ON THE STRUCTURE OF PROTOPHRYA OVICOLA. 119 



dye, but in unstained material it cannot be distinguished from the surrounding gran- 

 ules. It is always closely applied to, in fact flattened against, the macronucleus, 

 and might easily be overlooked. I have not always been able to find it, and have 

 obtained clearest demonstrations of its presence only with a T V apochromatic objec- 

 tive and ocular 12 or 18. In one instance (Fig. 7) the micronucleus lay in an inden- 

 tation on the ventral side of an anterior projection of the macronucleus. 



The only other species of the family which is known to possess a micronucleus 

 is Anoplophrya branchiarum Stein. In the possession of a micronucleus and in the 

 spherical form of the macronuclus Protophrya is the most primitive genus of the 

 family, retaining these characters as they appear in many holotrichous forms not 

 modified by parasitism. 



Two cases of transverse division of the normal type have been observed in the 

 material at my disposal. Conjugation, encystment, and spore formation have not 

 been detected. 



The systematic position and relationships of Protophrya are patent. The char- 

 acter of the ciliation and the absence of mouth and anus place it unquestionably 

 in the Opalinidse. The following table adapted from Schewiakoff ('96) will serve to 

 locate the new genus Protophrya in this family. 



KEY TO THE GENERA OF THE OPALINID^. 



With a single contractile vacuole posterior to a spherical nucleus Protophrya. 



With one or two rows of contractile vacuoles or with longitudinal excretory canals. 1. 



Without contractile vacuoles 3. 



1. Without suckers, hooks, or internal rods; one or two rows of contractile vacuoles; 

 nucleus long, cylindrical Anoplophrya. 



1. With suckers, hooks, or internal rods 2. 



2. With one or two hooks on anterior end or with internal rod; one or two rows of 



contractile vacuoles; nucleus long, cylindrical Hoplitophrya. 



2. With suckers on anterior end; longitudinal contractile canal; nucleus ellipsoidal 



or reniform Discophrya. 



3. Body vermiform or oval; single long ribbon-like nucleus or many nuclei irregularly 



contoured Opalinopsis. 



3. Body flattened, asymmetrical; many round nuclei or a single bipartite nucleus. 



Opalina. 



The primitive condition of the contractile vacuole, the spherical macronu- 

 cleus, and the absence of special structures such as the hooks or internal rods 

 of Hoplitophrya stamp this new genus as one of the least specialized members 

 of the family. The presence of a micronucleus may also be regarded a primitive 



