PLATE 9 



EXPLANATION OF FIGURES 



75 Side view of four-cell embryo showing diminution divisions in the daugh- 

 ter cells of the first soma cell, the latter having failed to undergo 'diminution' 

 at its first division. The stem cell is sir p. (X 1000) 



76 Top view of 'lozenge-shaped' four-cell embryo, showing polar views of the 

 'diminution spindles' in the daughter cells of the fii'st soma cell. Second soma 

 cell at so., and the stem cell at strp. (X 1000) 



77 Side view of the 'diminution spindles' in the daughter cells from the first 

 soma cell. (X 1000) 



78 Six-cell embryo, showing the nuclei of the soma cells which have under- 

 gone 'diminution,' and the stem cell (strp.), which is dividing by ordinary mitosis. 

 Extruded mass of chromatin lying free in cytoplasm of the soma cells. (X 1000) 



79 Six-cell stage, showing the stem cell with the diploid number of dyad 

 chromosomes, while the soma cells have all descended from cells which have 

 undergone 'diminution.' (X 1000) 



80 Six-cell embryo in which a "diminution division" is occurring in the second 

 soma cell (so.), and a normal mitotic figure in the stem cell (strp.). (X 1000) 



81 Median section through an eight-cell embryo, showing at the right the 

 stem cell, in which a 'diminution division' never occurs. (X 1000) 



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