Kansas Academy of Science. 255 



LIFE CYCLES OF CERTAIN TREMATODES. 



(Preliminary Paper) 



Eakl O'Roke. 



PRELIMINARY studies made during the past two years 

 show that fourteen species of larval trematodes, nine of 

 which are new to science, occur in Kansas fresh-water snails. 

 The accepted life cycle of the digenic trematodes is that the 

 adult occurs in a vertebrate host, where it deposits its eggs. 

 The eggs hatch out into ciliated free-swimming miracidia, 

 which enter snails, undergo parthenogenetic development, and 

 produce sporocysts, rediae, and finally cercariae, which are 

 tailed, free-swimming larvae. These cercariae encyst in the 

 water, and in that condition are taken into the digestive tract 

 of their definitive host. 



The widely varying conditions of infection in snails, the 

 differences in the behavior of various species of the cercariae, 

 their failure to encyst in some cases and their peculiar habits 

 of encysting in other cases, leads the writer to believe that the 

 life histories, when finally worked out, will show variations 

 from the accepted cycles. Perhaps some stages are omitted, 

 or modifications added. The work is being pursued at Kansas 

 University, where special aquaria have been fitted up for ex- 

 perimental determination of life histories. 



University of Kansas, Lawrence. 



