6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8l 



Australasia. Origin in America seems indicated. If so, their spread 

 to Australia must have been before the toads (Bitfo) with their very 

 different opalinid parasites {Ccpcdca)^ had reached the South Ameri- 

 can home of southern frogs. There is much evidence of the presence 

 of an effective barrier, perhaps a shallow sea, across what is now the 

 region in South America south of the East Brazilian highlands, sepa- 

 rating them from Argentina, Chile and Patagonia. If the southern 

 frogs and ZellericUa arose in the southern part of South America 

 and if Biifo and its Cepedea parasites were of northern origin, as 

 seems on many indications to be true, the origin of the southern frogs 

 and ZcllerieUa and also the time of their spread to Australia must 

 have been before the obliteration of this South Brazilian barrier 

 (sea?) stretching from the Atlantic to the Pacific Ocean, or else 

 Bufo, carrying Cepedea would have spread with the southern frogs 

 to Australia. But this it did not do, for Bufo and Cepedea are un- 

 known from Australasia. Patagonia united with Brazil during the 

 middle Tertiary, perhaps about the middle of the Miocene period. The 

 southern frogs and ZcUcricUa apparently evolved before that time in 

 southern vSouth America or i\ntarctica and had reached Australia 

 before Australia separated from Antarctica. 



In a similar way the present occurrence of the Hylidae (tree- 

 frogs), interpreted in the light of their parasites, indicates a southern 

 origin and a southern dispersal. But we are interested, at this point 

 of our discussion, merely in illustrating the value and method of using 

 data from both hosts and parasites together and not in establishing 

 particular hypotheses, so we will not here enter on a discussion of 

 the further evidence from the Hylidae. 



Having in mind this illustration of the host-parasite method, let 

 us review briefly the use thus far made of the method and a few of the 

 conclusions and hypotheses as to which it has given evidence. Then 

 we will briefly consider possible extensions of the use of the method to 

 other groups of hosts and parasites. 



Only a few students have used host-parasite data for evidence as 

 to genetic relationships of hosts, their origin and their migration 

 routes, or as to paleogeographic prol)lems, or as to all three. 



^ Opalina does not occur in South America in toads or in any other hosts, 

 though a number of species of Bufo in Central and North America carry 

 Opalina. The toads of South America probably came from Asia in the Creta- 

 ceous, before the genus Opalina had evolved, and came by a route that did not 

 include the continent of North America as at present formed. Opalina probably 

 evolved in soutlieastern Asia in the earl}^ Tertiary (c/. Metcalf 1923). 



