432 
ZOOLOGY: M. M. METCALF 
Proc. N. a. S. 
UPON AN IMPORTANT METHOD OF STUDYING PROBLEMS 
OF RELATIONSHIP AND OF GEOGRAPHICAL DISTRUBU- 
TION 
By Maynard M. Mktcai^f 
The Orchard Laboratory, Oberun, Ohio 
Communicated by H. S. Jennings, May 28, 1920 
In the course of the study of one hundred and thirty-four species and 
twenty subspecies of Opahnidae I have found data of great significance 
as to the geographical distribution and the former migrations of the 
Anura, and I wish to call attention to the importance of the method of 
studying such problems, in the case of each group of animals and plants, 
from the point of view both of the members of that group and of their 
parasites. A couple of illustrations will suffice to show how such study 
of a double series of data may present indisputable evidence as to the 
interpretation of the phenomena of present distribution of a family of 
animals. 
The Leptodactylidae are the characteristic "frogs" of tropical and south- 
temperate America. They are found also in fair abundance in Australia 
and Tasmania and nowhere else. This has been taken to indicate former 
land connection between Patagonia and Australia by way of Antarctica. 
There are those, however, who have questioned this conclusion, believing 
the resemblance between these American and Australian "frogs" to be 
due to convergent or parallel evolution. But the latter hypothesis is 
definitely excluded by a study of the Opalinid parasites of the Lepto- 
dactylidae. 
There is a genus of flat binucleated Opalinidae abundant in South 
America and Central America and spreading into the Antilles and a little 
into the southern part of North America. This genus, which I am naming 
Zelleriella, is the characteristic Opalinid parasite of the Leptodactylidae. 
The point of interest in the present connection is the fact that both 
American and Australian Leptodactylids have Zelleriella parasites, and 
the Australian Zelleriellas so closely resemble the American forms that it is 
difficult to separate them specifically. It might be conceivable that the 
Australian and American "frogs" assigned to the family Leptodactylidae 
may not be closely related and that their resemblances are due to parallel 
or convergent evolution, but it is not possible that both the Leptodactylids 
and their Opalinid parasites have evolved in parallel or convergent lines on 
the American and Australian continents. Such a coincidence is altogether 
improbable. Zelleriella is confined to Southern America and Australia. 
Study of the Opalinid parasites of numerous families and subfamilies of 
Anura has given indication of a number of interesting things. It indi- 
