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XLV] development, it penetrates into the visceral cavity of certain snails (Physa alexandrina, P. micropleura), and in these develops and multiplies parthenogenically. In about two months, having attained the cercaria stage, the cercariæ escape from the snail, swim around in the water, and finally encyst themselves on plants or other objects. The final host (cattle, etc.) is attained either through drinking-water or pasture.

Geographical distribution.—Information is as yet very scanty, but there is reason to believe that W. watsoni is by no means uncommon in certain parts of northern Nigeria, where it gives rise to serious intestinal trouble, especially in children. A patient who had lived there for some time told me that on one occasion, being seized with violent diarrhœa, he passed about a pint of material containing innumerable moving bodies which he described as resembling the heads of tadpoles, doubtless specimens of W. watsoni.

Treatment.—As for adult tapeworms.

Synonyms.—Amphistomum hominis; Gastrodiscus hominis (Lewis and McConnell, 1876).

History.—This parasite was described by Lewis and McConnell in 1876 from two sets of specimens, the first procured from O'Brien and Curran, who found them in the vicinity of the ileo-colic valve at the post-mortem of an Assamese in Gowhatty; the second belonging to the Pathological Museum of the Calcutta Medical College, and presented in 1857 by Simpson, who found them in the cæcum and ascending colon of an Indian who died from cholera in the Tirhoot jail hospital. G. hominis is now found to be a much more common parasite of man than was formerly supposed. A study of serial sections has convinced Leiper of the necessity of removing it from the genus Gastrodiscus on the following grounds: (1) the presence of a large imminent genital papilla in place of the genital atrium of gastrodiscus; (2) testes tandem; (3) genital orifice on the neck, not on