ARTIFICIAL PRropucTion oF NormMaL Larva 541 
to the formation of a blastula. A heap of cells, at the best 
about sixty, were formed, and then everything stopped. 
We cannot utilize these observations for the theory of 
fertilization, for the simple reason that the essential element 
of the process of fertilization, namely, the formation of an 
embryo, was lacking. In the case of tumors or galls we have 
cell-division and even growth, and yet these cell-divisions do 
not result in the formation of an embryo. 
3. Some recent observations suggested to me that some- 
thing in the constitution of the sea-water prevented the 
unfertilized eggs of marine animals from developing parthen- 
ogenetically. Last year I found that the striped muscles 
of a frog beat rhythmically (like the heart) if put into a} 
NaCl or NaBr solution. It is only the presence of K and 
Ca ions in the blood that prevents striated muscles from con- 
tracting rhythmically in the body. Romanes had observed 
that if the margin (with the nerve ring) in Hydromedusee 
be cut off, the center no longer contracts rhythmically. I 
found this summer that this is due solely to the presence of 
K and Ca ions in the sea-water. In a 4n solution of NaCl, 
or still better of NaBr, the center continues to beat spon- 
taneously. In applying this and my more recent observa- 
tions on the relative influence of the various ions upon seg- 
mentation to the problem of artificial parthenogenesis it 
seemed to me that by making two changes in the constitu- 
tion of sea-water the eggs of the sea-urchin might be able to 
produce perfect embryos without being fertilized. These 
changes were either a reduction of the Na and Ca ions or an 
increase in the Mg (or K) ions or both. I think that a great 
number of variations in this sense might bring about the 
desired effect, but the end of the season allowed me to try 
only a limited number of variations. Without going into 
details (which may be reserved for the full report) I will 
state briefly that the mixture of about 50 per cent. 4n 
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