EXPLANATION OF PLATE III 



FIG. ii. X I .5- Later stage. Chromatin segments have broken into a num- 

 ber of small fragments. These are beginning to contract to form tetrads. 



FIG. 12. X 1.500- Entire cell during mid-prophase. Chromatin in the form of 

 cross-shaped tetrads. Centrosomes in the cytoplasm midway between nuclear mem- 

 brane and the cell-wall. 



FIG. 13. X I >5- Later stage. Tetrads more contracted. Linin net work be- 

 ginning to break down into more definite, less branched fibers. 



FIG. 14. X I >5- About the same stage. Tetrads in various stages of advance- 

 ment. 



FIG. 15. X I .5- Later stage, shortly preceding the breaking down of the 

 nuclear membrane. Chromosomes are nearly all homogeneous, but still preserve 

 their tetrad outline. Nucleolar part of karyosphere still intact. 



FIG. 16. X 1 ) 000 - Very late prophase. Nuclear membrane has disappeared and 

 spindle is forming. Chromosomes have changed from tetrad to dumb-bell shape. 

 Nucleolar remains of karyosphere grouped irregularly in the cytoplasm about the 

 centrosomes. 



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