60 Can Science Explain Life? 



protoplasmic needles called the aster, which ap- 

 pears to grow outwardly from a tiny central 

 region called the centrosome. The clustering of 

 the astral rays about common centers is in some 

 respects similar to the arrangement of the mole- 

 cules of a polar solute with the same ends toward 

 the solution, or to the radiating clusters of needle- 

 like crystals which are sometimes obtained by pre- 

 cipitation of certain substances, such as calcium 

 sulphate. Central bodies usually occur in pairs, 

 although four or more may occur in a single cell. 

 A constant circulation of fluid is maintained in- 

 wardly through the astral rays and outwardly 

 through the spaces between the rays, which is 

 probably the means employed for gathering food 

 material for growth. As these astral rays grow 

 longer and become more numerous they will be- 

 come more crowded in the region of the centro- 

 some, which probably causes the entire structure 

 to cave in and to divide into two separate centro- 

 somes. The rays from these two daughter cen- 

 trosomes will then grow and spread out in all 

 directions, and their subsequent movement away 

 from each other towards the opposite sides of the 

 cell may be due to their mutual encounters. That 

 the astral rays are rigid structures and not flex- 

 ible fibers under tension is proved by the fact that 



