88 LIFE-HISTORY OF PARASITES. 



This is especially true with regard to immature encysted forms, which 

 often live for several decades. With regard to Echinococci and muscle- 

 Trichince, it is well known that in some instances they have lived over 

 twenty years, whilst their corresponding sexual forms perish in a few 

 weeks. 



The changes undergone by those Entozoa that die in their host, 

 and remain there, differ according to circumstances. Some pass 

 through the process of mummification, others that of fatty degenera- 

 tion, and others again calcify. 



