1920] j Jx nson ; Life Cycle of Echinostoma Rcvolutum (Froclich) 343 



rediae in these snails, and although I have not traced the cycle of the 

 daughter-rediae, .yet I feel quite certain that there is only one such 

 generation. Because of the fact that I believe only one generation of 

 daughter-rediae to exist, I shall call the rediae enclosing daughter- 

 rediae the mother-rediae. These mother-rediae, I feel quite certain, 

 have been derived by metamorphosis from miracidia, as were the 

 mother-rediae found in the young experimental snails. 



This viewpoint is supported by the fact that of the thirteen snails 

 found to harbor the mother-rediae, eleven contained only a few rediae, 

 and of these there were never more than four or five mother-rediae, 

 usually less. In the two cases where mother-rediae were found in 

 snails having many rediae producing cercariae, these mother-rediae 

 were limited to three or four in number. Had there been more 

 than one generation of daughter-rediae, then numerous rediae with 

 daughter-rediae inside would have been found since the daughter- 

 rediae and germ balls inside of one redia often exceed seventy. 



Further only one generation of daughter-rediae is necessary to 

 produce the average number of rediae found in a single snail. The 

 cases of two or three hundred rediae being found in one snail could 

 be explained by two. three, or four miracidia finding their way into a 

 single snail, which undoubtedly happens many times. Figure 26 

 shows a mother-redia containing ten daughter-rediae in which the 

 pharynx and digestive sac is clearly distinguishable besides thirty-one 

 good sized germ balls and many smaller ones. In another mother- 

 redia were found seventy-one daughter-rediae and good sized germ 

 balls as well as many smaller ones. 



When the daughter-rediae emerge they measure from 0.180 to 

 0.250 mm. in length, depending on the degree of contraction, and con- 

 tain small germ balls (fig. 29). At the time of emerging the activity 

 is usually quite pronounced. The shape is nearly like that of a fully 

 developed redia with quite prominent posterior projections, but the 

 "collar" and birth pore are very small or entirely absent. 



The daughter-redia stage was not found before December, 1918, 

 but this is readily explained by the fact that only those snails having 

 a heavy infection were examined carefully, since the material was so 

 abundant. It is also likely that the daughter-redia stage is somewhat 

 seasonal and thus the chance of finding it is greatly reduced. 



The daughter-rediae find their way out through the birth pore one 

 at a time, thus allowing room for other germ balls to increase in size. 



