NO. 8 PARASITES METCALF I? 



The genus ZcUcridla arose in Patagonia, before the separation of 

 Patagonia from Antarctica. This separation occurred probably in the 

 middle Miocene. ZcUcridla did not arise until Patagonia had lost its 

 African connection, for the genus does not occur in Africa. In the 

 early or middle Tertiary it spread to Australia ; in the late Tertiary 

 to Tropical America. Its original hosts were southern frogs (lepto- 

 dactylids). Its presence in South America and Australia, and its 

 absence from Euro-Asia is, when carefully studied, as already noted, 

 evidence of former southern land connection between these continents. 

 To continue merely listing the things indicated by Metcalf's host- 

 parasite data from Anura and their opalinids would be wearisome, so 

 we will omit reference to the genera Ccpcdca and Opalina and their 

 subgenera, whose times and places of origin and times and routes of 

 dispersal were discussed, and will note further only some of the types 

 of conclusions suggested. 



Evidence was found as to the places and times of origin of the 

 several families of frogs and toads, and the routes by which, and 

 the times at which, they spread to the lands they now occupy. There 

 are similar indications as to a number of genera of the hosts, Bufo, 

 Polypcdatcs and Rana, for example. 



Spread of true frogs {Raninac) from the north into South America 

 has not occurred, except for one species, and there are no indications 

 of any southward wandering of Anura across the Isthmus of Panama 

 since its formation in the Middle Pliocene. On the other hand, there 

 has been extensive spread of Anura northward across this Isthmus. 



The Sonoran desert of northern Mexico and the southwestern 

 United States has been a hindrance to northward wandering of 

 southern frogs since the middle Pliocene, but has not held back the 

 tree frogs (Hylidae). 



Negative as well as positive evidence is often given. For example, 

 the absence of Zelleriella — the characteristic opalinid of the southern 

 frogs— from Euro-Asia indicates that southern frogs were never 

 in Euro-Asia. The alisence of the genus Opalina from South America, 

 though it is present in the toads (Bufo) in Central America, shows 

 that toads have not passed south across the Isthmus of Panama since 

 Opalina, a Tertiary immigrant from Asia, reached Central America. 

 Again the only Euro- Asian species of tree frog (Hyla arborea) with 

 its several subspecies is not endemic in Euro-Asia, but is an immigrant 

 from North America, for it carries a North American Opalina. 



This recital of a few of the indications from Metcalf's studies is 

 sufficient to emphasize the point here in view, namely, that host- 



