70 PLATYHELMINTHES TREMATODA CHAP. 



the other hand, a far more extensive thickening of the wall of 

 the bladder sometimes occurs ; hard masses of eggs, uric acid 

 crystals, and other deposits, may lead to the formation of stones, 

 degeneration of the substance of the ureter, and eventually to 

 that of the kidney itself. The stone, indeed, has long been 

 known to be a prevalent disease in Egypt, and it is now known 

 to arise from concretions formed round masses of Bilharzia 

 eggs. From the portal vein, again, other Bilharzia, may gain 

 access to the rectum, or the liver, and it has also been found in 

 the lungs, and may give rise to most serious complications, if 

 indeed the patient lives. 



How infection occurs is a question to which at present no 

 satisfactory answer can be made. The attempt to introduce 

 embryos of Bilharzia into the common fresh-water animals of 

 Alexandria has hitherto proved fruitless (Looss a ), although there 

 seems little doubt that the comparative immunity of Europeans 

 from the disease is in some way owing to their drinking purer 

 water than the natives. Possibly, as Leuckart suggests, the 

 embryo becomes a sporocyst in man himself, somewhat as Taenia 

 murina is known to develop in the rat without an intermediate 

 host. 2 The immense numbers of the parasite in one host would 

 then readily receive an explanation. 



A Bilharzia, possibly B. haematobia, was found by Cobbold in 

 the portal vein of Cercopithecus fuliginosus ; and B. crassa infests 

 the cattle of Egypt, Sicily, and certain parts of India, but does 

 not produce haematuria. 



Of the other Trematodes of man and domestic animals there 

 is not room to speak fully. Distomum pulmonale, which occurs 

 in the lungs of the cat, tiger, and dog, as well as in man, is 

 especially common in Japan, China, Corea, and Formosa. D. 

 sinense and D. rathouisi have been also found in inhabitants of 

 these countries. 



Bisexual Trematodes. Zoologically, Bilharzia is interesting 

 from its bisexual condition. It is not, however, the only bisexual 

 Trematode. In cysts in the branchial chamber of Kay's bream, 

 Brama raii, two worms are found, which are probably the slender 

 male and the swollen female of the same species {Distomum 

 okenii}. The only doubt that can arise proceeds from the 

 tendency in all Trematodes for the male -organs to ripen before 

 1 In Leuckart, Die Parasiten d. Menschen, pp. 521-528, 1894. 2 Cf. p. 89. 



