562 



On the Synapsis in Amphibia. 



DESCRIPTION OF PLATES. 



[Figs. 2 — 22 are drawn with a 3-mm. long-tube Zeiss apochromatic 1*40 aperture, and a 



27 ocular.] 



Plate 20. 



Fig. 1. — Section of testis of Triton (June) as seen under a low power lens. At the upper 

 margin is the attachment between the testis and the body wall and the membrane 

 which surrounds the tubules. The foot-cells are not shown. Near tbe upper margin 

 to the right are two "male ova"; towards the left are tubules with cells in the 

 premaiotic (somatic) stage dividing at (b). The region marked (6) contains the zone 

 of transformation wherein the synaptic gemini are constituted. Late synaptic 

 (heterotype) prophases are seen at (c), and the first and second maiotic divisions 

 lower down. 



Fig. 2. — Cell from the upper premaiotic region, the nucleus showing bodies representing 



the 24 chromosomes while in a condition of complete rest. 

 Fig. 3. — Cell from the same region as fig. 2, viewed from a direction at right angles to the 



foregoing ; the bodies representing chromosomes seen end on. 

 Fig. 4. — Cell in the first phase of the synapsis, showing the bodies representing the resting 



premaiotic chromosomes uniting in pairs to form the gemini. 



Plate 21. 



Fig. 5. — Cell from the] same region as fig. 4, viewed from a direction at right angles 



showing the gemini end on. 

 Fig. 6. — Cell advancing in the synapsis, the gemini elongating. 

 Fig. 7. — Synapsis further advanced, the gemini elongating into loops. 

 Fig. 8. — Synapsis still further advanced, the gemini moving from their original central 



position. 



Fig. 9.- — The gemini becoming converted into loops. 



Fig. 10. — The gemini becoming polarised into the loops of the coarse spirem figure. 



Plate 22. 



Fig. 11. — Cell showing the coarse spirem, the threads not split. 



Fig. 12. — Same as fig. 11, but showing the first traces of the longitudinal split, 



Figs. 13, 14. — Longitudinal split more apparent. 



Fig. 15. — The split seen at its maximum. 



Fig. 16. — The split seen closing up at places. 



Plate 23. 



Figs. 17, 18. — Cells showing the ends of the loops with portions of the split closed up, 

 others open. 



Figs. 19, 20, 21. — Stages in the first maiotic division. 



Fig. 22. — The diaster of the first maiotic division, showing the split in the diastral 

 chromosomes. 



