Plate XXI 



X 



X 



fl 



% T 



Four stages of the segmentation of the egg of Ascaris megalocephala uttFValens, 

 somewhat diagrammatic, after BOVERI (1903 a). 



a. Close of first division ; in the upper cell the long chromosomes are breaking 

 up into short units and throwing off the thickened ends. 



b. Anaphase of second division ; in the upper cell the thickened ends of the 

 chromosomes take no part in the mitosis. 



c. Four-cell stage with resting nuclei. 



d. Metaphase of third division, in the upper cells in face, in the lower cells 

 from the side. The left lower cell is undergoing "chromatin diminution." 



