288 NATHAN FASTEN. 



EXPLANATION OF PLATES. 



The figures in the accompanying plates were drawn with the aid of the camera- 

 lucida at a magnification of 1,600 times. The}' are all from smear preparations. 



EXPLANATION OF PLATE I. 

 FIG. i. Resting primary spermatogonium. 



FIG. 2. Fragmentation of chromatin into smaller clumps, primary sperma- 

 togonium. 



FIGS. 3 TO 7. Nutritive cells. 



FIGS. 8 TO ii. Secondary spermatogonia in various stages of mitosis. 



FIG. 12. Resting primary spermatocyte. 



FIGS. 13 AND 14. Early growth stages, primary spermatocyte. 



FIG. 15. Leptotene stage, primary spermatocyte. 



