SPECIES IDENTITY OF NUCLEUS-PLASMA NORM 455 



structions were made from two plates, so that the factors of 

 possible variation involved in the thickness of the plates and the 

 magnification are constant within each set and are shown to be 

 of very minor importance (table 2). 



In other respects the technical procedures were the usual 

 ones. Sixteen cells were reconstructed, eleven from two micra 

 serials and five from one micron, with one repetition. Number 

 one was a trial cell for various points of technic and hence is not 

 included. Figures 1 to .5 illustrate the various types of cells. 



When each cell was completed to the point of being ready 

 to have the straight edges of its component layers smoothed down 

 to a curved surface, the plasma and the nucleus were weighed 

 separately on the theory that the quantitative relations of their 

 prototypes would be preserved. 



b. By application of the prismoid formulas. The data ob- 

 tained for wax reconstruction are suitable for the application 

 of Simpson's Rule or some form of the Simpson-Lagrange Ap- 

 proximation derived therefrom to determine the volume. No 

 mathematical discussion will be attempted and for the statement 

 of the formulas the reader is referred to any standard work on 

 calculus (in the calculus by Davis-Hedrick on pages 129, 240 and 

 tables 45). The area of each layer can be exactly determined, 

 and the thickness of the layer, the number of layers, and the 

 number of planes of section are known. The area was found 

 by using a polar planimeter on the original camera lucida tracings.. 

 The number of planes of section is one greater than the number' 

 of layers, that is, the outermost extremity, of one end layer was 

 counted as one area, while the estimated area of the opposite 

 extreme end layer, usually of very diminished size, was taken as 

 the closest approximation of the other area. The actual 

 procedure, while tedious, is very simple. 



The results in the case of the one micron sections are so con- 

 sistent with those obtained by weighing the wax models that 

 there is every indication of exactness (table 3). The results 

 in the case of the two micra sections are more variable, which 

 will be explained in the section on "Technical factors." By 

 way of further checking up the results, since the mathematically 



