370 University of California Publications in Zoology [Vol. 19 



middle of May. By the process of metamorphosis and growth the 

 mother-rediae should have daughter-rediae inside ready to escape 

 through the birth pore by the middle of July. These daughter-rediae 

 in turn, I should expect to have grown to maturity and to have cer- 

 cariae escaping through the birth pore by the middle of August or 

 the first of September, a rapid development due to the warmer 

 weather. From the middle of August until November the cercariae 

 are known to develop rapidly and to be continually escaping from the 

 daughter-rediae to form cysts in other snails or planaria or to return 

 to the same snail. Since many cercariae do not leave the snail but 

 encyst just after emerging from the birth pore of the redia, some 

 encysted agamodistomes are certain to be formed. Also since from 

 September to November is the fall migration season, it is clear that 

 the cysts are formed just in time to be eaten with the snails by 

 migrating ducks and geese. 



As shown by experimental feeding of encysted agamodistomes to 

 young ducklings, the mature adult echinostomes appear in four weeks, 

 having at this time about five hundred eggs in the uterus. In the 

 winter home of the ducks and geese, numerous eggs undoubtedly are 

 being given off. This would make it possible for Echinostoma revo- 

 lutum to develop far south. 



The adult worms probably live for several years in the intestine 

 of the ducks and geese, producing eggs all the while. The length of 

 life of this adult echinostome could possibly be determined by feeding 

 the cysts to young ducklings and examining the feces from month to 

 month. 



Although the mother-rediae stage doubtless can be found during 

 any season of the year in California, the winter season is probably its 

 dormant period, as will be proved in case of the daughter-rediae. 

 Though probably found during any season of the year in California, 

 because some ducks and geese stay here all the year round, yet, as 

 before stated, I should expect to find this stage most abundant during 

 May, June and July. 



The daughter-redia stage, i.e., the rediae that produce cercariae, is 

 known to exist at all seasons of the year in California, yet it is found 

 most abundantly in the fall. That the germ balls grow little or not 

 at all during the months of December, January, February, and March 

 is evidenced by the fact that during the sixty-three days from Decem- 

 ber 6th to February 7th not a single cercariae was to be found, and 

 from February 7th to the first of April they were very rarely seen, 



