FREE-LIVING FRESH-WATER NEMATODES 41 



RHABDOLAIMUS, de Man, 1880. 

 Fig. 2, Plate II. 



28 



2. Rhabdolaimus minor, n.sp. 4 ' 6 * 5 ' ^ <5I> 77 ' 5 2 8 mm 



2.4 37 3-8 4- 2. 



The thin layers of the transparent, naked, colorless cuticle appear to be 

 destitute of any but very fine transverse striations, most clearly visible near the 

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

 way. There are no cephalic setae. Careful focussing appears to indicate on 

 the outer margin of the head the presence of almost invisible papilla-like or- 

 gans which may perhaps be representatives of cephalic setae. There are no 

 lips. The amphids are located at a distance from the anterior extremity 

 about three times as great as the width of the lip-region, and a little more 

 than twice as great as the width of the head near where they occur. Seen 

 in dorso-ventral view they have the appearance of obscure openings from 

 which there leads inward and backward slight refractive elements which 

 soon become indefinite. Immediately behind the mouth opening there is at 

 least one obscure refractive element of small size, apparently very much as 

 figured by Dr. de Man in his description of the type species. The tubular 

 pharynx is long and slender, extending backward for a considerable distance 

 behind the amphids. Its total length is probably a little less than one-third 

 the distance to the nerve-ring, though the limits are not definite in the speci- 

 mens so far examined. The oesophagus is at first about three-fourths as 

 wide as the head and continues to have this diameter, or a slightly greater 

 diameter, until near the end, where it expands to form the pyriform cardiac 

 bulb which contains an obscure valvular apparatus. This bulb is three- 

 fourths as wide as the base of the neck. The lining of the oesophagus may 

 be faintly seen throughout its length. The rather thin-walled intestine which 

 is separated from the oesophagus by a slight constriction becomes at once 

 three-fourths as wide as the body. It appears to be composed of cells of 

 such size that probably only four to six are required to build a circumfer- 

 ence. From the nearly continuous anus, the rectum, which is somewhat 

 longer than the anal body diameter, extends inward and forward. The tail 

 begins to taper from a little in front of the anus and tapers regularly to 

 the terminus which is armed with a striking, elongated, unarmed, slightly 

 tapering, acute spinneret. Where the tail joins the spinneret the diameter is 

 about one-fifth as great as at the anus. There is a sudden and very slight 

 diminution of diameter of the terminus where it joins the spinneret. From 

 the inconspicuous vulva, the vagina leads inward and forward. The sym- 

 metrically reflexed ovaries reach about half way back to the vulva. The 

 thin-shelled, smooth eggs are relatively large and elongated and have 

 been seen in the uterus one at a time. They are about four to five 

 times as long as the body is wide and about one-fifth as wide as long. 

 They appear to be deposited before segmentation begins. 



Habitat: Mud, Beach pool, Pine Point, Douglas Lake, Michigan. 

 Sublimate to balsam. 



