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EXPLANATION OF PLATES 



The drawings were made with a camera lucida at an original magnification of 

 2800 diameters, except figure 1, which was at 880 diameters. Ihey were then 

 enlarged by projection and worked over for details. In reproduction they have 

 been reduced to the magnification indicated. The photo-micrographs were made 

 with a Bausch & Lomb fiuorite system 1.9-mm. oil-immersion objective, N. A. 

 1.32, Zeiss 2 or 4 projection ocular, and Watson holoscopic oil-immersion conden- 

 ser, with the exception of figure 46; which was made with a Zeiss 4-mm. objective, 

 the other lenses as above. The photographs have been reproduced at the original 

 magnifications. The unit of magnification is 1400 diameters except for Plate 2 

 and fig. 46. Fixation was by 'B-15' unless otherwise specified. 



PLATE 1 

 explanation of figures 



1 Portion of wall of tubule of 50-day rat. Crt., chromatoid body; Id., idio- 

 some; M.I., inembrana limitans; Nu., nucleolus; P.c, pachytene cell; Sptd., 

 spermatid; X, accessory; L.c, leptotene cell. X 2100. 



