EXPLANATION OF PLATES 
All the figures excepting figure 1 were drawn at the level of table with the aid 
of the camera under a Zeiss 1.5-mm. apochromatic objective and a compensating 
eye-piece no. 8 (tube length, 160 mm.). The combination affords a magnifica- 
tion 2350 diameters. 
ABBREVIATIONS 
c, centrosome p, perforatorium 
¢.1, proximal centrosome pr, proliferating region 
¢.2, distal centrosome p.spg, primary spermatogonium 
k, chromatoid body spc, spermatocyte 
m, mitochondrial body v, vesicle 
nt, nutritive cell 
PLATE 1 
EXPLANATION OF FIGURES 
1 Cross-section of the testicular tube, showing the zonal arrangement of the 
seminal elements; there are three zones in the figure; at the upper pole is the 
proliferating region. X 200. 
2 Secondary spermatogonia; in the cytoplasm are chromatoid bodies of vary- 
ing shapes and sizes. 
3 Primary spermatogonium. 
4and5 Equatorial plates of the spermatogonial mitoses, showing forty-eight 
chromosomes. 
6 Side view of the spermatogonial metaphase. 
A cluster of nutritive cells. 
8 Preleptotene stage. 
9 Leptotene stage. 
0 Synizesis stage. 
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