CH. IX] OF DOMESTIC ANIMALS 305 



Fig. 52. Diagram of digestive and excretory system of Distomum hepaticum 

 x about 8. From Leuckart. 



1. Mouth. 2. Pharynx. 3. Eeproductive pore. 4. Branch of 

 alimentary canal. 5. Branches of excretory system. 6. External 

 opening of excretory system. 7. Nerve-ring. 



in turn may give off numerous ramifications extending 

 through the body. There is no anus. The reproductive 

 organs consist of a simple ovary, a pair of testes and 

 numerous accessory glands : the entire genital system is, 

 relative to the size of the animals, enormous, and a very 

 large number of eggs is produced by each individual. 

 With very few exceptions Trematodes are hermaphrodite, 

 and some are undoubtedly capable of self-fertilisation. 



The most notorious of all the Trematodes is the Liver- 

 fluke, Distomum hepaticum 1 , the cause of the disease known 

 as " sheep-rot." The adult fluke is about an inch and a 

 half long and is found in the bile-ducts and liver of the 

 sheep and other domestic animals of similar habits. It 

 has been known to occur in man. The eggs are deposited 

 in the bile-ducts of the host and pass out with the faeces. 

 They are protected by thick chitinous shells, and are about 

 O13 mm. long and 0*08 mm. broad. Development of the 

 embryo has already begun within the shell before the egg 

 gets free from the body of the host, but it proceeds no 

 further unless there be certain conditions, namely, moisture 

 and a fairly high temperature, in the spot where the egg 

 chances to fall. The optimum temperature has been found 

 to be from 70 75 F. Given the proper conditions there 

 issues from the egg-shell, which opens by a circular lid at 



1 Thomas, Q.J.H.S. xxm. 1883, and Roy. Agric. Soc. Journ. (2) 1881, 

 1882, 1883. 



L. 20 



