254 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
Delage’ 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 forty-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, 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 CO,, 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 CO, 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 parthénogénése expérimentale 
chez Asterias glacialis,’’ Arch. de Zool. expér. et gén., 3. 8., X, 213, 1902; “ Plevage 
des larves parthénogénétiques d’Asterias glacialis,”’ ibid., 4. S., II, 27, 1904; 
‘“ Nouvelles expériences de parthénogénése expérimentale,” ibid., 4.S., III, CLXIV> 
1905; Compt. rend. Acad. Sc. CXLV, 218, 1907. 
