154 THE ANIMAL PARASITES OF MAN 



Oxen suffer less in general, but even in these animals " stray " 

 hepatic flukes are occasionally found in the lungs, enclosed in thick- 

 walled cysts. 



The HISTORY OF THE DEVELOPMENT of the liver fluke has been 

 discovered by R. Leuckart and P. Thomas. According to these 

 investigators the elongated miracidium (fig. 75), ciliated all over, 

 develops from the eggs of the liver fluke a few weeks after the" 

 latter (figs. 74, 86) have reached the water, and after it has become 

 free, the embryo penetrates a water-snail (Limnseus truncafulus, 

 Mull, L. minutus, Drap.) that is common in fresh water, and 

 can live in the smallest collection of water as well as in meadows 

 that have been flooded, and becomes a sporocyst (fig. 77). 

 The sporocyst first of all produces rediae, which remain in the 

 same host, and under certain circumstances it develops a second 

 generation of rediae and finally forms cercaria (fig. 80). The 

 latter become encysted on the meadows and are taken up by the 

 respective hosts with their food ; this takes place towards the end 

 of summer, while the sheep feeding on the pasture land in the 

 spring spread the eggs of the hepatic fluke, and sometimes the 

 entire animal, by passing them with their faeces. 



In districts where Limnceus minutus is absent, analogous 

 species act as the intermediary hosts, of which one example, 

 according to Lutz, is the Limncem oahuensis l in the Sandwich 

 Islands. 



[The host in Europe is Limnceus truncatulus. This snail 

 extends from Siberia to Algeria and Sicily, and according to 

 Captain Hutton is a native of Afghanistan. It also occurs in 

 Thibet, Amoor, Morocco, Tunisia, Canary Islands and the Faroe 

 Islands. It deposits its eggs or spawn upon the mud around 

 ponds, ditches, and streams. The eggs are laid in batches of 

 thirty to a hundred, each snail laying as many as 1,500 eggs ; 

 they are united into strips of a gelatinous substance. In about 

 two weeks young snails appear. It is amphibious, being more 



1 The most important literature is as follows : Stieda, L., " Beitr. z. Anat. d. Plattw. 

 I." (Arch. f. An. u. Phys., 1867, p. 52); " Ueb. d. angebl. inn. Zusammenh. d. mdnnL 

 u. weibl. Org. bei. Trent." (Ibid., 1871, p. 31); Sommer, L., "Anat. d. Lebereg." (Z. f. w. 

 Zool., 1880, xxxiv., p. 539); Mace, E., Rech. anat. sur la grande douve du foie. These 

 de Nancy, Paris, 1882 ; Leuckart, R., " Z. Entw. d. Lebereg." (Arch. f. Naturg., 1882, 

 i., p. 80); Thomas, P., "The Life Hist, of the Liver-Fluke" Quart. Journ. Micr. 

 Sc., 1883, xxiii., p. 99); Schaper, " Die Leberegelkrankh. d. Schafe" (Dtsch. Ztsch. 

 /. Thiermed., 1889, xvi.); Lutz, A., " Z. Lebensgesch. d. Disl. hep" (C. f. B. u. P., 

 xi. f p. 783 ; xiii., p. 320); Coe, W. R., " Bau des Embr. v. Dist. hep." (Zool. Jahrb. 

 Abth., ix., p. 561); Havet, J., " Contrib. al'etud. d. syst. nerv. d. trem." ("Cellule," 

 1900, xvii., p. 351). 



