CLEAVAGE AND DIFFERENTIATION 85 



normal cleavage. As already mentioned (p. 43), these facts prove 

 that during cleavage the nuclei divide in such a way that their 

 daughter-nuclei are quantitatively and qualitatively equal. 



A more recent and very elegant demonstration of the equivalence 

 of the nuclei of the blastomeres was carried out as follows. By 



7S 



SB 



Fig. 36 

 Diagram to show the altered distribution of nuclei in frogs' eggs made to segment 

 under pressure. A, Normal eggs. B, Eggs subjected to pressure. Left, 8-cell 

 stage; right, i6-cell stage. In each case a polar view is shown above, a side view 

 below. Cells produced by the division of corresponding cells are numbered alike. 

 (From Wells, Huxley and Wells, The Science of Life, London, 1929.) 



means of a fine hair, the fertilised egg of the newt can be con- 

 stricted into the shape of a dumb-bell, in such a way that the zygote 

 nucleus is confined to one side. This side will then undergo cleavage 

 as the nucleus divides, while the other side of the dumb-bell will 

 remain uncleaved. By releasing the ligature, the constriction can 

 be relaxed, and one nucleus — any one, at random — may be allowed 



