FACTS 



225 



the nuclear protoplasms ; and this transformation is further 

 manifested by the disappearance of the nucleus membrane, 

 that is, of the surface separating the nucleus from the cy- 

 toplasm. From this moment the substances of the nucleus 

 are, so far as their equilibrium goes, subjected to certain 

 actions coming from the cytoplasm. It is precisely these 



A 



FIG. 20. FIRST PHENOMENA OF KARYOKINESIS (FROM WILSON). 



cytoplasmic actions which present an interesting bipolar 

 character. 



At the beginning of karyokinesis there appears in the 

 cytoplasm, close to the surface of the nucleus, a little granule 

 surrounded by a light aureole ; this granule is called cen- 

 trosome and almost at once divides in two (Fig. 20, A). 

 Then the two centrosomes separate one from another, fol- 

 lowing the outer surface of the nucleus (at this stage the sur- 



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