330 



GERMINAL ORGANIZATION 



INDUCTION PHENOMENA 



Fig. 21. Toluidine blue metachroniasia in the 8-cell stage of the rat. The eggs stained in 

 vivo have been fixed by a special mixture (Izquierdo, 1955) which preserves the stain. 

 (a) A/;/flc«/a-like specimen, with the larger cells below and left, the smaller ones above and 

 right (2 out of focus). See the dark masses of MPS-loaded granules, especially developed 

 in the large cells. The symmetry pattern is apparent, (b) A less flattened specimen. The 

 large, enveloping cells are numbered i to 4; their columns of metachromatic granules 

 are conspicuous. The smaller, embryonic cells (only 3 visible, i out of focus) contain fewer 

 of these organelles. Photographs of Izquierdo, 1955. 



