ARTIFICIAL PRODUCTION OF NORMAL LARVJE 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 Hydromedusse 

 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 -|w 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. *n 



