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Rh The parasite (Figs. 146-8).—The female is reputed to attain in some instances enormous dimensions; it is probable, however, that worms of 5 or 6 ft. in length owe their size to errors of observation, two worms, or their fragments, having been regarded as one. According to Ewart, in forty carefully measured specimens the smallest was about 32·5 cm., the largest 1 m. 20 cm. in length; 90 cm. is probably an average length. The diameter of the worm is about 1·5 to

Fig. 146.—Dracunculus medinensis (reduced).

1·7 mm. The body is cylindrical, milky-white, smooth, and without markings. The tip of the tail comes to a point and is abruptly bent, thus forming a sort of blunted hook, perhaps functioning as a "holdfast." The head end is rounded off, terminating in what is known as the cephalic shield. The mouth is triangular, very small, and surrounded by six papillæ—two large and four small The alimentary canal is relatively small, being compressed and thrust to one side by the uterus; in the mature worm it is probably cæcal, for it has not been traced to an anus. Nearly the whole of the worm is occupied by the uterus, which is packed from end to end with coiled-up embryos. The vagina also may be lacking. According to Looss, the uterine tubes (he states, contrary to Leuckart, that there are two) open into the posterior part of the œsophagus by a common duct, the œsophagus prolapsing through the mouth at the time of parturition and being subsequently withdrawn. Leiper, however, has shown that the worm discharges its young by a prolapse of the uterus as described by me, and that the extrusion does not occur through the mouth, as suggested by Looss and myself, but by a rupture just outside the circumoral ring of papillæ, possibly the vagina.

Nothing definite is known of the male worm. According to Polak, the Persians have long known the male to be a smaller worm, 7-10 cm. long. They stated that at times as many as twenty of these small worms might be found coiled round a female specimen. Charles described a shorter (4 cm.) worm, regarding it as the male, which he found