CH. IX] OF DOMESTIC ANIMALS 307 



It is clear that the chances of any one larva meeting 

 with a L. truncatula and even then of boring a way into 

 a suitable tissue are very few. The infant mortality among 

 flukes must be enormous. In the life-history of those few 

 which are favoured by fortune there now occurs a series of 

 events which to a large extent compensate for previous 

 losses, and increase the prospects for the future, where, as 

 will be seen, the odds are all against the fluke. Occasion- 

 ally a sporocyst divides into two sporocysts. In any case 

 each sporocyst produces within it, from what may be 

 regarded as larval eggs, a number of secondary larvae 

 termed redice. A redia exhibits a decided step forward 

 towards the adult condition ; it possesses a mouth and 

 pharynx, and a short, but unbranched, digestive sac. The 

 redise are produced in succession and may be seen in all 

 stages of development within the cavity of the sporocyst. 

 When about O25 mm. long they become active and break 

 out from the sporocyst into the tissue of the snail. By 

 means of muscular contractions, aided by two blunt " feet " 

 near the hinder end,, they force their way into, generally, 

 the liver, eating the tissues as they proceed and, if numer- 

 ous, destroying the snail. Lutz mentions that in the 

 Hawaiian epidemic there was a great mortality among 

 L. cahuensis and that as many as two hundred redias were 

 found in a single individual. The redias may attain a 

 length of over 1 mm. A further multiplication of indi- 

 viduals derived from one successful larva now ensues. Each 

 redia produces, after the same fashion as the sporocyst 

 before it, a number of daughter redise which escape from 

 their parent by a special aperture placed laterally just 



202 



