Errect or [ons upon TIssvug 575 
stages of the development of the Fundulus egg occur in a 
normal way. The fact that such a solution does not contain 
any Na ions raises the question whether the main importance 
of ions in these phenomena does not lie in the influence they 
have upon the physical qualities of the protoplasm (absorp- 
tion of liquids, state of matter, etc.) If this were the case, 
we might easily understand that various mixtures of ions 
might bring about the same effect upon tissues, provided 
that they affect the physical qualities of the protoplasm in 
the same manner. In the next paper we shall show that the 
eggs of the sea-urchin can reach the blastula stage in a 
mixture of 129n MgCl, andi CaCl,. But each of these 
vicarious mixtures serves only for a certain class of vital 
processes, while a mixture of NaCl with a small amount of 
Ca and K ions allows the whole cycle of life phenomena 
(with certain exceptions) to be completed. 
5. Herbst’ has tried to prove that practically every sub- 
stance contained in the sea-water is necessary for the devel- 
opment of the egg of the sea-urchin. His proof consisted 
chiefly in removing one of the constituents of the sea-water, 
and showing that in such modified sea-water the eggs were 
not able to develop. This method does not warrant the con- 
clusions Herbst has drawn from them. In a solution of 96 
c.c. 5n NaCl + 2 c.c. 4% CaCl, + 2 ¢.c. §n KCl all the Fun- 
dulus eggs develop and hatch. If we remove the Ca ions, 
the majority of Fundulus eggs cannot develop, and of the 
few that develop none hatch. According to Herbst it would 
follow that the surrounding medium must contain Ca ions 
for the development and hatching of the Fundulus eggs. 
Yet we have seen that the Fundulus egg develops and 
hatches in distilled water. Ca ions become a necessity only 
if the surrounding solution contains Na ions in excessive 
quantities. 
1HeErsst, Archiv fir Entwickelungsmechanik, Vol. V (1897), p. 649. 
Digitized by Microsoft® 
