138 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
In order to make the above discrepancies comprehensible, 
we must remember how many variations of constitution come 
into play in this experiment. We saw first that the effect of 
the acid increases with the number of carbon atoms, secondly 
that the entry of an HO-group has the opposite effect, and 
thirdly that the ‘“linear”’ coupling of the carbon atoms is more 
effective than the “branched” (oxybutyrie and oxyisobutyric 
acids). All these and other conditions of constitution prob- 
ably come under consideration in the explanation of this appar- 
ently irregular acid effect of the last table. The number of 
acids investigated is not sufficient for a detailed analysis. 
It is even truer of the mineral than of the dibasic organic 
acids that they are able to cause membrane formation only in 
the eggs of some, but not all females. With sulphuric acid in 
particular I have never yet been able to evoke membrane 
formation in the sea-urchin egg;! I have done so occasionally 
with HNO, and HCl, but not always. The most favorable 
results that I have obtained with these two acids are summed 
up in Table XXIII. 
TABLE XXIII 
Length of Exposure to— | N/500 HCI|N/500HNO,| %{500N | 3/500N 
jsminuterts emereenee 0 0 | 5% 90% 
PUMA GeSracreere seat Oe 0 LO = | 90 Seat, 
Seminutesacne sees 70% 80 100 
ASTMINUPES a rel neice 10 90 1060 
HyMINUtesae cease 20 1003 Stee 
Gominutesesae eee 305 Oe ae ees 
(ominutese pee eee SOl sil, ae are eee 
Siminutesmeer ie ea renee SOM sacl tus Siete ay 2 eee 
Oimiinutestese: cache SOSS= > Mil siSrse cen | eee 
1OMMIMUES ae eee OOF a ake ee eens 
Usually, however, the results are more of the kind given 
for comparison in Table XXIV. 
1Tt seems to be a general experience that sulphates diffuse less easily into 
living cells than chlorides. 
