SEXUAL ORGANS (8.5.449)147 



very difficult of observation. They are most easily detected when viewed 

 dorso-ventrally, and then appear as refractive oblique elements leading 

 from the surface of the head inward and backward through the trans- 

 parent cuticle, as shown for instance in the cases of subtenuis and regius 

 (p. 167 and 140). They can seldom be followed more than a short dis- 

 tance inward, and their ultimate internal connections are unknown. A 

 nerve-ending is nearly always to be seen in the cuticle immediately behind 

 each amphid. 



No Eyes 



Mononchs have no definite organs of vision. 

 Female Sexual Organs 



Organs Mostly Double. Eggs. Ovaries and Ova. From the slightly 

 elevated and rather small vulva, the prominent refractive vagina leads 

 inward at right angles to the ventral surface about one-third the distance 

 across the body. Though comparatively small in size, the vulva is usually 

 easily located on account of the refractive nature of the walls of the 

 vagina. In nine-tenths of the species, the internal female organs are 

 double, and symmetrically reflexed, though in some cases the posterior 

 branch is somewhat smaller than the anterior. In the exceptional species 

 the single ovary is also reflexed (fig. 14). The ovaries occupy relatively 

 less space than is usual in nemas less than one-fourth of the length of 

 the body. Owing to the comparatively great length of the neck, the vulva 

 is usually located somewhat behind the middle of the body even when 

 the sexual organs are double and symmetrical, and may occur as far 

 back as the junction of the third and final fourths. Each of the two uteri is 

 about twice as long as the body is wide, that is to say, of a size to receive 

 one or two eggs only. These latter are nearly always smooth, thin-shelled, 

 ellipsoidal or elongated in contour, and appear about twice as long as the 

 body is wide, though they are sometimes somewhat shorter, and more 

 rarely longer. Only in a single species are the shells known to be sculp- 

 tured. The shells are thick in obliquus. In all the species examined by the 

 writer, the eggs are deposited before segmentation begins, and this is 

 presumably true of the great majority, if not of all the species. The 

 reflexed ovaries extend one-half to three-fourths the distance back to the 

 vulva and contain a score or so of ova, which near the blind ends are 

 packed in several rows ova that by increase in size come, each one in 

 turn, to occupy the whole of the width of the organ in its proximal half 

 near the flexure. The ovaries are rather broad, and taper relatively little. 



Syngonism. A considerable number of the mononchs are syngonic, 

 and it is probable nearly all of them are so, since the males, if found at all, 

 are nearly always rare. Only on a single occasion, so far as records go, 

 have males been found to be as common as the females. Of most species 



