378 BULLETIN 120, UIsHTED STATES NATIONAL MUSEUM. 



Asia and North America and on through Central America to eastern- 

 most Brazil, and it spread from southeastern Asia by a route north 

 of the Himalayas to westernmost Europe and from Asia Minor 

 south to southernmost Africa. 



This all looks as if migration time of the Anura must be reckoned 

 in geologic periods rather than in years, but even a single, short, 

 geologic period, like the Pliocene, is long enough for wide wander- 

 ing, at least of some families. It is very evident that different fami- 

 lies and different genera are very different in the extent to which they 

 spread and in the rapidity with which they spread. 



Scharff (1911) writes (p. 552) : "It is quite evident that the genus 

 Taplrus could not have come across any Bering Strait land con- 

 nection in Pleistocene times and have traveled to Argentina before 

 tlic end of the Pleistocene period." This does not seem to me quite 

 so evident. The broad Opalinae evolved during the late Tertiary 

 in southern Asia. After this, Anura, probably Rana, bearing broad 

 Opalinae traveled during the late Tertiary from southern Asia by 

 way of Siberia and Alaska to America, gave their broad OfcHinae 

 to some Hylid, which changed the broad Opalinae to narrow 

 Opalinae. After this evolution of the narrow Opalinae in America, 

 a Hyla carried them back across the Alaska-Siberia connection and 

 on acroSiS all Asia to westernmost Europe and northern Africa (see 

 p. 355). Probably the westward passage of the Hyla from Alaska to 

 Siberia occurred before the Glacial period. If so, the Miocene and 

 the Pliocene periods together sufficed for the evolution of one 

 subgenus of Opalina^ its migration in its hosts to America, the evolu- 

 tion in America of the second subgenus of Opalina., and its subsequent 

 migration in its host back across the whole width of Euro-Asia and 

 even on into Africa. This is about as rapid spreading as for Tapirus 

 to pass during the Pleistocene from eastern Asia by way of Alaska to 

 Argentina. 



Our study of the structure of the Opalinidae and our discussion 

 of the distribution of the four genera and of their species, has led to 

 the conclusion that Protoopalina and Cepedea are old genera and that 

 Zelleriella and Opalina were more recently evolved. We have noted 

 also that the two older genera show fairly well demarcated subgeneric 

 groups of species, while the two younger genera do not do so, except 

 that in the genus Opalina we can distinguish the eastern forms, Opa- 

 linae latae^ from the Western Hemisphere forms, Opalinae augustae. 

 Is it the youth of the younger genera that accounts for their less di- 

 versified speciation? It may be. But a broad review of the Avhole 

 animal kingdom from this point of view would, I think, show that, in 

 many cases, groups destined to become highly diversified may acquire 

 a high degree of diversification soon after their first appearance. 



