i86 



PRACTICAL ZOOLOGY 



The Liver Fluke. — The liver fluke is a flatworm which lives 

 as an adult in the bile ducts of the liver of sheep, cows, pigs, etc., 



and is occasionally found in man. 

 Figure 107 shows the shape and 

 most of the anatomical features 

 of a mature worm. The mouth 

 (0) is situated at the anterior end 

 and lies in the middle of a mus- 

 cular disk, the anterior sucker. A 

 short distance back of the mouth 

 is the ventral sucker (S) ; it serves 

 as an organ of attachment. Be- 

 tween the mouth and the ventral 

 sucker is the genital opening 

 through which the eggs pass to 

 the exterior. The excretory pore 

 lies at the extreme posterior end 

 of the body. 



The alimentary canal resembles 

 that of Planaria, and the repro- 

 ductive organs, as the figure 

 shows, are very complex. One 

 liver fluke may produce as many 

 as five hundred thousand eggs, 

 and since the liver of a single 

 sheep may contain more than 

 two hundred adult flukes, there 

 may be one hundred million eggs 

 formed in one parasitized animal. 

 The eggs pass through the bile 

 ducts of the sheep into its intes- 

 tine, and finally are carried out of 

 the sheep's body with the feces. Those eggs that encounter 

 water and are kept at a temperature of about 75 F. continue 

 to develop, producing a ciliated larva (Fig. 108, a), which es- 



Fig. 107. 



Anatomy of the liver 



fluke. 



D, anterior part of intestine 

 (posterior part not shown) ; Do, 

 yolk-glands ; Dr, ovary ; O, mouth; 

 Ov, uterus; S, sucker; T, testes. 

 (After Sommer.) 



