246 BULLETIN 120, UNITED STATES NATIONAL MUSEUM. 



It is of interest if the tadpoles of this frog are infected while the 

 adults are not known to carry Opalinids. Somewhat similar rela- 

 tions obtain in Tlyla versicolor, for, though only a small percentage of 

 the adults of this species harbor Opalina, the many tadpoles studied 

 have all been abundantly infected with O. hylaxena. Possibly the 

 tadpoles of Rana cateshetana and Rana gnjlio may carry Opalinids, 

 though I have examined many tadpoles of the former species with- 

 out ever finding these parasites. The adults of either species of bull- 

 frog have never been reported as infected, excepting specimens of 

 the former species introduced into Hawaii and from there imported 

 into California. Native American specimens of these species have 

 proven barren. 



There are intestinal protozoa, other than the Opalinidae, which, 

 while not reported from adult Anura, are well known from the 

 larvae, as for instance Giardia. Professor Kofoid, in conversation, 

 suggested that the change from the vegetarian diet of the tadpoles 

 to the carnivorous diet of the adults may account for the disappear- 

 ance of the Giardia at" the time of the metamorphosis of the host. 

 There are changes in the intestinal tract itself at this time, changes 

 involving reconstruction of the tissues of the host, and probably ac- 

 companied by a period of fasting. If this change of diet and the 

 accompanying tissue changes involving abstention from food in- 

 fluence unfavorably the Opalinids in some species of hosts, they are 

 but little, if at all, hurtful in other species, for Opalinids are abund- 

 ant in most adult Anura. It is perhaps worth noting that the green 

 frog and the two species of bullfrog mentioned are our largest Ameri- 

 can frogs and are the only North American frogs not known to 

 harbor Opalinids when adult. On the other hand adult Bufos of 

 several species of even larger size are abundantly infected with 

 Opalinids. 



The tadpoles of Rana catesheiana, R. grylio, and R. clamitans live 

 over one or even two winters in the tadpole state. It seems probable 

 that the tadpoles of a previous season may directly infect the tadpoles 

 of a new season, so that there is not need of their passing through the 

 difficult (?) metamorphosis perod of their host, Brumpt (1915) has 

 shown that among European Anura the Opalinids in the older tad- 

 poles regularly go through a period of rapid division followed by 

 encystment, just as they do in the adult Anura in the spring, and 

 that younger tadpoles become infected from these ejected cysts. Any 

 species of Anura whose tadpoles live over winter might then readily 

 show Opalinids in the tadpoles and not in the adults. 



THE GENERA AND THE SUBFAMILIES OF THE OPALINIDAE. 



After the foregoing description of the species in the family, the 

 characters of the several genera are clear. Protoopalina includes 



