constriction there are at least two granular, elongated 

 cells of considerable size. The nerve-ring surrounds the oesophagus rather 

 squarely. Nothing definite is known concerning the renette or the excretory 

 pore. From the inconspicuous vulva, the vagina leads inward at right 

 angles to the ventral surface fully half way across the body, where it joins 

 the two symmetrically-placed uteri. The reflexed ovaries reach about half 

 way back to the vulva, and contain a dozen to twenty developing ova ar- 

 ranged somewhat irregularly. Both in front of and behind the vulva there 

 are unicellular glands, having a diameter about one-sixth as great as that 

 of the body. 



50 



.7 6.8 19.3 -M- 82.8 



2.4 mm. 



2.1 3.2 3.9 4.8 4.1 



The tail of the male is like that of the female except that the anus 

 is slightly raised. In front of the anus there is a ventral row of about 

 twenty innervated supplementary organs, reaching to near the head. 

 The distance between two consecutive organs is about equal to the ra- 

 dius of the body. Each of these appears to consist of a nerve-ending 

 which penetrates the cuticle and forms a papilla, around which there is 

 an almost imperceptible elevation having a width about equal to two of 

 the annules of the cuticle. The visibility of this small organ is quite as 

 much due to the alteration in the body wall and subcuticle as to that in 

 the cuticle. There are no supplementary setae or papillae either in 

 front of the anus or behind it. The two equal, slightly arcuate, uni- 

 formly tapering, acute spicula are about one and one-fourth times as 

 long as the anal body diameter. Their proximal ends are not cephal- 

 ated, though the wall of the cuticle is very slightly thickened at that 

 point. The spicula taper regularly from the proximal ends to the rather 



