PLATE V. 



Note. — All drawings were made by the author, with the aid of a camera lucida. 

 A Bausch & Lomb one-twelfth-inch objective and one-inch eyepiece were used. 

 Length of tube, lG5mm.; camera lucida arm., 95 mm.; magnification, about 1000 

 diameters. Drawings not reduced in reproduction. 



Fig. 1. Early spermatocyte, showing small size of cell and relatively large size 

 of nucleus. 



Fig. 2. Later stage. The chromatin in the spireme condition. The cell has 

 grown somewhat and the amount of cytoplasm especially has increased. The 

 dark body at one side of the nuclear cavity is the accessory chromosome. 



Fig. 3. Considerably later stage. Cell has increased in size. The spireme is 

 broken down and stains diffusely. The accessory chromosome has increased 

 much in size. Yolk masses in a halo around the nucleus. 



Fig. 4. The j^seudo-gei'minal- vesicle stage. The chromatin, with exception 

 of accessory chromosome, arranged in a diffuse reticulum. The accessory 

 chromosome is at its maximum size and contains practically all the chromatin 

 of the nucleus. 



Fig. 5. The chromatin is reappearing in the form of tetrads. The accessory 

 chromosome has decreased much in size. Yolk mass at one side of nucleus. 



Fig. 6. Later stage in tetrad formation, showing several modifications of the 

 typical form. 



Fig. 7. Later prophase. Tetrads shorter and more massed. Accessory chro- 

 mosome plainly distinguishable. Centrosome first seen at this stage as a 

 dumb-bell-shaped figure in the mass of dentoplasm. 



Fig. 8. The centrosome has mov^d toward the nucleus. Astral rays have 

 formed. 



Fig. 9. The centrosomes have reached the membrane and, having separated, 

 have begun their migration apart. 



Fig. 10. Centrosomes still further apart. 



Fig. 11. Late prophase. The membrane has partly disappeared and the mantle 

 fibers are seen connecting the centrosomes and chromosomes. 



Fig. 12. Stage somewhat earlier than fig. 11. 



Fig. 13. Later stage, showing the short spindle. Chromosomes are arranged in 

 the equator. Astral rays are seen extending to th6 cell membrane. 



Fig. 14. The spindle has elongated and the chromosomes show signs of division. 



Fig. 15. Slightly later stage. * 



