MORPHOCHORETIC PATTERN 



CLEAVAGE 



335 



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-A 



li-^ 



■A 



Fig. 27. The a-fi granules of sea-urchin eggs, revealed by centrifugation. a, b, c : eggs stained 

 in vivo, centrifuged, fixed in Izquierdo's mixture and mounted in toto; a, h, eggs centrifuged 

 some minutes after the staining, and showing the a-granules; in a, centripetal side on top, 

 centrifugal down ; in b, the egg is seen from the centrifugal side. The clear centrifugal cap is 

 extremely rich in RNA and contains the majority of mitochondria. The a-granules 

 form a girdle between this cap and the yolk platelets; in c, the egg has been centrifuged 

 at the streak stage, the lower cap and the a-granules, scattered among the yolk, are visible, 

 while the fi-granules form a dense layer under the hyaline layer with the pronuclei; d, a 

 section of similar eggs, fixed in formol saline and stained with Alcian blue at pH i ; selective 

 staining of p-granules ; e, f, acidic phosphatase revealed in the ^-granules (whole mounts) 

 at the I- and 2-cell stages. From Pasteels, 1958. 



Literature p. 483 



