10 TROPICAL MEDICINE AND HYGIENE 



to adult is complex and that asexual multiplication takes 

 place outside the body from the sexually produced egg. 



From one egg, containing a single ovum, many flukes 

 are developed. The development of the fertilized ovum 

 commences in the uterine tubes, and in some the embryo 

 is formed before the eggs are passed by their host. In 

 other cases the ovum develops outside the body, so that 

 a mature embryo is formed inside the egg-capsule. The 

 eggs, when fully developed, undergo no further change 

 unless they are in water, when the embryo escapes 

 from the shell as a free-swimming ciliated body the 

 miracidium which in appearance may be mistaken for 

 an infusorian (fig. i, C). 



The larva, if free-swimming, wanders about till it finds 

 a suitable host, usually a mollusc, and then bores its way 

 through the body-wall. If not free-swimming, it is eaten 

 by the new host in its food. 



Having entered the tissues of the new or intermediate 

 host, the miracidium loses its cilia and becomes rounded 

 and motionless the Sporocyst (fig. i, E). This usually 

 occurs in the liver of the mollusc. In the interior of the 

 sporocyst young flukes Cercaricc may be formed. In 

 shape these resemble the adult form with the exception 

 that they are provided with a motile caudal appendage, 

 and in some instances with a boring spine at the anterior 

 extremity. This is a rare but comparatively simple 

 method. 



Often a still more complicated process takes place ; 

 the bodies, formed in the sporocyst do not in the least 

 resemble the adult form of flukes, and do not directly 

 develop into such adult forms. 



In this method of multiplication the contents of the 

 sporocyst are converted into tubular worm-like bodies 

 (fig. i, F, G), with a mouth and primitive intestine Redicr. 

 and it is in the body of such rediae that the cercariae, or 

 immature flukes, are formed. As several rediae are formed 

 and each of these forms several cercariae a double asexual 

 multiplication takes place (fig. i, H). These cercariae 



