PHYSIOLOGY OF CELL-DIVISION 397 



trial mitoses; they appear also to exert a direct influence on 

 surface-tension, in the manner indicated below. Hence they 

 undoubtedly form important accessory factors in cytoplasmic 

 division, in addition to the primary factor of altered surface- 

 polarization already considered. 



This view regards asters (radiating areas in the cytoplasm) , 

 as temporary formations due to local chemical change, and 

 hence accords with conceptions widely held among cytologists. 

 Wilson describes "the rapid and complete disappearance of 

 the rays upon cooling or etherization and their reappearance 

 upon recovery;" this is inteUigible, he says, ''if the aster be 

 only a radial configuration of the alveolar meshwork caused 

 by an activity in the cytoplasm that is diminished or suspended 

 by lowered temperature or etherization and renewed upon 

 recovery."^'- Other cytologists express similar views. F. R. 

 Lilhe finds that when basophile particles, normally not present 

 in the substance of the astral radiations, are artificially driven 

 by centrifugalization into the spindle-area, they assume regular 

 orientation along the strands and contribute to the formation 

 of spindle and astral fibers.^^ "The center of force hypothesis 

 offers the only consistent explanation of such behavior." These 

 facts are plainly in harmony with the general conception that 

 the centrosomes represent local accumulations of a special sub- 

 stance, 'archiplasm,' which influences the configuration of the 

 cytoplasm only when it undergoes chemical change. ^^ It seems 

 also necessary to regard this substance as a product of cell- 

 metabolism and colloidal in character; such a view explains 

 the possibility of its continued production, and certain features 

 of its behavior — e.g., the multiphcation of centrosomes by divi- 

 sion, the formation of supernumerary asters, the transport of 

 kinetoplasm from cell to cell (as seen in the formation of sperm- 

 asters in fertilization), and similar phenomena. It has been 

 suggested above that the chemical change which it undergoes 



52 Loc. cit., pp. 384, 38.5. 



^■^ F. R. Lillie, Biological Bulletin, 1909, vol. 17, p. 101. 



»•* This corresponds to Conklin's above-quoted conception of asters as repre- 

 senting isolated portions of archiplasm which assume the aster form during 

 mitosis. 'Cytasters appear to be physiologically similar to cleavage asters, and 

 to result from alteration of the same material. 



