338 University of California Publications in Zoology [Vol. 19 



To Professor "W. W. Cort, under whose direction this study has 

 been made, I wish here to express my appreciation for his continued 

 interest and many helpful suggestions. 



EGGS AND DEVELOPMENT OF MIRACIDIA 



Prom adult specimens of Echinostoma revolutum found in the 

 intestine of the duck, Marila marila (Linn.), about forty-five mature 

 eggs were obtained, nearly all of which produced miracidia. Prom 

 adults of the same species raised experimentally in ducklings, several 

 hundred eggs were also obtained, some of which did not mature since 

 they were forced out by pressure from the uterus. The eggs from 

 both sources were alike in color, shape, and size variations, as would 

 be expected since the adults belonged to the same species. They meas- 

 ured in length from 0.094 to 0.119 mm., the majority being about 

 0.108 mm. These figures fall within the range of variation given by 

 Looss (1899, p. 679-684). His measurements show larger and smaller 

 eggs than mine, which is to be expected since he measured a larger 

 number of eggs from more adults. The color of the egg is usually 

 yellow or yellowish brown. 



In order to watch the eggs from day to day, they were placed in 

 Syracuse dishes containing tap water. To keep the eggs in a favorable 

 medium part of the water was changed daily. About fifteen eggs were 

 placed in each dish in a room where the temperature varied little from 

 70° P. 



At one end of the egg is usually to be found a slight thickening 

 of the shell which appears to be of a darker color. At the other end 

 is the operculum or cap. "When the eggs emerge from this echinostome 

 they are in the one cell stage (fig. 1). This condition can also be 

 readily determined by studying the eggs while still in the uterus. 

 Although little work has been done on echinostome eggs, it seems 

 probable that the one cell stage of development at the time of emerg- 

 ing is a family characteristic. Looss' drawing (1896, fig. 92) clearly 

 shows eggs of Echinostomum lUiputanum in the one cell stage near the 

 genital pore. Usually the two cell (fig. 2) and the four cell (fig. 3) 

 stages are formed within the first twenty-four hours. During this 

 time the yolk mass appears somewhat cellular. It is made up of two 

 materials, one of opaque granules, the other of an oily and semi- 

 transparent fluid. The granules are prominent and at this stage are 

 numerous and small. These two materials seem to be mixed with each 



