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H. B. GOODRICH 



intensely and show clear outlines under the highest magnifica- 

 tions. A 1.5 apochromatic objective, a no. 18 compensating 

 ocular were used and projections made with a camera lucida. 

 Optical cross sections through the center of the nucleus, i.e., 

 such as seen when the disc is observed edgewise were used for 

 measurements as such a section gives data for three dimensions 

 and thus the volume may be computed. To obtain such sec- 

 tions those nuclei were selected which when viewed edgewise 

 were not displaced in apparent position by change of focus, 

 (indicating that the two lateral faces of the disc were parallel 

 to the optical axis) and the greatest optical section thus presented 



Text fig. D Optical cross-sections of miclci from the two modal classes. 



by each nucleus was projected by camera lucida and outlined. 

 Examples of such projections are shown in text figure D. The 

 length and breadth of these figures were measured by rule to 

 half millimeters. Lengths varied from 13 nmi. to 22 mm. and 

 breadths from 5 mm. to 9 mm. From this data index figures 

 proportional to the volume were computed. The radius of the 

 disc is obviously one half of the length of the projection and this 

 squared and multiplied by the breadth gave the index figure. 

 The result is shown in the graph (text fig. E) . Vertical distance 

 indicates the number of nuclei measured and horizontal distance 

 the nuclear volumes in terms of the index figures. The curve 

 is clearly of bimodal nature showing that two types of sperma- 

 tozoa were present. Taking 375 and 525 as modal points we 

 have the proportion 375 : 525 : : 15 : 21 and it will be recalled 



