1920] Johnson: Life Cycle of Echinostoma Revolutum (Froelich) 365 



In order to discover how long cysts could live outside the body of 

 snails or in the tissues of dead snails, many infected specimens were 

 picked up at death, placed in small glass containers and examined 

 from time to time. In the handling of the dead snails, the body wall 

 was often ruptured and in this manner freed cysts were obtained. The 

 water in these small glass containers was not changed but more water 

 was added as evaporation took place. If the water had been changed 

 occasionally, I feel sure that the cysts would have lived longer than 

 they did because the bacteria and protozoa infection would not have 

 been so heavy. At the end of ten days every cyst appeared to be in a 

 healthy condition. The containers by this time had a very offensive 

 odor. At the end of thirty-six days about 75 per cent of the cysts 

 were alive, although in some cases part of these showed signs of 

 deterioration. At the end of forty-two days only 11 per cent of the 

 cysts were alive. Two days later only 5 per cent were alive. Thus 

 cysts in this unnatural condition sometimes live longer than six weeks 

 in dead snails or in the water. However, for the majority their life 

 was about five weeks. That this would be twice as long in the open 

 pond or stream, I do not doubt in the least. These results substantiate 

 the previous belief that cysts are quite hardy and long lived. Since 

 this echinostome cannot encyst in water, it means that any cysts that 

 reach the bottom of the pond must survive the decay of the snail. 



ADULTS 



Since the adult, Echinostoma revolutum, has been well described 

 by Looss (1899), Liihe (1909), Dietz (1910), and others, very little 

 description of this stage will be given. 



The adults of Echinostoma revolution, as previously stated, were 

 obtained in two ways, first, by examining different species of water 

 birds commonly found on the lake from which the snail, Physa occi- 

 d '< n I ulis, was taken. One species of duck, Marila marila, was found 

 to contain three adult echinostomes in its intestines. These adults 

 survived about fifty-five hours in the intestine of the duck, and twenty- 

 four hours in normal salt solution. During the last twenty-four hours 

 about forty-five eggs were produced, which were incubated and traced 

 to the full-grown miracidia stage. The second method of obtaining 

 adults was by feeding the encysted agamodistomes (cysts) found in 

 Physa occidentals to mongrel ducklings which were carefully pro- 

 tected from other trematode infections. In this way. eight full grown 



