xgoS] JENNINGS— HEREDITY IX PROTOZOA. 409 



In Other cases there was more variation in size among the dif- 

 ferent sets of progeny of D, particularly if the measurements were 

 made after but few fissions had occurred. But sometimes the 

 progeny of the large specimens were smaller, sometimes larger, than 

 those of the small specimens. On the whole, both large and small 

 specimens produced progeny of about the mean size for the group, 

 under the given conditions. 



Thus it is apparent that the differences in size shown within 

 such a polygon as D, Diagram i, are not due mainly to hereditary 

 internal factors. Before we can determine with certainty whether 

 any such factors are involved, we must make an analysis of the 

 variation polygon, determining so far as possible the different fac- 

 tors, external and internal, which go to make it up. 



7. Proposed Analysis of the Polygons of A'ariation. 



Our present task is then to determine, so far as possible, what 

 factors produce such polygons of variation as are shown in Dia- 

 gram I ; to define what the individuals of different sizes and propor- 

 tions really are, and to what their particular characteristics are due. 



There are several sets of problems to be considered; these we 

 ma}" classify as follows: 



1. AMiat are the causes and the significance of the variations 

 shown in a single variation polygon, such as D, Diagram i ? Why, 

 in a group of Paramecia grown under the same conditions, and 

 perhaps all descended from the same ancestor, do certain indviduals 

 show the mean length, while others are larger and others smaller? 

 Each size must have its determining factors. 



2. In different polygons from Paramecia of the same general 

 group and even when all are progeny of the same individual, the 

 mean size differs much. Thus, in Diagram 6 (page 470) the mean 

 length for polygon 8 is 146.108 microns; for polygon 11 it is 191. 360 

 microns, though both represent descendants of the individual D, of 

 the caiidatum group. \\'hat are the causes of such variations in 

 mean size among dift'erent sets of individuals? 



3. In diff'erent sets of individuals belonging to the same general 

 group, or descended from the same individual, the amount and range 



PROC. AMER. PHIL. SOC. XLVII. I90 AA, PRINTED JANUARY S, igcQ. 



