THE OPALINID CILIATE INFUSORIAXS. 345 



Representatives of this division are now found in Europe, Asia 

 and Malaysia, the Seychelles Islands off Madagascar, tropical Central 

 America, and southwestern, northern, and northwestern North Amer^ 

 ica. It is unfortunate that Indian Anura have been so little ex- 

 plored for Opalinids, for thorough knowledge of southern Asian 

 Opalinids might give light upon the presence of a member of this 

 group of Cepedeas in the Seychelles. Its presence in the Seychelles 

 and the absence of related Cepedeas in tropical Africa suggest that 

 it reached its present habitat by the Ceylon-Madagascar bridge at a 

 comparatively late period when the Seychelles-Madagascar- Africa 

 connection had been interrupted. But there is zoogeographic e\i- 

 dence from other sources that the Madagascar- Africa connection per- 

 sisted longer than the Madagascar-Ceylon connection (fig. 236). 

 We have here a bit of evidence that Madagascar separated from the 

 trans-Indian Ocean bridge before the Seychelles did so. The data, 

 however, are very scant and are not worthy of much emphasis. At 

 best, considering the nature and small amount of our material from 

 some regions, negative evidence, that is, absence of Opalinids of any 

 sorts from one of these areas, is of very little weight. But when 

 we have had a more comprehensive survey of these regional faunas 

 the negative data may be emphasized. 



The absence of Cepedeas of this group from Africa and their 

 presence in eastern Asia and America seems to indicate migration to 

 America from eastern Asia by way of Alaska. This is further borne 

 out by the presence of C. cantahrigensis in extreme northwestern 

 North America. Representatives of the group have passed south 

 into Texas, tropical Central America, and Brazil. Here again we 

 have evidence of extensive migration. From their present host dis- 

 tribution it seems these Cepedeas came to America in some Rana and 

 that some of them were adopted by an American Bufo and two 

 American Hylas. 



The table for division 6, above, shows one noteworthy fact, namely, 

 that almost identical Cepedeas {multiformis) occur in a Central 

 .Vmerican Hyla and a Japanese Rana. Forms like C. multiformis 

 and the similar C. cantahrigensis may well have been the original 

 immigrants from Asia. If so, the presence of these forms, so little 

 modified to-day, emphasizes a fact of great interest, of which there 

 is much evidence from many sources, namely, that the secluded and 

 uniform habitat in which many internal parasites live allows their 

 persistence for a long time without modification. This may be the 

 explanation of the eastern hemisphere and western hemisphere forms 

 being sometimes so similar that one feels compelled to place them 

 in the same species, though recognizing subspecific differences. An- 

 other similar instance is the close resemblance between the Austra- 

 83103—2.3 23 



