LIFE HISTORY OF THE LIVER-FLUKE. 99 



The Life History of the Liver-Fluke (Pasciola 

 hepatica). 



By 



A. P. Thomas, M.A., F.Ii.S., 



Ballinl College, Professor of Natural Science ia University College, Auckland, 

 New Zealand, late Demonstrator in the Anatomical Department, Uni- 

 versity Museum, Oxford. 



With Plates II and III. 



It has been known from very early times that the liver-rot 

 of various herbivorous mammals is a parasitic disease due to 

 the presence of very numerous flukes in the liver of the affected 

 animals. Amongst our domesticated animals the sheep is by 

 far the most frequent victim. The fluke disease is always 

 common in certain districts in England and in many parts of 

 the world; but in consequence of a succession of wet seasons 

 there was a serious outbreak of it in the winter 1879-80, and 

 it is estimated that in the United Kingdom 3,000,000 sheep 

 were then destroyed by it. Hence special attention was called 

 to the subject, and the research summarised in the following 

 paper was undertaken on behalf of the Royal Agricultural 

 Society of England. 



For the sake of convenience the subject is divided into the 

 following sections: — 1. Historical. II. Methods of In- 

 vestigation. III. Life-history. 



I. Historical. 



From what was known of the course of development amongst 

 the digenetic Trematodes, the nearest allies of Fasciola he- 



