FA SC TOLA HEPATIC A 



567 



shell gland. The egg now passes forwards into the uterus, and is evidently- 

 deposited in the bile-passages and escapes in the faeces. It is oval, yellowish- 

 brown, with a cap-like lid 0-13 to 0-145 millimetre in length by 0*07 to o'og 

 millimetre in breadth, and is seen to enclose a mass of yolk cells with one 

 ovum, which now segments and grows, using up the yolk cells, forming a 

 young form, called a ' miracidium,' 0-13 by 0-027 millimetre, which in a 

 few weeks escapes by the opercular opening if the egg is in water, and, being 

 ciliated, swims about as a conical larva, with a little anterior papilla and 

 two eye-spots. It has a cuticular epithelium, under which are muscular 

 layers, and contains a simple sac, like an alimentary canal, a cerebral gan- 

 glion, and an excretory system. There is a segmentation cavity (forming a 

 body cavity) between the alimentary canal and the body- wall. 



It now bores its way into the pulmonary cavity of some snail by means 

 of its anterior papilla; otherwise it dies in about eight hours. The varieties 

 of snail hosts are: Limncea truncatula Miiller, in Europe, Asia, Africa; L. 

 oahuensis in the Sandwich Islands; L. viator Orb in South America; L. humilis 

 Say in North America, in which it loses all its organs, and increases in size 

 rapidly, while cells grow from the wall into the primary body cavity, so that a 

 cyst is formed, called the ' sporocyst.' This has an external cuticle, a thin 

 muscular layer, and an epithelial lined cavity, containing collections of cells, 

 which develop into cylindrical forms, possessing a simple, short, tube-like 

 alimentary canal, with a pharynx, glands, and intestine, and a genital pore 

 near the anterior end. These forms, which are called RedicB, after the cele- 

 brated biologist Redi, force their way out of the sporocyst by making a wound, 

 which heals readily, and then wander about the snail, being especially abundant 

 in the liver. When fully formed they have a ridge running round the anterior 

 end, and a pair of blunt processes for locomotion posteriorly. 



Fig. 219. — LimncBa truncatula Muller. 



Inside the RedicB cells bud off from the body-wall and form the CercavicB. 

 which are not unlike a young Fasciola with a tail. 



The CercaricB possess cutaneous glands for the purpose of secreting the 

 cyst- wall of the next stage. They escape from the Redics by means of the 

 genital pore, and, leaving the snail, swim about in the water for some time, 

 finally becoming encysted on grass or water-weeds, and are then eaten by 

 sheep, inside which they escape from the cyst, and, working their way along 

 the bile-ducts, develop in six weeks into sexually mature flukes. 



Habitat. — The liver-fluke usually lives in the sheep, in which it causes the 

 disease called ' sheep-rot '; but infection can spread to man. 



Pathogenicity, — It causes the disease ' Halzoun ' in North Lebanon by 

 entering the pharynx. It is probably Hexathyridium venarum Treutler, found 

 in the anterior tibial vein, and the worms found in the portal vein by Duval 

 at Rennes in 1842; by Vital from Constanzia in 1874, by Giesler, in 1850, 

 in a foot; by Harris, in Liverpool, in an abscess. It may be Disto.num oculi 

 humani Ammon, 1833; Monostomum lentis Von Nordmann, 1832; and the 

 Distomum ophthalmicum Diesing, 1830. 



Fasciola gigantica Cobbold, 1856. 

 Synonyms. — Fasciola angusta Railliet, 1895; F. gigantea Cobbold, 

 1858. 



Definition.— Fasciola with short cephalic cone, almost parallel 



