368 E. Newton Harvey 



negative regions. When the micromeres are formed the pigment 

 is prevented from entering them by the large and prominent 

 asters, then present. Even when cut off from the pigmented 

 area of centrifuged eggs these cells are relatively free of pigment.^* 

 The granules are thus repelled by the centrosomes. If an increase 

 of permeability is the change initiating the development of an 

 unfertilized egg the same potential differences (between exterior 

 and interior, and different regions of the cell) might be expected 

 that takes place in muscles during stimulation. These potential 

 differences are quite general in the functioning of various tissues 

 (nerves, glands, sensitive plants, etc). Their origin is most 

 easily accounted for by variations in differential permeability 

 of the cell to anions and cations." Lillie^' has discussed this 

 theoretically in a recent paper. Without going into details it 

 may be said that "with the appearance of an increased permea- 

 bility the peripheral regions of the protoplasm must become, for 

 a time at least until the potentials are equalized, positive relative 

 to the interior." Such pigment granules if negatively charged 

 would be drawn by the electrostatic attraction of the now positive 

 egg surface, to the surface, providing of course, the potential 

 difference were high enough. A calculation (by Lillie) of this 

 based on the observed changes m muscle cells has given a value 

 of 14 volts per cm. This would be ample to account for the migra- 

 tion actually observed in Arbacia eggs. 



The orientation of small particles with relation to the asters 

 occurs in other eggs. Fischel^^ in staining sea-urchin eggs with 

 intra-vitam dyes noted a migration of particles stained with 

 neutral red, toward the nucleus and aster, the formation of an 

 ellipse about the spindle-figure and a ring about each daughter 

 nucleus where the cell divides, and finally, during the resting 

 stage, even redistribution throughout the cytoplasm. This pro- 

 cess is repeated during each cell division. 



''Lyon, E. P.: Arch. Entwm., 23, p. 67. 1907. 



'* See Bernstein, Arch. f. d. ges. Physiol. 1902, xcii, and Brunings, id. xcviii, and c. 1903. 



" LiUie, R.9: Biol. Bull, xvii, p. 207-208, 1909. 



'* Fischel, A.: Anat. Heftc, 37, p. 863, 1899, a'so Arch. Entwm., xxii, p. 526, 1906. 



