THE HEREDITARY FACTORS AND DIFFERENTIATION 399 



itself with its axis along a radius of the centrifuge, and the stratified 

 distribution of its contents is accentuated. Further, the egg be- 

 comes flattened, and the cleavage-spindle, adapting itself to the 

 longest axis of available cytoplasm, lies horizontally instead of in 

 the vertical position. The result is a cleavage division in the vertical 



2-cell 

 taking 



Fig. 192 

 Cleavage and chromatin-diminution in the normal egg of Ascaris. i, 

 stage. The first cleavage is latitudinal; chromatin-diminution is 

 place in the animal cell. Si(AB), first somatoblast rudiment of the primary 

 ectoderm. la, Enlarged view of the diminution process. 2, 3, 4-cell stage; 

 2, T-shaped phase. 3, Lozenge-shaped phase. Note extra-nuclear chromatin 

 resulting from diminution in A and B. S.^ {EM Si), second somatoblast (endo- 

 meso-stomodaeal rudiment). 4, At the next cleavage, chromatin-diminution 

 occurs in the second somatoblast. 5, 6, Later stages. iSj , secondary and tertiary 

 ectoderm rudiments. P4, germ-cell with undiminished chromatin. (After 

 Boveri, from Jenkinson, Experimental Embryology , Oxford, 1909.) 



