12 Proceedings of the Royal Irish Academy. 



EXPLAITATION OP PLATES I. and II. 



[Figures 1-11 all camera liicida drawings ; magnification, 1000 diameters.] 



Figures. 



1. Cell with nucleus in dolichonema stage. 



2. Cell with, nucleus in strepsinema stage. 



3 and 4. Formation and thickening of chromosomes. The primary 

 chromosomes are cross-hatched in different directions. 



5. Polar view of the nuclear plate. 



6. Equatorial view of the same. 



7. Chromosomes leaving the nuclear plate. On the right the 



lateral displacement of the daughter chromosomes relative 

 to one another is shown. 



8. Daughter chromosomes approaching the poles. 



9. Portions of the strepsinematous thread. 



10, Tangential section of a nucleus showing the looping of the 



dolichonematous thread to form the strepsinematous con- 

 dition. 



11. Oblique view of a nuclear plate showing the connexion of 



each primary chromosome with each pole. 

 12 to 18. Diagrams to illustrate the behaviour of the chi'omosomes 

 during the first mitosis of the spore-mother-cells. 



