750 



SCIENCE 



[N. S. Vol. XXXVIII. No. 986 



a sufficient length of time such eggs are re- 

 moved from the sea water containing NaCN 

 to normal sea water they neither segment nor 

 disintegrate, and if sperm is added they will 

 develop into normal blastulae. If the eggs re- 

 main only 20 minutes in the alkaline solution 

 a very short exposure to the NaON solution 

 suffices. The longer the eggs remain in the 

 alkaline solution the longer they must also 

 remain in the cyanide solution if the effect of 

 the alkaline solution is to be reversed. If 

 they remain too long in the alkaline solution 

 a subsequent treatment of the eggs with NaCN 

 will only temporarily suppress the effects of 

 the alkali, but as soon as they are put back 

 into normal sea water they will disintegrate or 

 develop. In this case the effects of alkali 

 become irreversible. 



What has been said for the effects of the 

 alkali is also true for the effects of acid. If 

 we cause artificial membrane formation by 

 butyric acid in the eggs of Arbacia (without 

 submitting them to the second treatment) 

 they will begin to develop, but will disintegrate 

 very rapidly. If they are put after the mem- 

 brane formation for some hours into a cyanide 

 solution they will go back into a resting stage. 

 When transferred to sea water they will 

 neither segment nor disintegrate, and when 

 fertilized by sperm they will develop into 

 normal larvae. 



It is therefore obvious that the induction of 

 development in the egg of Arbacia by acid 

 or by alkali is a reversible process. 



The question arises : Which of the two 

 factors is reversible, the surface change (or 

 its effect in inducing development) or the 

 corrective factor, or both? The experiments 

 show plainly that the first factor is reversible. 

 In this respect the eggs of Arbacia differ 

 from those of Strong ylocentrotus. In the 

 latter the writer succeeded in suppressing tem- 

 porarily the disintegration following artificial 

 membrane formation by the suppression of 

 development with KCN, but the eggs when put 

 back into normal sea water either developed or 

 perished. There was no such reversion of the 



induction to development as we find in the 

 egg of Arbacia. This difference iu the be- 

 havior of both kinds of eggs is possibly con- 

 nected with a difference in the degree and pos- 

 sibly also the character of the alteration of 

 the cortical layer under the influence of 

 butyric acid. This is indicated externally by 

 the difference of the membrane to which the 

 writer had called attention in previous publi- 

 cations. While both types of alterations of the 

 cortical layer induce development, in the egg 

 of Arbacia this change is of a degree or char- 

 acter so as to be reversible, while in the egg of 

 Strongylocentrotus it is irreversible as far as 

 my present experience goes. When the eggs 

 of Arbacia are exposed too long to the alkaline 

 solution the change induced becomes also 

 irreversible. 



In the egg of Strongylocentrotus the correc- 

 tive factor is, as the writer has recently shown, 

 irreversible. When eggs, once treated with a 

 hypertonic solution which does not alter them 

 visibly and which leaves them intact, are at 

 any time after one or two days treated with 

 butyric acid, they will not disintegrate, but 

 develop in the same way as if the hypertonic 

 treatment had been applied after the mem- 

 brane formation. I have not yet tried whether 

 or not the same is true for the egg of Arbacia. 



It is impossible to state at present what the 

 nature of the reversible change is. The idea 

 has been expressed by E. Lillie that the induce- 

 ment of development (membrane formation) 

 consists in a rapid increase of permeability 

 and that the action of the hypertonic solution 

 is to restore a normal condition of permeabil- 

 ity in the egg.^ If this were the case, the 

 simultaneous application of the alkaline and 

 hypertonic solution should leave the egg 

 wholly or nearly intact, while in fact it is 

 just as effective as if we treat the egg first 

 with an alkaline solution and then with a 

 hypertonic solution. Moreover, the hyper- 

 tonic solution itself induces an alteration of 

 the surface of the egg (membrane formation) 

 which in the terms of this hypothesis would 



3 Lillie, Jour, of Morphol, XXII., 695, 1911. 



