Nature of the Process of Fertilization 117 



• 



into two, four, eight, sixteen cells, etc. Of course it is neces- 

 sary for this experiment that the right increase in the concen- 

 tration of the sea-water be selected. The explanation of this 

 fact is as follows: The concentrated sea-water brings about 

 a change in the condition of the nucleus which permits a division 

 and a scattering of the chromosomes in the egg.^ As soon as 

 the egg is put back into normal sea-water it at once breaks up 

 into as many cleavage-cells as nuclei or distinct chromatin 

 masses had been preformed in the egg. Morgan tried the same 

 experiment on the unfertilized eggs of the sea-urchin, and 

 found that the unfertilized egg, if treated for several hours with 

 concentrated sea-water, was able to show the beginning of a 

 segmentation when put back into normal sea-water. A small 

 number of eggs divided into two or four cells, and, in a few 

 cases, went as far as about sixty cells, but no larvae ever devel- 

 oped from these eggs. Morgan^ had used the same concen- 

 tration of sea-water as Norman^ and I had used in our previous 

 experiments. I had added about 2 grams of sodium chloride 

 to 100 c.c. of sea-water. Norman used instead of this 3J grams 

 of MgCl2 to 100 c.c. of sea-water, and Morgan used the same 

 concentration. Mead'^ made an observation somewhat similar 

 to Morgan's upon Chaetopterus. He found that by adding a 

 very small amount of KCl to sea-water he could force the unfer- 

 tilized eggs of Chaetopterus to throw out their polar bodies. 

 The substitution of a little NaCl for KCl did not have the 

 same effect. While continuing my studies on the effects of 

 salts upon life phenomena, I was led to the fact that the peculiar 

 actions of protoplasm are influenced to a great extent by the 

 ions contained in the solutions which surround the cells. As is 



1 Loeb, J., "Experiments on Cleavage," Journ. of Morph., VII, 1892. 



2 Morgan, T. H., "The Action of Salt Solutions, etc.," Arch. f. Eutwickelungs- 

 mechanik, VIII, 1899. 



3 Norman, W. W., " Segmentation of the Nucleus without Segmentation of the 

 Protoplasm," Arch. f. Entwickelungsmechanik, III, 1890. 



^ Mead, A., "The Rate of Cell-Division and the Function of the Centrosome," 

 Woods Hole Biol. Led., 1898. 



