EOT IN SHEEP. 361 



Eot developes most readily from the month of June to the 

 month of October. 



The fluke, distoma hepaticum, is found in the livers of 

 sheep in a perfect condition, with organs of generation deve- 

 loping or developed, and masses of ova surround the para- 

 sites. They are often packed together in scores in saccular 

 dilatations of the gall ducts, and I have seen the most extra- 

 ordinary specimens of livers, with varicose gall ducts en- 

 crusted with cholesterine and other solid principles of bile. 

 The ova, which abound in the gall ducts, pass out through 

 the intestine of the sheep, and fall into stagnant pools, 

 ditches, &c., or are washed from the land during rains into 

 streams. Most of the ova are fortunately destroyed as a rule, 

 but many are hatched, and embryos develope. Steenstrup's 

 investigations on this subject were very remarkable. The 

 embryos were found to acquire great activity, and would 

 move freely, owing to the vibratory cilia formed in their sur- 

 face. They are eaten by mollusks, the common physae or 

 limnese of pools and ponds. The embryos here acquire a 

 sort of hydatid form, are provided with alimentary canal and 

 organs of locomotion. By a process of interior budding 

 cercarice form, which are the young sucking worms, endowed 

 with great activity, and, thanks to a rudder tail, which ren- 

 ders them not unlike a tadpole, they can swim and find their 

 way into water; where they live free until some favourable 

 crustacean or mollusk appears, into which they pass by 

 means of spines developed on their head. They lose their 

 tail, and become encysted; their internal organs continue to 

 develope, and on the animal they are infesting being acciden- 

 tally swallowed by a sheep or other creature, they escape free 

 to pass into the liver, acquire generative organs, and lay eggs 

 for another generation. The metamorphoses here noticed are 

 probably similar for all trematode worms, and are presumed 



