778 PAEASITIC DISEASES. 



9. Notwithstanding its abridged locomotive powers, tlie non- 



ciliated larva sooner or later gains access to the body of 

 an intermediary bearer, within whose tissues it becomes 

 transformed into a kind of sac or sjporocyst. In this con- 

 dition the larva is capable of developing other larvse in 

 its interior by a process of budding. The sporocysts vary 

 in character, and when highly organized are called redice ; 

 they are often also called nurses; the latter term being 

 generally applicable to all forms of trematode larvae 

 which reproduce by internal budding. 



10. The progeny of the more highly organized " nurses " 



(sporocysts or redise) are furnished with tails, in which 

 characteristic stage of growth they constitute the well- 

 known cercaricc or higher trematode larvse. In this stage 

 they migrate from their intermediary molluscan hosts, 

 and pass into the water to lead for a time an independent 

 existence. 



11. There is every reason to believe that before the cercaricc 



succeed in gaining access to their final or definitive 

 hosts, they re-enter the bodies of molluscs or aquatic 

 insects.^ This they accomplish by means of a boring 

 apparatus ; and, having previously cast off their tails, 

 they encyst themselves beneath the surface of the skin. 

 In this new situation they acquire a still higher degree 

 of organization, thus realising the so-called tailless or 

 pupa stage. 



12. The pupae or encysted cercarire are at length passively 



transferred, along with its fodder or its drink, into 

 the digestive organs of the ultimate host; and it is 

 thought that the cysts serve the purpose of a protective 

 covering until the larvae have passed into the true or 

 digestive stomach, in which organ the action of the 

 gastric juice, by dissolving the sac, liberates the pupce. 



* From the investigations of Mr. Thomas, it is assumed that the intermediate 

 host of the liver fluke is not the slug as supposed, but a small aquatic animal, which 

 has hitherto been overlooked, or that the roots of grasses play the part of hosts to 

 the larval forms of distomates. — ( Veterinarian, April 1882.) 



