1920] Johnson: Life Cycle of Echinostoma Ee volution (Froelich) 369 



Although all the stages in the life cycle have been found and the 

 necessary hosts are known, yet the time of the appearance of each 

 stage and its duration are not known. 



In regions where there is a definite winter or freezing period, I 

 believe, each stage will be found during a certain season of the year. 

 In the San Francisco Bay region of California, where light frosts 

 may sometimes occur, the seasonal distribution of each stage is hard to 

 solve. For this reason, California is not a good place to work on this 

 particular part of the problem of the life cycle, although very favor- 

 able in every other respect. I should expect to find, and do find here 

 considerable overlapping of the stages taking place. 



During the migration of water birds in the spring and fall of the 

 year, the great majority of the eggs are doubtless dropped in Cali- 

 fornia ponds and streams. Although a few ducks and geese nest in 

 the bay region of California, and thus some eggs are probably dropped 

 in the summer time also, the great majority of the ducks and geese 

 raise their young farther north. If the eggs are dropped into the 

 ponds and streams during the fall migration, they doubtless remain 

 practically dormant during the winter season. This conclusion is 

 reached because the temperature of the water, although seldom at the 

 freezing point, is sufficiently low to keep the germ balls in the redia 

 from developing. This is borne out by the work of Nakagawa (1917) 

 in connection with the development of the eggs of Paragonimus irester- 

 manni Kerbert. He makes this statement concerning the incubation 

 period of these eggs: "The rate of development of the miracidia varies 

 with the temperature and is retarded by cool weather. During the 

 summer in Shinchiku (Formosa), i.e.. from May to October, the melon 



s 1-like miracidia develop in 14 to 15 days, begin to move in 19 to 22 



days, and batch in 23 to 28 days. In March and April they take some 

 weeks to hatch, and the miracidia remain for a long time within the egg 

 even though they are as lively as in the warm season. From November 

 to February or March no development was noted, though the eggs were 

 watched constantly. According to my observations, the temperature 

 for hatching is 25-31° C, and embryonic development ceases below 

 25° C. Manson gives 26-34° C, Nakahama 30° C, and Garrison and 

 Leynes 25-34° C. At 37° C. the eggs seem to disintegrate." If the 

 eggs are vented during the spring migration, doubtless they begin 

 development immediately. Thus the eggs produced during the fall and 

 spring seasons of the year would develop into miracidia at about the 

 same time. These miracidia probably appear about the first to the 



