22 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8l 



terial. But best of all ciliates for such studies seem to be the archaic 

 group, the prociliates.' including only the Opalinidae, the basis of 

 Metcalf's studies, to which reference has already been made. 



The inability of their hosts, the frogs and toads, to endure salt 

 water makes their evidence as to land routes of dispersal peculiarly 

 cogent. Opalinids have remarkably clearly indicated phylogenetic 

 relationships (Metcalf, 1926), probably more clearly indicated than 

 in any other group of Protozoa. These two groups, the Anura and 

 their opalinids, are thus peculiarly favorable for studies by the host- 

 parasite method, especially studies of the phylogeny of the Anura and 

 of their geographic dispersal. 



The Ophryoscolecidae, a group of ciliates which live in the stomachs 

 or intestines of ungulates, anthropoid apes and some South American 

 rodents, have a highly diversified taxonomy, with relationships well 

 indicated, are almost world-wide in distribution and seem, from our 

 present inadequate knowledge, to be specific as to their hosts. They 

 and their hosts should furnish important host-parasite data. No 

 animals are better represented in fossil records than are the Ungulata. 



Among the flatworms the Temnocephaloidea, with the crayfish on 

 whose gills they are parasitic, have been used very effectively in host- 

 parasite studies by von Ihering and Harrison, as already noted. Von 

 Ihering and Johnston have made similar use of data from the flukes 

 (trematodes), the tapeworms (cestodes), and some of their hosts. 

 But the important results already obtained by aid of evidence from 

 the flatworms are but a very minor fraction of the harvest that may 

 be reaped by adequate study of this group. 



Darling's studies of the origin and spread of human races in the 

 light of their hookworm parasites are an example of the use of data 

 from round worms (Nematoda). Among the Nematoda there are 

 innumerable free-living forms, and great numbers of parasitic species 

 infesting almost all kinds of animals and very many kinds of plants. 

 A parasitic nematode is even known from a ciliate infusorian — a 

 metazoan parasite in a protozoon. There is in the parasitic members 

 of this group and their hosts a wealth of material which should prove 

 an inexhaustible mine for working by von Ihering's method. The 

 nematodes rival the trichonymphs of the termites as a source of data 

 for such use, indeed because of their universal abundance and the 

 huge number of their species they must surpass the trichonymphs in 

 the number and variety of problems their evidence will help solve. 



'Using Wenyon's (1926) modification of Aletcalf's name " protociliates ". 



