The mouth parts exhibit several interesting details of structure that are unfortunately unnoted either in the description or in the figure of the corresponding species P. caucasica. The two large fleshy lips of P. mordens bear in addition to the pair of touch papillae and the horny "external tooth" common to these forms, a pair of cuticular knobs that jut out and lie in apposition to one another at the outer and posterior limits of the transverse fissure
of the mouth, on either side (Fig. 2).
Further, the cuticular fold known as the "inner tooth," lying in the median line on the inner aspect of the lip and overhung by the horny external tooth, presents a sharp-cutting edge towards the lumen of the mouth, and projects forwards, tapering to end anteriorly in a single lancet-like tip.
Both lips are bound together posteriorly by a thick encircling cuticular band, where the cuticle leaves the surface of the anterior part of the body to form the praeputial-like fold characteristic of the genus. At a distance equal to three times the transverse diameter of this band, measuring backwards therefrom, are to be found the cervical papillae.
The alimentary canal shows the usual divisions into oesophagus, intestine, and rectum. The oesophagus, in the specimen figured, measured exactly one-sixth of the body length. It shows transverse muscular striations, and becomes only very gradually more broadened towards its intestinal opening. The chyle intestine commences with a lumen only slightly greater than the external circumference of the terminal part of the oesophagus and gradually becomes narrowed during its whole course to the short rectum, at its junction with which one finds the large unicellular masses that have been noted at this situation in many other groups of nematodes (Fig. 1).
The anus lies on the ventral surface at a distance of
