B. F. Kingsbury 133 



Fig. 4. Spermatocyte. Transection of the nucleus when growth is 

 nearly completed. Most of the chromosome-loops are cut twice. 



Fig. 5. Spermatocytes. Growth nearly completed. Three cells are cut 

 nearly "longitudinally "; one cell shows the idiozome but not the nucleus. 

 The chromosomes are in the form of looi^s with their free ends toward 

 the idiozome. This is about the same stage as Fig. 4. 



Fig. 6. Splitting of the chromosome threads in two adjacent cells. 

 Chromosomes have lost their orientation in relation to the idiozome. 

 Splitting in some of the threads is not continuous. 



Fig. 7. Three Spermatocytes, showing ring-formation; some of the 

 chromosomes are twisted as 8's; while fragments only of others are seen. 

 But one cell is cut in the right plane to show the idiozome. The two 

 centrosomes are yet close together. 



Fig. 8. Spermatocyte. Section at the beginning of spindle-formation. 

 The centrosomes within the idiozome have moved slightly apart and faint 

 radiations have appeared. The chromosome rings are situated super- 

 ficially under the nuclear membrane and are cut irregularly. 



Fig. 9. Spermatocyte. Stage slightly older than that of Fig. 8. Kadia- 

 tions are more distinct and penetrate the' idiozome. Centrosomes naore 

 distinct. Chromosomes near the nuclear membrane. 



Fig. 10. Stage older than Fig. 9. Two cells are shown with young 

 spindles forming. The outline of the idiozome is still preserved. Note 

 the angle of the spindle axis. The nucleus of one of the cells is cut 

 superficially, and the chromosome forms are well shown. In the other 

 cell, the chromosonQes are on the side of the nucleus toward the idiozome. 



Fig. 11. Spermatocyte. Later stage; spindle well formed, with but 

 two chromosomes shown at the level. 



Fig. 12. Spermatocyte. Deeper section of the same cell shown in Fig. 

 11. Ring chromosomes are w^ell shown. Note their shape and bending. 

 Two Y-shaped chromosomes are shown. 



Fig. 13. Spermatocyte. Spindle at a later stage. The chromosomes 

 are being arranged on the spindle. The rings are bent in a typical 

 manner. 



Fig. 14. Spermatocyte. " Equatorial plate " stage, showing a typical 

 spindle. The chromosomes are breaking apart in the equatorial plate. 

 Fused ends of some of the chromatin loops are seen projecting. 



Fig. 15. Spermatocyte. An oblique polar view of the daughter-chro- 

 mosomes as they pass to the pole, showing the second splitting. 



Fig. td. Spermatocyte. Late anaphase. The chromosomes approach- 

 ing the poles. 



Fig. 17. Spermatocyte. Telophase. The chromosomes have become 

 closely massed; a vacuole caps the mass. Mid-body and remains of the 

 spindle are shown. 



Fig. 18. Spermatocyte. At the beginning of the growth period, with 

 the nucleus in a " contracted " condition. The chromatin is in a dense 

 mass, still connected with the nuclear membrane by strands. Detail of 

 structure in tlie nucleus cannot be made out. 



