ANIMAL PARASITES 



169 



should require two such widely removed animals 

 as man and i^nat or mos(|uito to com|)]ete its 

 life-course, indeed, causes one to wonder what 



^"|L,^ I lo. A shet'p liuk, magnihed five ili.Linuter^ 



Other hidden marvels of natural life surround us 

 unseen. 



Of course this complicated change of hosts 

 makes the probabilities oi mature development 

 with this class ot organisms exceedingly small : 

 which IS a providential arrangement, for if the 

 tiex'elopment of these pests were less complicated, 

 animaldife might be in seri(.)Lis danger of exter- 

 mination. 



Besicles the liver-tluke, the sheep has a number 



