334 GERMINAL ORGANIZATION INDUCTION PHENOMENA 



Fig. 24. Effect of centrifugation on Barnea eggs stained in vivo by toluidine blue. In each egg, 

 the 3 zones obtained contain, from top to bottom, hpids, clear cytoplasm, yolk and a granules 

 (small dots). Upper row, moderate centrifugation. Lower row, stronger centrifugation. 

 Left, the egg during maturation; strong centrifugation reveals some [i-granules, lighter 

 than the cytoplasm; center, moderate centrifugation (above) leaves the ^-granules near the 

 pronuclei, while stronger force draws them between the cytoplasm and fat; right, the same 

 difference for the [3-granules embedded in the astral rays. From Pasteels and J. Mulnard, 



1957- 



Fig. 25. Experimental demonstration of the relation between the a- and p-granules in the 

 egg of Barnea. The initial staining was done as in the preceding case. Centrifugation was 

 applied shortly before the first division. At the Il-or IV-cell stage, the blastomeres show a 

 variable amount of a-granules (small dots). The amount of [i-granules formed (large dots) 

 is roughly proportional to the amount of the a-granules present in each cell. 



Fig. 26. Eggs of Portuguese oyster (Gryphaea angidata) stained as in the preceding cases 

 and submitted to centrifugation. (a) during maturation, with the a-granules driven to the 

 centripetal level of the yolk mass, and (b) during the pronuclei stage, with the ^-granules 

 which have been formed in the meantime and are driven, as in Barnea, to the interface 

 between the clear cytoplasm and the fat globules. From Pasteels and Mulnard, 1957. 



