THE OPALINID CILIATE INFUSORIANS. 355 



such as in America have come into extensive contact with the Hy- 

 lidae. The European Hyla which bears a narrow Opalina has not 

 succeeded in infecting any European Rana or Bufo. It was very 

 likely the change from the former host to a Hylid which stimulated 

 the adopted broad Opalina to diverge to the narrow form. The nar- 

 row Opalinae probably evolved quite late, for they have not yet 

 spread to South America, although any southward spread of the 

 Eanas. Bufos, or Hylids might well carry the narrow Opalinae also. 

 There has probably been land connection between North America and 

 South America by way of Central America since the latest Miocene 

 or more probably the Pliocene (fig. 237, p. 305). If the Opalinae 

 angustae first evolved in a Hylid from a broad Opalina adopted in 

 Central America or North America, this probably occurred quite late, 

 for two reasons : First, it must have been after the broad Opalinas 

 had evolved in Euro- Asia and had migrated to North America, and 

 the genus Opalina is apparently of later Tertiary origin, having 

 evolved from Cepedea after this genus had reached Asia proper from 

 India (figs. 236, 237; also see p. 346) ; second, it must have been after 

 the Hylidae reached Central America coming from tropical South 

 America, and the Brazilian home of the Hylids could hardly 

 have been united to the Ecuador-Central America-California-Alaska- 

 Siberia land strip until after it had become interrupted, probably in 

 the north, else the Hylids would have passed on in numbers into Asia. 

 This places the evolution of the Opalinae angustae from the Opalinae 

 latae in the Miocene or Pliocene. If it occurred in the Pliocene, the 

 Hylids may not have reached Central America until the Isthmus of 

 Panama was established. If the evolution of the narrow Opalinas 

 occurred as early as the Miocene, the Hylids must then have already 

 passed to Central America by way of the eastern Pacific land strip. 

 The later date is the more probable, the Isthmus being probably of 

 Pliocene origin. 



Summarizing the evidence as to the Opalinae, some of which will 

 soon be developed more fully in discussion connected with the several 

 families of Anura, we may say : First, as to the Opalinae latae, that 

 their absence from South America indicates that they were not in 

 South Atlantis in Jurassic times or early Cretaceous times (fig. 233) ; 

 that they apparently evolved from Cepedea in southeastern Asia or 

 the Malay Islands after Cepedea had reached continental Asia in the 

 late Tertiary (fig. 237), as discussed on page 346; that during this 

 period, or during the Pleistocene (fig. 238), they entered Japan, 

 Europe. Africa, and America by way of Siberia ; that they probably 

 entered America before the earliest glacial period, for a narrow 

 Opaline had time to evolve from them in America and spread back 

 across to Siberia and all Euro-Asia. Of the Opalinae angustae we 

 may say : That they evolved in North America, or possibly in Central 



