42 THE BIOLOGY OF THE FROG CHAP. 



been recently found in some American species by Nickerson. 

 The peculiar genus Polystomum, characterized by having a 

 circle of several distinct suckers at the posterior end of the 

 body, is often found in the urinary bladder of frogs. Mono- 

 stomum ornatum Leidy occurs in the body cavity, and 

 Holostomum nitidum Leidy and Diplodiscus subclavatus 

 Dies, in the intestine of Rana pipiens. Monostomum 

 ellipticum infests the lungs of Ran a esculenta, and Tylodel- 

 phis rhachidis has been found in the neural canal of the 

 same species. Codonocephalus mutabilis Dies., Tetracotyle 

 crystallina Rud., and several species of Distominn occur in 

 an encysted state in various parts of the body of several 

 European frogs. 



Of Protozoan parasites there are several noteworthy forms 

 among the Infusoria. The large multinucleate Opalina com- 

 monly occurs in the intestine, especially the rectum. O. 

 ranarum, dimidiata, and intestinalis are found in Rana, 

 while other species infest other genera of Amphibia. Three 

 species of Balantidium, viz. entozoon Ehr, elongatum Stein, 

 and duodeni Stein, inhabit the alimentary canal of Rana, the 

 first species living chiefly in the rectum. Nyctotherus cordi- 

 formis Stein and Bursaria intestinalis Ehr. are intestinal 

 parasites ; the latter was found by Leidy in the intestine of 

 Rana pipiens. 



Of the flagellate protozoa there are two species of Bodo 

 which infest the intestine. Trypanosoma sangiiinis Gruby 

 occurs in the blood of several European species, and I have 

 found a closely allied if not identical species in the blood of 

 Rana pipiens. 



The largest number of protozoan parasites of the frog fall 

 within the exclusively parasitic class of Sporozoa. The Sporo- 

 zoa infesting the American species of Amphibia have received 

 little attention, but it is probable that a large proportion of 



