117 



feature of these phenomena is the presence of one or two refractive and 

 deeply staining disc-shaped masses in the nuclei. I find either one or 

 two of these masses in the nciclei of the minute animals before encyst- 

 ment, one or two in the nuclei of the cysts in the frog's rectum, one or 

 two in the nuclei of the cysts in the water, one or two in the nuclei of 

 the cysts in the tadpole, one or two in the nuclei of the little Opalinae 

 after hatching, and I have sometimes found what appear to be similar 

 bodies in the nuclei of gametes during conjugation. If these masses are 

 extruded into the cytoplasm, and some of my preparations seem to in- 

 dicate that they are, the time of their extrusion seems to vary within 

 wide limits. When two nuclei are present in the cysts or minute forms 

 of any of these species, either nucleus may have none, one or two of 

 these masses. When more than two nuclei are present (0. dimidiata)^ 

 any of these nuclei may have none, one or two of the chromatin masses. 

 It is seen that I do not find the phenomena quite so definite as Neres- 

 h e im er describes. I have not yet, however, studied sections of these 

 forms. 



No complete degeneration of nuclei occurs in the binucleated 

 Opalinae in connection with the spring reproduction, at least before 

 conjugation, and I have seen nothing in any species to indicate that 

 new nuclei are formed from chromatin masses extruded from the old 

 nuclei into the cytoplasm, as Neresheimer describes. The nearest 

 approach to this I have seen is the appearance of the cytoplasmic sphe- 

 rules with their peripheral granules, but these appearances are found 

 throughout the year and are not connected with the formation of new 

 nuclei. In certain abnormal Opalinae obtrigonae I have found many 

 of the nuclei degenerating. Some of my preparations of 0. dimidiata 

 give some indication of a somewhat similar degeneration of some of the 

 nuclei before and during the spring reproduction, but I have found 

 nothing to suggest that many of the nuclei degenerate. I am not at all 

 sure that any do. The question must be carefully studied upon sections. 



Infection experiments. 



Under natural conditions the several species of Oimlina are found 

 only in certain definite hosts. The hosts and parasites I have studied 

 are related as indicated in the following table : 



Host. Parasites. 



Rana esculenta Opalina dimidiata 



xelleri 

 Rana fusca . - rauarum 



Hyla arborea - obtrigona 



