THE OPALINID CILIATE INFUSORIANS. 331 



port of the single infection of ZellerieJla in an Asiatic toad is so re- 

 markable and so indefinite that unless it be confirmed it can hardly 

 be accepted for discussion of distribution. 



It seems in agreement with the data at present Imown to suppose 

 that a great continental mass existed in the Southern Hemisphere up 

 into Miocene times (fig. 236), and that upon this continent, including 

 Australasia and southern South America, there were Leptodactylids 

 which had ZellerieUa parasitic in them. Bufo was not in this 

 Antarctic fauna. At this time there was across south-central South 

 America a shallow sea connecting the Atlantic and Pacific Oceans, 

 which, from the evidence of the Andean strata, seems to have per- 

 sisted to a time as late as the last of the Miocene or apparently the 

 early Pliocene. But earlier than this, during the Miocene, the region 

 to the south of Patagonia subsided and Patagonia became separated 

 fi'omGraham'sLandjthe land route from Patagonia to Australia being 

 thus closed. The separation of Patagonia from Australia occurred be- 

 fore Patagonia became definitively united to tropical America. After 

 the establishment of land connection between the northern and south- 

 ern portions of South America, the toads passed southward to occupy 

 Patagonia, the Leptodactylids at the same time passing northward 

 into northern South America, Central America, and the West Indies. 

 When the toads and the Leptodactylids met, the latter gave Zelleri- 

 eUa to the toads. We wilj discuss later the evidence as to the origin 

 and spreading of Bufo and the Bufonidae. 



ZellerieUa, now overwhelmingly tropical American, probably arose 

 in Patagonia- Argentina and we may suppose that it arose only a short 

 time before Australia separated from Patagonia, since we know as 

 yet but one species of ZellerieUa from Australia. Wlien Patagonia 

 united with tropical America, the Leptodactylidae and their Zelleri- 

 ellas passed throughout tropical America. There may have been 

 some Bufonidae with them, but, if so, of other genera than Bufo. 

 Bufos, and other genera of Bufonidae, were doubtless already pres- 

 ent in tropical America, for an Africa-America trans-Atlantic 

 bridge had probably brought Bufonidae from Africa long before the 

 Pliocene (p. 299) . ^Hien they met the Leptodactylids, the Bufonidae 

 adopted the Zelleriellas, but did not in Central America give their 

 own Cepedeas to the Leptodactylids. 



A land connection between the West Indies, the Bahamas, and 

 the continent apparently must have been in existence after the north- 

 ern and southern portions of South America were united, for, as the 

 Leptodactylids came north they were able to pass to the Antillean 

 region, carrying their Zelleriellas with them. The immigrant toads 

 now living in the West Indies bear adopted Zelleriellas, very likely 

 adopted before their immigration from the continent. The Dendro- 

 hathiae are also represented in the Antilles as well as upon the conti- 



