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Rh apparently the parasite was introduced by a man who had served as a soldier in the Boer War. As this shows that the conditions (intermediary host, etc.) are present, the spread of bilharzia disease in Australia may be anticipated.

Etiology.—Schistosomum hæmatobium (Figs. 129, 130, 131) is a bisexual trematode belonging to the family Schistosomidæ. The male is white, cylindroid, 11 to 15 mm. in length by 1 mm. in breadth. It possesses an oral and a ventral sucker of about equal size and placed close together. The cylindrical appearance of the worm is produced by the ventral infolding of the two sides of what would otherwise be a flat body. By this infolding a gynæcophoric canal is formed, in which the female can be partially enclosed. The outer surface of the body is closely beset with small cuticular prominences. The female is rather darker in colour than the male, considerably longer (20 mm.), more filiform, her middle being usually enclosed in the gynæcophoric canal referred to, whilst her anterior and posterior portions remain free. The genital openings of the sexes face each other, and are placed immediately posterior to the ventral sucker. The sexes live apart while young, but on reaching maturity the female enters the gynæcophoric canal of the male.

These parasites are found in the blood of the portal vein, in its mesenteric and splenic branches, and in the vesical, uterine, and hæmorrhoidal veins; they have also been found in the vena cava. Sonsino considers that, if searched for, they would probably be found elsewhere in the circulation. Their numbers vary considerably. Sonsino reports finding in one case forty; in another case Kartulis found 300 in the portal vein and its branches. Looss has seen the submucous tissue of the bladder so rich in worms that a pair could be found in every area of half a centimetre square.

The ovum.—On microscopical examination the uterus of the female bilharzia is found to be stuffed with ova of a