254 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



Delage 1 found that the ripe eggs of Asterias glacialis 

 developed into larvae if he used carbonic acid in the place of 

 the acids employed by us. He put the eggs after maturation 

 in sea-water saturated with carbonic acid for five to fortv-five 



*.' 



minutes. As shown by the experiments of Godlewski and 

 myself, carbonic acid is one of the acids suitable for membrane 

 formation; it diffuses easily into the egg and there brings about 

 those changes which underlie membrane formation. The greater 

 efficiency of CO 2 is due to the fact that it is a very weak 

 acid and hence diffuses easily into the egg. 



This idea is supported by Delage's observation that the 

 number of Asterias eggs that develop after the carbonic-acid 

 treatment is further increased if the oxygen is removed for 

 some time from the solution (Delage, 1907), though he does 

 not state why this should be so. We can understand this fact 

 from the observation which the writer made on the egg of the 

 sea-urchin that, after membrane formation, lack of oxygen 

 gives the egg an opportunity to recover from the threatening dis- 

 integration. The same thing occurs in the starfish egg; and 

 we can understand why more eggs of the starfish develop if 

 they are kept without oxygen during and for some time after 

 the exposure to C0 2 , than if they are all the time in contact 

 with oxygen. The reason for this is to be found in the fact 

 that treatment with C0 2 causes the development by calling forth 

 the change in the cortical layer of the egg. If the eggs begin 

 to develop under these conditions, a few reach the larval stage, 

 while many disintegrate; but if the development is retarded 

 for a while, all the eggs have a chance to recover from the 

 threatening disintegration or to produce the substance which 

 saves them from the threatening disintegration. Unfortunately 

 Delage has overlooked my experiments upon the beneficial effect 



1 Yves Delage, "Nouvelles recherches de la parthenogenese experiment ale 

 chez Asterias glacialis," Arch, de Zool. exper. et gen., 3. S., X, 213, 1902; " Elevage 

 des larves parthenogenetiques d' Asterias glacialis," ibid., 4. S., II, 27, 1904; 

 " Xouvelles experiences de parthenogenese experimentale," ibid., 4. S., Ill, CLXIVt 

 1905; Compt. rend. Acad. Sc. CXLV, 218, 1907. 



