FREE-LIVING FRESH-WATER NEMATODES 45 



the neck and body there are a few hairs arranged at right angles to the 

 surface. These generally have a length equal to the width of two to three 

 annules of the cuticle. The cylindroid neck ends in a somewhat truncated 

 head, which is not set off in any way. On the outer margin of the head at 

 the base of the lips there is a circlet of ten widely spreading, straight, taper- 

 ing cephalic setae, two of somewhat unequal size on each submedian line, 

 and one on each lateral line. The longest of these setae are a little more 

 than half as long as the head is wide. For two-thirds of their length they 

 are finger-shaped; the remaining third is a much narrower bristle. The 

 very thin lips are arched over the prismoid pharynx, which is nearly as deep 

 as the head is wide, and about three-fifths as wide as the head. It attains 

 its full width immediately behind the lips, and continues to have the same 

 width to the end, so that the bottom of the pharynx, though not even, ex- 

 tends across the base of the head approximately at right angles to the body 

 axis. Where the lumen of the oesophagus joins the pharynx there is, how- 

 ever, a slight backward extension of the pharyngeal cavity. There are no 

 eye-spots. The amphids occur in the form of somewhat elongated trans- 

 verse markings placed transversely on the neck somewhat farther behind 

 the base of the pharynx than this latter is behind the anterior extremity. 

 Each amphid has a length about one-third as great as the corresponding 

 width of the neck, and is about half as wide as long. Behind each amphid, 

 at a distance equal to the width of two to three annules of the cuticle, there 

 is a short seta. The oesophagus receives the base of the pharynx, and is 

 at once nearly three-fourths as wide as the head. It narrows very slightly 

 in diameter as it passes backward, so that where it passes through the nerve- 

 ring it is about two-thirds as wide as the neck. It continues to have prac- 

 tically the same diameter to near the end, where it is two-thirds as wide as 

 the base of the neck. Immediately in front of the intestine there is a small 

 segment of the oesophagus which is set off by a constriction. This 

 portion is somewhat spheroidal in form. The lining of the oesophagus is a 

 distinct feature throughout its length, and comes into view in the optical 

 section as a single refractive line. This line is nowhere materially altered. 

 There is no distinct cardia, unless the above mentioned spheroidal segment 

 of the oesophagus may be so considered. The rather thick walled intestine, 

 which is set off from the oesophagus by a distinct constriction, becomes at 

 once about two-thirds as wide as the body, and is composed of cells of such 

 a size that probably about four are required to build a circumference. These 

 cells contain numerous granules of rather uniform size, which are not dis- 

 posed so as to give rise to a tessellation. From the somewhat continuous 

 anus the rectum, which is about as long as the anal body diameter, extends 

 inward and forward. The tail end begins to taper from some distance in 

 front of the anus, and tapers regularly thereafter throughout the anterior 

 portion of the tail. The posterior portion tapers very slightly, and has a 

 diameter one to two times as great as the width of one of the annules of 

 the cuticle, measured near the anus. Though the terminus has considerable 



