OBSERVATIONS ON THE MORPHOLOGY 

 AND PHYSIOLOGY OF NEMAS 



Including notes on new species 



CONTRIBUTIONS TO A SCIENCE OF NEMATOLOGY XXIII 

 BY N. A. COBB 



1. A NEW SUBGENTJS OF RHABDITIS 



There is a group of slender-tailed amphigonic rhabdites having 

 lips and pharynx as shown in Fig. 1, the males of which have weakly 

 developed bursas. Such rhabdites have been described from time 

 to time but no author seems to have had adequate material for a 

 completely satisfactory description. Having examined living speci- 

 mens of both sexes of a new species of this group I took the occa- 

 sion to prepare a fuller description of it, and propose it as the type 

 of Rhabditella, a new subgenus of the genus RhabditJs Dujardin. 



Rhabditis (Rhabditella) leptura n. sp . 



Thin layers of the transparent, colorless, naked cuticle are traversed by 

 excessively fine, plain, transverse striae, resolvable only with the highest 

 powers. Longitudinal striations, due to the attachment of the musculature, 

 are visible in most regions of the body. No deirids have been observed. 

 The neck is very slightly conoid. The cross section of the pharynx is 

 roundish-triangular; yet the almost imperceptibly sigmoid pharynx is nearly 

 equidiametral throughout, though anteriorly the walls are a trifle more 

 strongly refractive. The glottis is a trifle oblique, but otherwise fairly typical. 

 The oesophagus presents a median, fairly prominent, ellip- 

 soidal swelling, or bulb, two-thirds as wide as the middle of the 

 neck, and a somewhat ellipsoidal, or obscurely pyriform pos- 

 terior bulb two-thirds as wide as the base of the neck, both 

 swellings of approximately the same diameter. The median 

 swelling presents an elongated, obscure but rather large, 

 valvular apparatus, while the cardiac bulb presents a rather 

 strongly refractive, somewhat three-fold, striated valvular ap- 

 paratus, located a little in front of the middle of the bulb. At 

 the nerve-ring the oesophagus is one-third, and in front of the 

 cardiac bulb about one-fourth, as wide as the corresponding 

 portion of the neck. There is a distinct cardiac collum con- 

 stituting a rather broad constriction, so that the anterior 

 portion of the intestine through a distance nearly equal to one ..... _____ 

 body-width enlarges from about one-third to five-sixths as Fig L Front and 

 wide as the body. This appearance, however, is somewhat ^f^^fj^l 

 variable. The nerve-ring surrounds the oesophagus obliquely, hptwa. Thebegin- 

 The intestine, the lining of which is somewhat refractive, is ^Vlhown 15 P the 

 made up of cells of such size that probably only about two lower illustration. 

 are presented in each cross section; these cells contain granules 

 of variable size, which are not strongly birefringent. With crossed nicols 

 there is no suggestion of a St. Andrew's cross; not at all like the strong 

 birefringence of R. monohystera. The posterior Up of the anus is very slightly 

 raised. The rectum, whose lining is only slightly refractive, is one and one- 

 Reprinted from the JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES, Vol. 19, 

 No. 13, July 19, 1929. 



