FREE-LIVING NEMATODES 5OI 



6 1 (60) Form of cavity various, closed in front, amphids opposite it. . 62 



62 (63) Lateral organs or amphids inconspicuous Trilobus Bastian. 



Fresh-water genus of which about half a dozen species are known. Known to feed upon 

 diatoms in one case and upon rotifers hi another. Hermaphroditism occurs. 



Representative species Trilobus longus (Leidy) 1851. 



19. 



....... 



89. 

 . . 



> 12mm. 



The lips bear papillae but their number is not 



S> a 1.3 8. if. -M- .??.-....> ,2mm. known. The intestine frequently contains diatoms 



in large numbers, indicating that these are a common 



source of nourishment of this species. The longitudinal fields are distinctly developed, and 

 about one-fourth as wide as the body. From the slightly elevated vulva the vagina leads in- 

 ward at right angles to the ventral surface fully half way across the body. The reflexed 

 ovaries pass about two-thirds of the way back to the vulva. Two or three eggs may occur in 

 each uterus at one tune. These are somewhat ellipsoidal and thin shelled, being about two- 

 thirds as long as the body is wide and about two-thirds as wide as long. The eggs appear to 

 pass through at least the early stages of segmentation before being deposited. The walls of 

 the vagina present the peculiarity of being very thick, and composed of six to seven con- 

 centric layers so that the organ is considerably broader than it is deep. Its internal wall 

 presents the peculiarity of staining strongly with carmine. 



Trilobus longus, the only American fresh-water nematode outside the Mermithidae that had 

 been adequately characterized previous to the inception of this chapter, was described by the 

 famous Philadelphia naturalist, Dr. Joseph Leidy, in 1851. At that tune extremely little was 

 known about the free-living fresh-water nematodes, and no one dreamed of their vast number 

 and variety. The peculiar male supplementary organs of Trilobus did not fail to attract atten- 

 tion, and it is owing to this fact that Leidy's name is associated with the striking species 

 selected as a representative of the genus. 



Habitat: Mud about the bases of aquatic plants, in pools, ditches, rivers, and lakes through- 

 out the country. 



FIG. 806. Trilobus longus. 



I, male; II, head, lateral view; III, head, lateral view; IV, head, ventral view; V, anterior supple- 

 mentary organ; VI, posterior supplementary organ; VII, two supplementary organs from an exceptional 

 female. 



a, lateral seta; b, papilla; c, submedian seta; d, pharynx; e, lateral organ; /, tooth; g, tooth; h, esoph- 

 agus; i, nerve-ring; j, excretory pore; k, body muscles; /, glandular (?) organs; m, intestine; n, blind 

 end anterior testicle; o, testicle; p, junction of testicles; q, blind-end posterior testicle; r , vas deferens; 

 s, nerve of supplementary organ; /, cavity of supplementary organ; u, left spiculum; v, accessory piece; 

 w, the three caudal glands; x, anus; y, terminus; z, apex of supplementary organ. (After Cobb.) 



