66 ILLINOIS BIOLOGICAL MONOGRAPHS [512 



Marie Lebour (1912) tried to substitute for Liihe's classification one 

 based on other characters. According to her classification the cercariae 

 are divided into two large groups depending on whether they develop 

 in rediae or sporocysts, and within these groups are formed small groups 

 of apparently related forms. As an attempt to form closely related 

 groups this work is very suggestive, but as a working classification 

 it has very limited value. In the first place there is little evidence 

 for the belief that development in sporocysts or rediae expresses funda- 

 mental relationship. Such widely divergent forms develop from spor- 

 ocysts as Bucephalus, tailless cercariae, stylet cercariae, etc. The most 

 important part of Miss Lebour 's work is her attempt to build up natural 

 groups of closely related forms centering around some well known 

 species, as for instance, her Spelotrema group centering around Spelo- 

 trema excellens. The following is the essential part of Lebour 's classi- 

 fication. 



Lebour 's Classification of the Cercariae 



A. Gasterostomata 



Cercariae develop in sporocysts. Mouth at middle of ventral sur- 

 face. Ex. Bucephalous polymorphus Baer. 



B. Prostomata 



Mouth at anterior end. 

 1. Distome cercariae 



Two suckers. 



a. Cercariae developed in sporocysts. 



(1) Gymnophallus group 



Cercaria tailless. Ex. Cercaria glandosa Lebour. 



(2) Fork-tailed cercariae 



Tail forked at its end. Ex. Cercaria douthitti 

 Cort. 



(3) Spelotrema group 



Free swimming stage with stylet. Encysted 

 cercaria tongue-shaped, covered with spines, with 

 long prepharynx and esophagus, short ceca not 

 reaching to the end of the body. Ex. Cercaria of 

 Spelotrema excellens. (?) 



(4) Stumpy-tailed cercariae 



Tail broad and stumpy. Ex. Cercaria brach- 

 yura Lespes. 



(5) Lepodora group 



Body covered with spines. Intestinal ceca 

 reaching nearly to posterior end of body.' Tail 



