503] LARVAL TREMATODES—CORT 57 



3. Acetabulum back of the middle of the body and smaller than 

 the oral sucker. 



4. Stylet about 0.030 mm. in length, six times as long as broad, 

 and with a thickening one-third of the distance from the point to the 

 base. 



5. Stylet glands, six or more on each side between the acetabulum 

 and the pharynx. 



6. Excretory bladder bicornuate. 



7. Very short prepharynx and small pharynx present. Esophagus 

 when developed short to of medium length. Intestinal ceca (when pres- 

 ent reaching to posterior end of body). 



Two European fresh-water cercariae, Cercaria limnaeae ovatae 

 von Linstow and Cercaria secunda Ssinitzin, without doubt belong to 

 this group. They both agree in all known particulars with the char- 

 acterization given above. No mention is made, however, in von Lin- 

 stow 's (1884) account of stylet glands. 



There are definite specific differences between the four forms which 

 constitute the Polyadenous cercariae. Of the two American forms 

 Cercaria polyadena has a larger body and tail, a smaller oral sucker, and 

 a larger number of stylet glands. Cercaria limnaeae ovatae is the largest 

 of the group, has much larger suckers than any of the others, and is 

 developed in larger sporocysts. The closest correspondence is between 

 Cercaria polyadena and Cercaria secunda Ssinitzin. These two species 

 are certainly very closely related. Cercaria secunda is, however, larger 

 in size and has slightly larger suckers and fewer stylet glands than 

 Cercaria polyadena. 



Some suggestion can be made in regard to the type of adults into 

 which the cercaria of this group develop. Cercaria limnaeae ovatae 

 has been assigned to Opisthioglyphe rastellus (Liihe, 1909:108) and 

 Ssinitzin (1905) suggests that Cercaria secunda may be the larva of a 

 Plagiorchis species. It would seem probable from the above facts and 

 the structure of the excretory and digestive systems that the Polyadenous 

 cercariae belong in Liihe 's subfamily Plagiorchiinae which contains 

 Opisthioglyple as well as Plagiorchis. The further development of the 

 two American forms is entirely unkown. 



CERCARIAE ORNATAE 



In 5 per cent, of the specimens of Physa gyrina from Rockford, 

 Illinois, the body contained a tangled mass of elongated, orange pig- 

 mented sporocysts. The tubes did not branch, they were of varying 



