466 



DAVID H. DOLLEY 



lated and the results are here represented in a graphic way by 

 the frequency-polygon of text figure A. 



It is sufficient to say that there is nothing to distinguish one 

 series from another in the way the figures run. They are dis- 

 persed above or below the same median. Sixty-six per cent of 

 all cells fall within two units of the common arithmetic mean. 

 The tendency toward constancy is the more remarkable, outside 

 of the nmnerous chances for variation which will be mentioned, 

 because the length of the third diameter, the depth of the cell, 

 must in such measurements as these be assumed to be equal 



Text fig. A Frequency-polygon of 250 cells 



to the transverse diameter of the cell section. Though this un- 

 known diameter is probably fairly uniform, it is one of the factors 

 of dispersion that must be smoothed out by averages. In the 

 measurements of the crayfish for example, where the third di- 

 mension was actually approximated, though the transverse 

 diameters of cells are frequently unequal, the standard deviation 

 was represented by smaller figures, ±1.3 and ± 1.65. 



The most important point in explanation of why the figures 

 for the nucleus-plasma coefficients are so constant is as follows: 

 The nucleus-plasma coefficient of the resting cell holds to the 

 same figure throughout the first stage of activity when that 

 resting cell is excited to activity. That is, though both cells 

 and nuclei increase in size, they increase in exactly the same 

 proportion. In the Purkinje cell this has been true for an in- 



