336 University of California Publications in Zoology [Vol. 19 



the missing stages been traced. This lack of information is due prin- 

 cipally to the complex life cycle. The chief difficulties involved are 

 those of connecting exactly, by experimental feeding, the encysted 

 agamodistome with the adult echinostome and of finding the exact 

 species or genus of snail into which the miracidium will enter 



Knowledge concerning the entire excretory system of any stage of 

 the life cycle of an echinostome is even less complete than that of the 

 life history. This lack of knowledge is due largely to wrong methods 

 of study which formerly consisted of using only preserved specimens. 



At the suggestion of Professor W. W. Cort, the writer undertook 

 in August, 1917, to work out the excretory system of an echinostome 

 cercaria which later proved to belong to Echinostoma revolutum 

 (Proelich). After tracing the ramifications of the tubules of the 

 excretory system of the cercaria, work on this system in the redia was 

 taken up. This led to the search for other stages suspected to exist 

 in the life cycle of this species. The species chosen proved to be favor- 

 able for both types of work. 



METHODS OF STUDY 



The solution of the life cycle was undertaken in four ways. The 

 first method was that of examining carefully a large number of snails, 

 Physa occidental-is Tryon, from Stow Lake, Golden Gate Park, San 

 Francisco, in which the cercariae were present to see if there might 

 not be found other stages if studied during the entire year. Careful 

 examination of four hundred of these snails showed that 86.75 per 

 cent were infected with either the encysted agamodistomes or rediae or 

 both. In addition, one other stage, the daughter redia, previously 

 never reported for echinostomes, was found. 



The second method was experimental. It consisted of feeding large 

 numbers of encysted agamodistomes to white mice, New Zealand 

 rabbits, white leghorn chicks, and mongrel ducklings. They were all 

 protected in every way from other trematode infections, the last two 

 being hatched in incubators and raised in brooders. The ducklings 

 and chicks were never allowed near water or soil, there being always 

 a board floor in the brooder. Their food was also carefully selected. 

 Negative results were obtained from the experiments with the mice, 

 rabbits and chicks, but the ducklings gave positive results. 



The third method was also experimental. It consisted in hatching 

 the echinostome eggs in Syracuse dishes in which most of the water 



