398 BIOLOGY OF THE PROTOZOA 



this group from other ciliates as a sub-class Protoeiliata, while the 

 remainder of the great group of ciliated Infusoria were grouped as 

 Kuciliata. In this he has been followed by Doflein, Reichenow- 

 Doflein, Wenyon and the majority of protozoologists. Personally, 

 however, I cannot subscribe to this point of view; I am second to 

 no one in recognizing the superlative work of Metcalf on represen- 

 tatives of this group, but I do not agree to the separation of 4 genera 

 of astomatous forms as Prociliata from the number of other astoma- 

 tous forms, which, together with the hundreds of genera of mouth- 

 bearing forms of ciliates are placed in an equivalent group, the 

 Euciliata. Nor can I regard the so-called Protoeiliata as primitive. 

 The most generalized forms of free-living ciliates, with which the 

 Opalinidae agree in ciliation, are mouth-bearing forms, and the 

 absence of a mouth in parasites is much more probably a degenera- 

 tive than a primitive character, and is to be regarded as a special 

 adaptation to the conditions of a limited but highly nutritive 

 environment. 



Nor can the absence of dimorphic nuclei pass unquestioned. 

 The cell body of an opalinid is filled with discoidal structures which 

 were interpreted by Tonniges (1927) as representing a distributed 

 macronucleus similar in character to that of Dileptus gigas (Fig.25, 

 p. 52). The same point of view has been vigorously maintained 

 by Konsuloff (1922) but actual proof is still lacking. The history 

 of amicronucleate ciliates shows that dimorphic nuclei are not 

 essential for continued metabolism (see p. 225); here, however, the 

 diversity of chromatin in the opalinid nucleus suggests the correct- 

 ness of Tonniges' (1927) view that these nuclei possess both germ- 

 inal and somatic components. 



Finally the absence of conjugation and the substitution of gametic 

 fertilization is not unique with the Opalinidae. Here by repeated 

 division without intervening growth, gametes of different size (aniso- 

 gametes) are formed and these fuse in copulation. The same 

 phenomenon occurs in Glaucoma (DaUasia) frontata, a free-living 

 ciliate, the only difference being that the gametes are isogamous 

 and derived from the same parent (Calkins and Bowling, 1928). 

 Here fertilization is pedogamous while in Ichthyophthirius multi- 

 filius the process has apparently gone one step farther into autogamy 

 according to Neresheimer (1908) and Biischkiel (1910). 



The Opalinidae are parasites of frogs and toads primarily. Some 

 species occur in fish, and one, Protopalina nyanza, in a reptile. 

 They are represented, according to Metcalf, by 4 genera which 

 differ in form of the body and the number of nuclei. Protopalina, 

 Metcalf, and Zelleriella, Metcalf, have each 2 nuclei. Cepedea, 

 Metcalf, and Opalina, Purkinje, have many nuclei. Protopalina 

 and Cepedea are nearly circular in cross-section; Zelleriella and 

 Opalina are flat. 



