FREE-LIVING FRESH-WATER NEMATODES 83 



as wide as the corresponding portion of the body. It is connected with 

 the seminal vesicle by a narrow portion. The seminal vesicle is elon- 

 gated, about half as wide as the body, and extends to a point about as 

 far behind the neck as the base of the neck is from the anterior ex- 

 tremity. From this point the two nearly equal testicles extend in oppo- 

 site directions, and end blind, one not far behind the base of the neck, 

 and the other not far from the middle of the body. These possess the 

 peculiarity of being slightly swollen at their proximal ends just where 

 they join the vesicle. These swellings appear to constitute veritable 

 cavities of small size. That region of the body corresponding to the 

 ejaculatory duct is traversed by oblique striae, which, however, are ar- 

 ranged at right angles to the direction of such oblique striations as 

 are found in other genera, and it is probable that they are connected with 

 the duct itself, and are not muscles of the character which usually give 

 rise to these oblique striations on the males of other genera. The two 

 equal, arcuate slender spicula appear to be of rather uniform diameter 

 when viewed laterally, and are one and one-half times as long as the 

 anal body-diameter. Their proximal ends are cephalated by contrac- 

 tion. They are accompanied by accessory pieces two-fifths as long as 

 the spicula themselves, and arranged parallel to the distal portions of 

 the spicula. 



Habitat: Mud, about the bases of aquatic plants, Potomac river, 

 D. C. 



MESOMERMIS, Dady. 

 Fig. 18, Plate VII. Fig. 24, Plate VIII. 



55 

 - ,, .8 6.3 ii. -M- 96. 



27. Mesomermis virgimana, n.sp. 1.8 mm. 



1.3 2. 1.8 2.3 2.2 



The rather thick, transparent, colorless layers of the naked cuticle 

 are destitute of transverse striations. There are minute longitudinal 

 striations throughout the body. These are interrupted on the lateral 

 lines, where there is a distinct wing. The conoid neck becomes convex- 

 conoid toward the lip region, which is not set off in any way. There 

 are no cephalic setae, and there is no distinct pharynx. The mouth 

 pore is very minute, and is a little toward the ventral side of the middle 

 of the front of the head. The cuticle has about the same thickness on 

 the head as elsewhere, being only a trifle thicker. The cuticle is pene- 

 trated on the head by a number of innervations. These end in minute 

 depressions on the surface of the head. Near the mouth opening there 

 is one of these depressions on the dorsal side, and apparently a sim- 

 ilar one on the ventral side, while nearer the outer margin of the head 

 there are two ventrally submedian and two dorsally submedian similar 

 depressions. Pores occur also here and there on the body as well as 

 on the neck. There are no eye-spots. The lateral organs present the 



