398 RALPH S. LILLIE 



at kinesis is an oxidation, resulting in the formation of acid 

 products; this view agrees with the fact that cell-division is 

 prevented by cyanide or lack of oxygen, and that polar and 

 other radiations once formed are suppressed by cold, etheriza- 

 tion, or exposure to boiled sea-water or a hydrogen atmosphere." 

 Mathews has put forward the hypothesis that the reason why 

 aster-formation and cell-division are not possible in eggs until 

 the germinal vesicle has broken down, is due to the necessity 

 of some nuclear component, e.g., oxidase, for the oxidation- 

 process in question. The cytological evidence that the centro- 

 somal substance is of nuclear origin, or at least has a nuclear 

 component, is very strong. '^^^ 



The relation of astral formations to cytoplasmic division may 

 now be briefly considered. These structures have long been 

 regarded as especially concerned in the change of form of dividing 

 cells; as "an expression of the forces operative in the division 

 of the cell-body" (Wilson)," or as influencing the surface-tension 

 of the cell (Conklin).^^ Enucleate cells containing asters may 

 divide or undergo changes of form;^^ this happens especially 

 when the asters approach the cell-surface; the region adjoining 

 such an aster shows increased curvature, indicating increased 

 surface-tension; cleavage furrows, and in some cases complete 

 separation of portions of protoplasm, may result. The in- 

 fluence of astral areas in causing changes of form is most clearly 

 seen in enucleate eggs, or in eggs containing supernumerary 

 asters, or in which the conditions of the asters is artificially 

 modified, e.g., by etherization; single asters may give rise to 

 cleavage-furrows; their activity is greatest when they are near- 



*^ Numerous instances of these effects are described in the already quoted 

 papers of Wilson and Conklin. For the relation of oxygen to astral radiations 

 cf. especially Mathews: loc. cit., p. 98. 



" Cf. Mathews, Amer. Journ. Physiol., 1907,. vol. 18, p. 94. The dissolution 

 of the nuclear membrane is probable one of the changes resulting from the initial 

 surface-depolarization of the cell, as suggested in my paper in the Journal of 

 Morphology, loc. cit., p. 727; centriole-forming- material would then be free to 

 enter the cytoplasm. 



"Loc. cit., p. 380. 



s»Loc. cit., p. 532. 



"Cf. Wilson, Arch. f. Entwicklungsmech., 1901, vol. 12, p. 551; McClendon, 

 ibid., 1908, vol. 26, p. 662. 



