EXPLANATION OF PLATES 
The figures in all the plates were drawn with the aid of the camera lucida, 
using in every case a Zeiss hom. imm. 1.5 mm. lens, the oculars varying according 
to the size of the cell. In figures 1 to 15, 22, and 27 to 35 a Zeiss compens. ocul. 
No. 12 was used, giving a magnification of 2950 diameters. The same combination 
was used for figures 16 to 21, 23 to 26, 39, 40, and 42 to 63, but they were subse- 
quently enlarged 13 diameters to work out details. Figures 36 to 38 and 66 to 
86 were made using a Spencer compens. ocul. No. 20, at a magnification of 3600 
diameters. Figure 64 was drawn with Spencer ocular 6. 
All figures have been reduced ¢ in reproduction. 
PLATE 1 
EXPLANATION OF FIGURES 
1to6 Nuclei of secondary spermatogonia showing individualized chromosome 
X in different conditions of condensation. 
7 The same chromosome drawn from three nuclei belonging to secondary 
spermatogonia. 
8and9 Early spermatogonial prophase showing chromatic bands. 
10 and 11 Two sections of two spermatogonia showing the orientation of the 
large chromosomes within the nucleus. 
12 Prophase in the spermatogonia of latter ener 
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