FREE-LIVING FRESH- WATER NEMATODES 75 



These occupy a space a little more than the width of one of the annules of 

 the cuticle, but sometimes one of these lines is more prominent than the 

 other. The conoid neck ends in a rounded head, which is not set off in any 

 way. There are no cephalic setae. There does not appear to be any distinct 

 pharynx. The lining of the oesophagus is slightly modified back twice as 

 far as the posterior margins of the amphids, and very likely this portion of 

 the tube may be regarded as a narrow rudimentary pharynx. Twice as far 

 from the anterior extremity as the base .of this supposed pharynx the 

 oesophagus is distinctly interrupted by a break in the musculature, although 

 there is no change in size, and just behind this break there are three distinct, 

 elongated nuclei, one in each segment of the oesophagus. These appear- 

 ances are reminiscent of the arrangement in Plectus, to which Aphanolaimus 

 is doubtless related. There do not appear to be any distinct lips, though 

 possibly there may be three exceedingly minute, well amalgamated, flattish 

 ones. Although at first glance the amphids appear to be circular, they are 

 really spiral in form. They are about one-fifth as wide as the corresponding 

 portion of the neck. Their distance from the anterior extremity is about 

 equal to the diameter of the head; or in other words, their centers are re- 

 moved from the anterior extremity a distance about twice as great as their 

 diameter. The amphids appear to be slightly larger in the male than in the 

 female. There are no eye-spots. The oesophagus begins at the base of the 

 above described pharynx, as a tube about half as wide as the corresponding 

 portion of the neck. It widens very gradually, so that where it passes 

 through the nerve-ring it is nearly one-third as wide as the corresponding 

 portion of the neck. At the middle, nearly opposite the nerve-ring, there 

 is an almost imperceptible increase in diameter, indicative of a deteriorated 

 median swelling. Finally, it expands into the narrowly pyriform cardiac 

 swelling destitute of any distinct valvular apparatus. This swelling is half 

 to two-thirds as wide as the base of the neck. The lining of the oesophagus 

 is a distinct feature throughout its length. There is no distinct cardia. The 

 intestine, which is at first only one-fifth as wide as the base of the neck, 

 joins the middle of the posterior surface of the cardiac swelling. It is 

 moderately thick-walled, and gradually becomes about two-thirds as wide as 

 the body. It appears to be made up of cells of such a size that few, prob- 

 ably two or three, or possibly four, are required to build a circumference. 

 The body tapers gradually from a long distance in front of the anus. This 

 latter is very slightly raised, more particularly on the anterior margin. From 

 it the rectum, which is about as long as the anal body diameter, extends in- 

 ward and forward. The tail is conoid in the anterior three-fourths. The 

 posterior fourth is cylindrical and has a diameter nearly one-third as great 

 as that of the base of the tail. It ends in a rounded, unarmed spinneret, bear- 

 ing an apiculum. The lateral fields appear to be about one-third as wide as 

 the body. The nerve-ring surrounds the oesophagus somewhat obliquely. 

 There appears to be a small renette cell opposite the anterior portion of 

 tire intestine, but the position of the excretory pore has not been discovered. 



