474 THEOPHILUS S. PAINTEK 



cytoplasmic radiations. There is, in short no aster — though 

 centrosomes may be present — and yet there is a flow of proto- 

 plasm into the cleavage plane and the eggs divide. 



FURTHER DISCUSSION 



As striking as these experiments with phenyl urethane may 

 appear at first, the results were not wholly unexpected in 

 the light of other researches. Wilson ('01 b) observed that 

 when he allowed the ether to evaporate in the dishes where 

 eggs were, that eventually these eggs would attempt an abor- 

 tive sort of division. 6 During this time the asters were but 

 feebly developed. And Teichmann ('03), repeating Wilson's 

 experiments on Echinus microtuberculatus, remarks that he 

 observed an egg divide after being treated with ether, in which 

 he could observe no astral radiations. Neither of these authors 

 gave the matter any closer study. 



In Arbacia we have as typical a development of the aster as. 

 is to be found among animal cells, and yet the experiments with 

 phenyl urethane show that in the total absence of these strik- 

 ing structures, the egg may undergo cleavage. Whatever the 

 function of the aster may be, these experiments make it clear 

 that a second factor (or set of factors) is at work which operates 

 to bring about cytoplasmic cleavage. This division is accom- 

 panied by a swelling of the ectoplasmic layer and a flow of 

 pigment towards the cleavage furrows. 



To return to the question of the cause of protoplasmic move- 

 ment, it is clearly demonstrated that neither the aster nor the 

 processes involved in its formation (centripetal flow of ground 

 substances, Rhumbler ('96), etc.) are responsible for the swel- 

 ling of the hyaline layer or for the flow of pigment granules into 

 the cleavage furrow or for the cleavage itself. This forms very 



6 Warburg ('11) has shown that dilute solutions of phenyl urethane, such as 

 I have used, do not materially alter the rate of oxidation of sea urchin eggs. 

 Ether, however, (and a number of other narcotics) does diminish the oxidation 

 rate. It is possible that the greater activity which the eggs of my experiment 

 showed was due to this difference. 



