Blackhan. — Spermatogenesis of Scolopendra. 



PLATE 2.— Continued. 



Fig. 19. Various appearances presented by the karyosphere : a, in preparations 

 not sufficiently decolorized ; b, where the chromatin threads have 

 been massed together irregularly by the fixing fluid ; c, section through 

 one side of the karyosphere ; d, e, thin, well-stained sections showing 

 the true spireme character. 



Figs. 20-22. Early prophases showing the behavior of the centrosomes. In Figure 

 22 is shown a section through one side of the karyosphere. 



Figs. 23,24. Nuclei in later stages, showing the origin of the chromosomes from 

 the karj'osphere. A number of chromatic segments have already 

 become detached and have undergone the early processes of tetrad for 

 mation, while others are still connected with the karyosphere. 



Fig. 25. Later stage. The last chromosomes are now leaving the karyosphere, so 

 that nothing of this remains except the accessory chromosome. 



Figs. 26, 27. Nuclei showing the tetrads derived by a longitudinal and a cross 

 division of the chromatin segment. The karyosphere is much reduced 

 in size, but still contains several chromosomes. In Figure 26 the 

 accessory chromosome is readily distinguished. 



Fig. 28. The tetrads are becoming condensed, but many still show the two 

 divisions. 



Fig. 29. Late prophase. The chromosomes have become still more condensed, 

 and are now homogeneous. The accessory chromosome is distinguish- 

 able from the others by its shape. The centrosomes are at opposite 

 sides of the nucleus. 



Fig. 30. Still later prophase. The nuclear membrane is breaking down. 



Fig. 31. Very late prophase. The nuclear membrane has disappeared and the 

 spindle is being formed. 



Fig. 32. Metaphase. The cell outline has become oval, and the spindle still 

 extends across the shorter diameter of the cell. The cytoplasm in 

 the region of the astral system is more open than in the peripheral 

 region. 



