Spirazines 47 



pear to be formed de novo from cytoplasmic 

 material and usually occur in pairs, although four 

 or more may occur in a single cell. A constant 

 circulation of fluid is maintained inwardly 

 through the astral rays and outwardly through 

 the spaces between the rays, which is probably 

 the means employed for gathering food material 

 for growth. 



The clustering of the astral rays about common 

 centers may be due to conditions similar to those 

 which cause the molecules of a polar solute to 

 arrange themselves with the same ends toward 

 the solution. As these astral rays grow longer 

 and become more numerous they will become 

 more crowded in the region of the centrosome, so 

 that the entire structure will eventually become 

 unstable, will cave in, and two separate centro- 

 somes will make their appearance. The rays 

 from these two daughter centrosomes will tend to 

 spread out in all directions and as a result of 

 their mutual encounters will cause the two new 

 asters to move away from each other and towards 

 the opposite sides of the cell. 



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