[40 A. P. MATHEWS. 



eggs in every lot formed swimming embryos when restored to 

 sea-water. 



While the results were thus not sharp and decisive, as in Ar- 

 bacia, and the resistance of the egg to the cyanide very much 

 greater, the experiments were generally harmonious in showing 

 more abnormal embryos in the period just preceding segmen- 

 tation. In the one exception there were no clear differences 

 between the eggs introduced into the cyanide at different periods. 



Why the Arbacia eggs are more susceptible when the asters 

 are developing is of course entirely obscure. At this period it is 

 probable, from unpublished observations, that an oxidase escapes 

 from the nucleus and exerts its action upon the cytoplasm. It is 

 possible, also, that at this period the reducing substance in the 

 centriole becomes more active. By an increase in activity is 

 meant an increase in combining power. It may be, therefore, 

 either that the cyanide prevents the oxidase from exerting a nec- 

 essary action, or it combines with the active centriole and de- 

 stroys its action, whereas it does not combine with the inactive 

 centriole substance. Further investigation is necessary to decide 

 whether either of these suggestions is the correct explanation. 

 The great resistance of the eggs of Astenas Forbcsii to the cy- 

 anide cannot be explained without further experiment. 



