PLATE 25 



All the figures are drawn at tlie same magnification (x 2350) with a 

 Spencer 2 mm. objective, a Zeiss No. 12 compensating ocular, and an 

 Abbe camera lueida. Eeduced magnification on plates, 1700 diameters. 



Kg. 1. Spermatogonium in the equatorial plate stage, showing 

 twenty-three chromosomes. Fixed in Zenker's fluid and stained with iron- 

 alum haematoxylin and orange G. 



Fig. 2. Same stage as above but with the usual number of chromo- 

 somes (twenty-eight). Zenker's fluid, iron-alum haematoxylin, and orange 

 G. 



Fig. 3. Spermatocyte before the beginning of polarization. Fixed in 

 Zenker's solution and stained with phosphotungstic acid haematoxylin. 



Fig. 4. Spermatocyte at the beginning of polarization showing V- 

 figures. Zenker 's fluid and phosphotungstic acid haematoxylin. 



Fig. 5. Spermatocyte with short-stemmed Y-figures. Phosphotungstic 

 acid after Zenker's fluid. 



Figs. 6 and 7 illustrate successive steps in the pairing of the threads. 

 The section from which Fig. 6 was taken was fixed in Zenker's solution 

 and stained with phosphotungstic acid haematoxylin. Figure 7 was taken 

 from material fixed in Bouin 's fluid and stained with iron-alum haema- 

 toxylin. 



Fig. 8. A lateral view. Loops completed. Zenker's fluid and phos- 

 photungstic acid haematox^'Iin. 



[526] 



