392 RALPH S. LILLIE 



formed by the assumed diffusion-fields having an orienting 

 influence on the colloidal particles and determining their fusion 

 along the radiating lines of force to form strands. The initial 

 appearance of a general centrally directed cytoplasmic radiation 

 in artificially activated sea-urchin eggs^- suggests that a change 

 of surface-permeability is adequate to produce this effect. 



Other factors, however, undoubtedly enter in the production 

 of cytoplasmic radiations, and the conditions are probably 

 too complex for satisfactory analysis at present. The dividing 

 cell, like iiritable elements in general, no doubt reacts as a whole 

 to changes in the electrical polarization of its surface; and cer- 

 tain localized metabolic changes (oxidations, etc.) presumably 

 result, whose position and character depend on the nature, 

 distribution, and physical conditions of the various substances 

 present — i.e., on the pre-existing cell-organization. Cytological 

 observation indicates that in dividing cells certain regions or 

 foci of active chemical change (centrosomes) make their appear- 

 ance, and become the centers of astral radiations; there is evi- 

 dence that the material forming such centers persists in the 

 interkinetic periods and becomes active only at certain times; 

 these times, judging from the above observations, appear to be 

 those when the cell-surface is undergoing the changes .prepar- 

 atory to division. It is possible that the change of surface- 

 polarization (which is equivalent to stimulation) initiates oxi- 

 dation-processes in each such area and leads to the formation 

 of acid metabolic products; on account of the high migration 

 rate of the hydrogen ion, each such area would then become neg- 

 ative relatively to adjoining regions; the radiations would thus 

 be the expressions of localized potential-gradients resulting from 

 the diffusion of electrolytes from chemically active regions; 



*^Ci. Wilson, Arch. f. Entwicklungsmechanik, 1901, vol. 12, p. 539; Hindle, 

 ibid., 1911, vol. 31, p. 145; cf. p. 152. 



Attention may also be drawn to the frequent arrangement of the cj^toplasm 

 in gland-cells in strands perpendicular to the free surface of the cell. It seems 

 probable that this structure is due to essentially similar conditions, the outer 

 or secreting surface ofthe plasma-membrane undergoing changes of permeability 

 and polarization, with the production of diffusion-potentials between the super- 

 ficial and the basal regions of the cell. , 



