390 



ASCAROPHIS HELIX 



on the external form of an ordinary multiple-threaded screw. Here, in the mid- 

 dle, the contour of the body has become very coarsely and very pronouncedly 

 compound-crenate. The more pronounced striae come to subtend twelve 

 minor ones (Fig. 3). Finally near the tail end, the more pronounced striae 

 subtend six minor ones (Fig. 3) ; this is near where the body is bluntly rounded 

 off, in a hemispherical-conoid manner, in the course of a distance equal to 

 about one and one-half body widths (Fig. 1). At first sight the deceptive 

 appearance of the cuticle toward the posterior end of the nema suggests 

 moulting, and consequent wrinkling of the cuticle. Longitudinal "striations," 

 about 2 microns apart, due to the attachment of the mus- 

 culature, are visible in most regions of the body. Posteriorly 

 these longitudinal "striae" are still slightly oblique, and 

 this slight obliquity extends practically to the terminus. 

 There are no cuticular wings. With the nema in profile 

 the lateral chords appear about one-seventh as wide as the 

 body. 



The groove-like unarmed " vestibule" is very simple and 

 shallow, about as deep as the height of the two prominent, 

 lateral, forward-pointing, conical labial projections (Fig. 1, 

 proj #>). The vestibule leads through the slit-like mouth 

 opening into a long, uniform, tubular pharynx, extending 

 more than halfway to the nerve-ring. The pharynx is a 

 marked feature of the front end, though it is so transparent 

 and dimly refractive that it might, perhaps, under some 

 circumstances, rather easily be overlooked (Fig. 1). Van 

 Beneden seems to have figured the pharynx; Nicoll not, or 

 at least not definitely. The mouth seems to lead into a 

 minute pharyngeal or vestibular cavity, not very much wider 

 than the amphids, perhaps six to eight microns wide, a 

 little longer dorso-ventrally than transversely. The 

 median axil between the two lips is not sharp and distinct. 

 The inner surfaces of the conical labial projections are 

 not uniformly rounded and striated, like the outer sur- 

 faces, for, near the middle, in their inner lateral lines 

 or fields there are refractive longitudinal elements ex- 

 tending from the tips back to the mouth opening. It 

 seems quite certain that there is an axial element ex- 

 tending to the apex of each of these conical projections, 

 and when this is viewed in optical section, as one focuses 

 from front to back, the appearances give rise to the opinion 

 that there is a single innervation to each conical pro- 

 jection. One sees no evidence of radial musculature 

 round the vestibule. There are no eyespots; and there is no pigment near 

 the head, or elsewhere in the nema. 



Returning now to the profile and dorsal views of the head; four to five 

 microns behind the tips of the two cephalic projections, exceedingly minute 

 openings in the lateral region indicate the external amphids. As viewed 

 dorso-ventrally, the anterior part of the walls of the pharynx, without diminish- 

 ing much in thickness, bend together and nearly meet near the base of the 

 vestibule, thus giving rise to the narrow mouth opening; in this anterior 

 portion of the pharynx, the transverse striation is less apparent. 



Behind the pharynx the oesophagus is a little less than one-third, at the 

 nerve-ring about one-fourth, twice as far back as the nerve-ring a little less 



Fig. 2. Camera 

 lucida drawing of 

 an oblique view of 

 the eight-fold heli- 

 coid striae of As- 

 carophis helix, at 

 lat. 23, near the 

 beginning of the 

 intestine. The an- 

 astomosing occurs 

 opposite the lateral 

 chords. 



