1920] Johnson: Life Cycle of Echinostoma Revolution (Froelich) 337 



was changed daily. Shortly before the miracidia were due to emerge, 

 young snails were placed in the Syracuse dishes with the eggs. These 

 young snails were raised from eggs in aquaria which in no way could 

 have become infected. They were about six months old at this time. 



The fourth method was that of examining the various suspected 

 water birds from the lake from which all the snails were taken, and 

 particularly those birds which stay on the lake nearly or all the year 

 round. The following water birds were examined : one specimen of 

 Olor columbianus (Ord.) ; one of Anseranus semipalmata (Lath.) ; 

 three mud hens, Fulica americana (Gmel.) ; one shoveller duck, Spahda 

 clypeata (Linn.) ; one mallard. Anas platyrhynchos Linn; two ruddy 

 ducks, Erismatura jamaicensis (Gmel.) and two bluebills or more 

 accurately American scaup, Marila marila (Linn.). All but the Amer- 

 ican scaup gave negative results for echmostomes. From one of these 

 two ducks, adult echinostomes were obtained, which proved to be the 

 same species as those obtained from the experimentally fed ducklings. 



The tracing of the excretory system of the cercaria was accom- 

 plished by using the method described by Cort (1918). This method 

 of using living specimens for study by placing them under a No. 1 

 cover slip, although on the whole advantageous, has a decided dis- 

 advantage, since most of the water must be withdrawn to retard the 

 movement of the animal. When a slight amount more of water is 

 withdrawn, due to evaporation, the body wall quickly breaks in many 

 places. For this reason great numbers of cercariae had to be studied 

 before the system was completely worked out. 



ACKNOWLEDGMENTS 



I wish here to express my thanks to Mr. Bryant Walker of Detroit. 

 Michigan, and Mrs. Oldroyd of Stanford University for identification 

 of snail hosts ; to Mr. John Maclaren, Superintendent of Golden Gate 

 Park, for permission to obtain water-fowl in said park; to Mr. Char- 

 coutte of Golden Gate Park and those under his charge, and to Mr. C. 

 G. Budd, special game warden and policeman of San Francisco, for 

 collecting and shipping the swans, mud hens and ducks ; to Mr. F. H. 

 Ballon, of the Department of Zoology, for collecting snails and other 

 materials used in this study; to Dr. Joseph Grinnell and Mr. Tracy 

 I. Storer, of the Museum of Vertebrate Zoology, for identification of 

 vertebrate hosts; and to Mrs. Johnson for directing the experimental 

 feeding of chicks and ducklings and for help in various ways. 



