463] LARVAL TREMATODES—CORT 17 



probably been described as Cercaria ephemera as it seems improbable 

 that Ssinitzin and Lebour have described the same form. The only 

 difference that can be definitely determined by comparing the descrip- 

 tions of Cercaria ephemera with Cercaria urbanensis is in the structure 

 of the posterior locomotor appendages of the cercaria. In von Linstow's 

 (1896:376-377) description of Cercaria monostomi both rediae and cer- 

 cariae are larger than in any of the other species, the arrangement 

 of pigment is different from that in Cercaria urbanensis, and no poste- 

 rior locomotor appendages are described. These may have been over- 

 looked as they are very small and not easily seen unless the animal is 

 studied alive. Cercaria lophocera described by Filippi (1857:5) from 

 Italy is entirely different from all other monostomes known. 



Two descriptions of monostome cercariae have been made from 

 North America. Leidy (1877:200-201) describes as M onostoma lucanica, 

 a form from Planorbis parvus. Unfortunately not enough detail is given 

 to make the comparison possible. The other form is described by Halde- 

 man as Cercaria hyalocauda. It has been impossible to find Haldeman's 

 original description. Evarts (1880) describes this species from Physa- 

 heterostropha. Altho so little detail is given that a minute comparison 

 cannot be made between this species and Cercaria urbanensis, certain 

 points can be definitely made out. Cercaria hyalocauda is about half 

 again as large as Cercaria urbanensis, and its cyst is much larger than 

 that of the latter species, being 0.32 mm. to 0.20 mm. It seems evi- 

 dent that the two forms are not identical. 



Altho monostome cercariae have been known since 1817, the life- 

 history of no one of them has been proven experimentally. Looss (1896 :- 

 192-193) argues from distribution and structural correspondence that 

 Cercaria imbricaia from Egypt is the larval form of Notocotyle triseri- 

 ale from the duck. Liihe (1909:178) suggests that Cercaria ephemera 

 is the larval form of either Notocotyle triseriale or Catatropis verrucosa 

 (Frol.), but cannot belong to Typhlocoelum flavum (Mehl.) on account 

 of differences in the digestive systems of the two forms. So little is 

 known of the monostomes of the United States that it is useless to gen- 

 eralize in regard to the life-history of Cercaria urbanensis. 



AMPHISTOME CERCARIAE 



Amphistome cercariae of two species were collected from speci- 

 mens of Planorbis trivolvis from three localities. Two snails out of 

 eighteen from Lawrence, Kansas had the livers infected with rediae 

 and very large pigmented cercariae. Out of large numbers of Planorbis 

 trivolvis examined from around Urbana, Illinois, one from a small pond 



