THE OPALIXID CILIATE IXFUSORIAXS. 325 



phase of the life cycle of the parasite is not confined to any one 

 season of the year. So P. satumuUs, while seemingly more nearly 

 related to the caudata group than to any other, may hardly be 

 placed in this group. Its occurrence in a marine fish tempts one 

 to speculate, but there is little profit in recording such speculations. 

 Leger and Dubosc, the discoverers of this very intesesting species, 

 thought that because of its habitat it is probably the most primitive 

 of the Opalinidae, but this belief seems hardly borne out by wider 

 comparisons among the much larger number of species now known. 

 I do not see that there are any data to indicate how Box, a marine 

 fish, came to be infested with a Protoopalina. 



Frotoopalina mossamhicensis (p. 73), from an East African Rana, 

 seems rather widely separated from any other Protoojmliiia. Pro- 

 toopalina primordiaKs is not sufficiently described to be included in 

 our discussions. 



The genus Protoopalina is so widely distributed geographically, 

 and is known from so wide a range of hosts, that the original hosts 

 can not readily be determined. They were probably present in the 

 earliest Anura, for they are now known from all families of Anura, 

 But this fact is hardly conclusive, since it is possible that some 

 families bear adopted species rather than species which arose in the 

 present hosts or their ancestors. This is certainly true as to the 

 derivative genera ZeUerlcIJa, Cepedea, and Opalina and may be true 

 of Protoopalina. We do find indications, as noted above, of the place 

 of origin of some of the subgeneric groups of species of Protoopalina^ 

 and so have placed the origin of this old genus in Equatoria, the 

 continent formed by the union of two previous land masses, Gond- 

 wanaland to the east and South Atlantis on the west, but we do not 

 laiow the character of the earliest Anura in Equatoria in the Tri- 

 assic or perhaps earlier period, when the Opalinidae first appeared. 



Our conspectus of the occurrence of the Protoopalinas in their hosts 

 fails to show any general limitation of closely related parasites to 

 closely related species of hosts, though when later we view the 

 family Opalinidae in a broader view we shall see some general host- 

 parasite relations. Protoopalina is a very old genus and has had time 

 to become adapted to diverse hosts. In this regard it is in sharp con- 

 trast to the genus ZelUriella. In my early studies of the Opalinidae 

 I found it possible to infect almost any of the European species of 

 Anura with cysts of almost any species of European Opalinid (see 

 Metcalf, 1909), producing thus many sorts of infection not known 

 in nature. These Opalinids in their unaccustomed hosts lived and 

 thrived for some months. Their ultimate fate was not observed be- 

 cause the tadpoles could not readily be brought back alive with me 

 from Bavaria to this country. One suspects that such unaccustomed 

 infections may occur in nature, but fail to become permanently estab- 



