546 H. S. Jennings and George T. Hargitt. 



Popoff in his recent brilliant studies on various infusoria finds 

 frequent indications of the existence of diverse races of the same 

 species. Thus, in Frontonia, if a culture is started from a single 

 individual, the size is found to be more uniform than if started 

 from a number of individuals ('08, p. 269). This indicates of 

 course that among the original individuals there were hereditary 

 differences in size. In Stylonychia he finds that different cultures, 

 each derived from a single individual, show characteristic differ- 

 ences in mean size, and attributes this to hereditary differences 

 in the sizes of the original specimens from which the cultures 

 came ('08, p. 345). In the second of his " Zellstudien" ('09), 

 Popoff gives a number of examples of inherited differences in size 

 in Stentor and Frontonia, together with what he believes to be 

 the explanation of the origin of the differences. This explanation 

 we shall take up later. Of special interest is the indication of the 

 existence of different races of Paramecium, mentioned in the post- 

 script of Popoff 's paper ('09, p. 180). Study of the ratio of the 

 volume of the cytoplasm to the volume of the nucleus carried out 

 on Paramecium by three different investigators in the same lab- 

 oratory gave ratios in the different cases of 15 to 1, 30 to 1 and 45 

 to 1. These great differences naturally suggest that different 

 races of Paramecium were under consideration, and an investi- 

 gation of this possibility is promised us, by Rautmann. 



It is desirable that an investigation be made of the ratio of 

 nucleus to cytoplasm in the races described in the present paper; 

 this has not yet been done. 



McClendon ('09) observed in Paramecium the existence of a 

 number of races of diverse size, the relative sizes remaining the 

 same for long periods and under varying conditions of culture. 

 One of these had but one micro-nulceus, belonging thus to the 

 caudatum group, while two others had two micro-nuclei, and there- 

 fore belong to the aurelia group. The largest aurelia race ob- 

 served by McClendon was as large as the caudatum race, a result 

 never reached with the races cultivated in this laboratory. 



