THE OPALINID CILIATE INFUSORIANS. 371 



The genus Rana is found in Asia (both south and north of the 

 Himalayas), Japan, Formosa, the Philippines, Malaysia, Papuasia; 

 in Europe and northern Africa ; in tropical Africa ; in North Amer- 

 ica arid Central America, one species being known from the north- 

 ern third of the continent of South America; on the tip of the 

 northernmost peninsula of Australia, across from Papua, is a single 

 species of Rana^ perhaps a stray from Papua. The single South 

 American species seems to be a recent immigrant from the north by 

 way of the Isthmus of Panama, but its Opalinid parasites are not 

 known ; when known they may tell us its place of origin and the date 

 of its southward migration. Rana^ like its near relative Polype- 

 dates^ probably arose in India, or upon the India-Madagascar ridge, 

 at about the time the latter was breaking up, and, with Polypedates^ 

 entered continental Asia from India in the later Tertiary, spreading 

 to its other present habitats. Rana^ but not Polypedates^ passed 

 westward by a route north of the Himalayas to Europe, and passed 

 by way of the Nile valley into tropical Africa. Its spread from 

 India northward and westward to Europe and on to southernmost 

 Africa, and its spread northward and eastward to the whole of North 

 America and on into Central America, one species passing across 

 the Isthmus of Panama and as far as easternmost Brazil, rival the 

 spread of the genus Eyla from southeastern Brazil, first, westward to 

 Australasia and, second, northward through all America to Alaska, 

 passing on westward to Asia, Europe, and northern Africa. 



The presence of Rana in Papuasia, though absent from Australia 

 (except for one species at the northernmost tip of this continent, 

 very likely a stray), like the similar distribution of the Pelobatidae 

 and Gastrophrynidae already noted, is an indication that Papuasia 

 and Malaysia were at some time in union after Papua and Australia 

 had finally separated from one another. 



The presence in Wyoming of a fossil form assigned to the genus 

 Oxyglossus^ one of the Raninae, presents an interesting problem. 

 Oxyglossus is living to-day in India and Java. It apparently reached 

 Java from India in the late Tertiary (fig. 237) or later. Arldt's 

 charts show no connection between North America and Equatoria, or 

 the land masses into which Equatoria later became divided, at any 

 period between early Jurassic and the late Tertiary. According to 

 our paleontological records the Devonian was the period of the 

 rise of the primitive Amphibia, not, of course, including the Anura. 

 Schuchert (1915?), in mapping the early Permian continents, shows 

 broad connections between Europe and the African region of Equa- 

 toria, with wide connection between Europe and North America, and 

 we might possibly conceive the evolution of the Ranidae as having 

 occurred as early as the Permian. The existence of the genus 



