THE OPALINID CILIATE INFUSORIANS. 377 



the Anura, but are abundant in the Bufonidae and the Leptodac- 

 tylidae and are well represented in the Gastrophrynidae. The Ce- 

 pedeas are not abundant in the lower families of the Anura, but are 

 very numerous in the Bufonidae and the Ranidae. The Opalinas 

 are very scantily represented in Discoglossidae (one doubtfully nor- 

 mal infection) and Pelobatidae, but are very abundant in Hylidae, 

 Bufonidae, and Ranidae. 



How rapid has been the spread of Anura and their Opalinids? 

 This is an interesting question upon which we have but limited data. 

 The Hylidae apparently reached northern South America from 

 Brazil in the early Tertiary. Before the glacial period they had 

 passed through Central America, the Antilles (the West Indies- 

 Central America connection was interrupted after the Pliocene), 

 and North America, and had crossed into Asia. The passage 

 through Alaska to Siberia probably occurred before the first Pleisto- 

 cene glaciation, and the passage from eastern Asia to western Europe 

 and northern Africa probably took place before this first glaciation 

 or after the last glacial extension, rather than during any of the 

 comparatively cold interglacial intervals. The migration from 

 South America to Central America, if by way of the Isthmus of 

 Panama, took place during the Pliocene, and the further extension 

 to western Europe miay well have been within this period. The 

 Leptodactylidae apparently passed through South America and Cen- 

 tral America and into the Antilles during the Pliocene, for prob- 

 ably before the close of the Pliocene the connection of the West 

 Indian lands with Yucatan and Honduras had been broken 

 (Vaughan, 1919). The Leptodactylidae may well have evolved 

 and have spread throughout Antarctica and its connected lands, 

 Patagonia, New Zealand, Australia, between the time just before 

 the separation of Australia from Papua and the time when Patagonia 

 separated from Australia. (Fig. 228.) 



The spread in South America of the Ranioiae^ a most vigorous sub- 

 family, seems not to have been at all rapid. (Fig. 230.) We 

 do not know how much longer they may have been in that continent, 

 but apparently they were there as early as the Jurassic. During the 

 time, however long or short it may be, they have not spread bej^ond 

 the uplands in the northwestern corner of the continent, except for 

 one species of Rana^ apparently a recent immigrant, which has passed 

 across the northern regions as far as the extreme eastern point of 

 Brazil. Apparently the northern genera Polypedates and especially 

 Rana are the vigorous members of the subfamily to-day. The 

 genus Rana Jias apparently spread since the middle Tertiary 

 from India east to Malaysia and Papuasia, north and east through 

 83103—23 25 



