OPALINID CILIATE INFUSORIANS — METCALF 609 



Opalinidae. Comparative anatomy, comparative development, and 

 geographic distribution combine to prove the phylogeny beyond 

 reasonable doubt. But while this cannot be gainsaid, some of the 

 hypotheses as to places of origin, times of origin, and routes and times 

 of distribution of the parasites and of their hosts stand on a different 

 basis. Some of the conclusions as to the latter are assured, but others 

 are not. If we grant that the prevalent hypotheses of paleocartog- 

 raphers are correct, the suggestions as to the origins of anurajis and 

 opalinids seem to combine the available data in the most acceptable 

 way. But paleogeography remains subject to revision. Reahzing 

 this, I have been surprised to find that the data as to anurans and 

 opalinids fit so well the conclusions of Arldt and Schuchert and other 

 paleogeographers. The only disagreement is that the data here 

 studied seem to demand a connection at some time during the Jurassic 

 or early Cretaceous period between Asia-Malaysia and Lemuria. It 

 is the ability of paleogeographic data and conclusions from them to 

 fit such data as the Anura and their parasites present that is one of the 

 chief evidences of the probable accuracy of the paleogeographic 

 conclusions. 



But my chief interest in these studies is not in the conclusions estab- 

 lished, but rather in the method of gathering and usmg concomitantly 

 data from organisms and their parasites. Tliis method should be used 

 for very many groups of animals and plants and their parasites, and 

 should always be in the thought of anyone monographing any group, 

 to see if significant data are forthcoming. It will prove a major tool in 

 reconstructing the ancient world and its faunas and floras. It is 

 unfortunate that the paleontological data for the Anura are so scant. 

 Except for this regrettable lack of fossils, the Anura and their Opalmi- 

 dae give an almost ideal complex of significant phenomena. Some of 

 the many groups having a distribution that is of especial interest as 

 to the question of routes for eastward and westward dispersal in the 

 Southern Hemisphere are the coeciliid, the characinid, and the cicb.lid 

 fishes and the lungfishes, the ostrichlike birds, and the craneflies. 

 Studies of the parasites of any of these southern groups might well give 

 chnching evidence like that from Zelleriella and the South American 

 and Australasian families LeptodactyHdae and Hylidae (see Metcalf, 

 1923a and b; 1928c). 



One further consideration should be noted— that the Pleistocene 



glacial period came too late to be of much significance in connection 



with the evolution and distribution of the Anura and their Opalmidae, 



most of this evolution having occurred long before Pleistocene times. 



SPECIATION IN OPALINIDAE 



The problem of speciation is fundamentally the same as that of 

 evolution. The processes of speciation are different for various groups 

 of organisms. Some species have been formed by sudden and extensive 



166877 — iO 10 



