The means by which infection is brought about are still uncertain; we only know that the miracidia (fig. 175) enclosed in the discharged eggs do not hatch if the eggs remain in the urine, but after cooling perish. As soon, however, as the urine is diluted with water the shell swells, generally bursting lengthways, and releases the miracidium from its investing membrane, so that it can swim about with the aid of its cilia. In its structure it differs but little from the miracidium of Fasciola hepatica, as, for instance, in the lack of eyes; the two large gland cells situated on either side of the intestinal sac are also present in the miracidia of Fasciola hepatica.
Sarcode Globules.—This is a term applied to certain globules which at times appear in the miracidium and are later ejected. Some authors consider them as indicative that the miracidium has developed into a sporocyst, but Looss considers them to be degeneration products.
The Bilharzia mission, under R. T. Leiper, sent to Egypt by the War Office early in 1915, reports that cercariæ of bilharzia type were recognized in four of the commonest fresh-water molluscs around Cairo.
With material obtained from naturally infected Planorbis boissyi acute bilharziosis was experimentally produced in rats, mice, and monkeys. Infection takes place experimentally through the skin and also through the mucous membrane of the mouth and œsophagus. The miracidium, after entering the mollusc, develops into a sporocyst. This gives rise not to rediæ, but to secondary sporocysts, which, in turn, produce cercariæ. These, like the adult worm, differ from other distomes in lacking a muscular pharynx.
Schistosoma mansoni, Sambon, 1907.
According to Manson, Sambon and others, the eggs with lateral spines belong to a species different from Schistosoma hæmatobium. Infections with this species only are said to occur in the Congo, Southern States of North America, West Indies (Guadeloupe) and Brazil (Bahia). The following characters, according to Flu, differentiate this species: (1) In the male the transition from the anterior portion of the worm to the lateral fields (the infolded portions which form the gynæcophoric canal) is not a gradual one as in Schistosoma hæmatobium, but in this case the lateral fields rise suddenly, almost at right angles to the anterior portion. (2) The ovaries have a well-marked convoluted course as in no other schistosome. (3) The oötype is symmetrical in reference to the long axis of the body, its duct being lateral on the ventral side (Looss’ explanation of this we have already given). (4) The worms live exclusively in portal vein and tract. (As lateral-spined eggs occur also in the bladder, this is not exactly true.)
Schistosoma hæmatobium, Bilharz, 1852.
Male, four or five large testes. Gut forks unite late, so that the single gut stem is short. Female, ovary in posterior half of body. Uterus very long, voluminous, with many terminal-spined eggs, some lying in pairs. Vitellaria in posterior fourth of body. Cercariæ in Bullinus contortus and Bullinus dybowski (syn.: Physa alexandrina) in Egypt.
Schistosoma mansoni, Sambon, 1907.
Male, eight small testes. Gut forks unite early, so that the single gut stem is very long. Females, ovary in anterior half of body. Uterus very short; usually only one lateral-spined egg at a time in utero. Vitellaria occupy posterior two-thirds of body. Cercariæ in Planorbis boissyi in Egypt.