ORIGIN OF THE CENTROSOME. 



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rests directly on the surface of the nuclear membrane (Fig. 8). 

 The new fibrils which proceed from the centrosome press on 

 the nuclear membrane or break through it, and eventually form 

 the spindle of the caryokinetic figure. 



The same interpretation may be applied to those cases where 

 the centrosome divides at some distance from the nucleus 

 (Fig. 9). Each daughter centrosome spins out the cytoplasmic 

 filaments, forming a small spindle between them. Thus the 

 formation of the centrosome by the ends of the aster fibrils, 



Fig. 8. — Blastomeres from the central portion of the blastodisc of Loligo. The segments i, 2, 

 3, 4, 5, etc., show different stages in the formation of the spindle fibrils from the centrosome. 



and the production of the group of filaments from the centro- 

 some, are phenomena parallel with those seen in the thread 

 and varicosities in the striated muscle cell during the alternat- 

 ing phases of contraction and expansion. 



Viewed in this way, the function of the aster and centrosome 

 falls under two heads : — 



(i) By the radial arrangement of the cytoplasmic filaments, 

 and the consequent condensation of the cytoplasmic substance 

 in a definite place, the cell is able to produce the filaments in 



