THE OPALINID CILIATE INFUSOEIANS. 379 



One therefore suspects that Zellerlella is to-day a very compact genus, 

 not merely because it is comparatively young, but because stability 

 is in " the nature of the beast." ^ 



We have studied the phenomena of geographical distribution of the 

 Anura, using two sets of data, the first set presented by the Anura 

 themselves and the second set given by their Opalinid parasites. It 

 is clear that the two lines of evidence together have many times the 

 value possessed by either set of data alone. For example, it might 

 perhaps be possible, though difficult, to regard the Leptodactylids of 

 Australia and South America as of distinct origin, their resemblance 

 being due to convergence or parallel evolution. Hans GadoAV (1909) 

 accepts this general viewpoint in such cases of puzzling geographic 

 distribution.^*^ But such a belief becomes impossible in any instance 

 in Avhich we find that the apparent!}^ related Anura have closely 

 similar or almost identical parasites. Parallel development, or con- 

 vergent evolution of both the hosts and their parasites is too large a 

 dose for even the most credulous to accept. It is just this sort of 

 crucial evidence which is presented in certain cases by a concomitant 

 study of the Anura and their Opalinidae. There is great opportunity 

 for the development of similar double or multiple lines of evidence 

 from very many groups of animals and their parasites. To be sure 

 the Anura are particularly favorable when we are considering ques- 

 tions of land connections, for they are terrestrial or fresh-water forms 

 and are unable to endure salt water. Bufo inarinus is said to be 

 found sometimes in brackish water and even to lay its eggs in such 

 water, but this statement lacks confirmation. Darwin (1875) notes 

 one Indian species which endures salt water, and in the Philippines 

 Pearse (1911) found a species of Ran-a (?) entering salt water in the 

 crab holes on the mud flats, and he also found in several pools tad- 

 poles in all stages up to metamorphosis in water containing up to 

 2.64 per cent of sodium chloride. In general, as Gadow says (1909, 

 p. 71) : " The Amphibia are bound absolutely to the land and to fresh 

 water ; transportation across salt w^ater is not excluded, but must be 

 accidental and is not a case of regular 'spreading'." (Also p. 72) : 

 " Common salt is poison to the Amphibia ; even a solution of 1 per 

 cent prevents the development of their larvae. Consequently seas, 

 salt lakes, and plains incrusted with saline deposits act as most effi- 

 cient boundaries to normal spreading. * * * Solutions of lime are 

 likewise detrimental to many species, and it is a general fact that 

 limestone terrain is poor in Amphibian life, unless, of course, suffi- 

 cient accumulation of humus counteracts or prevents the calcareous 

 impregnation of the springs and pools in meadows." We can there- 



»» " The occurrence of four species of Hylella in South America, one in Australia, and 

 one In New Guinea indicates that this is not a natural genus" (p. 75). 



