278 BIOLOGICAL LECTURES. 



ions contained in the muscles of the skeleton we can make 

 them contract rhythmically like the heart. It is only necessary 

 to increase the number of sodium ions in the muscle or to reduce 

 the number of calcium ions or both simultaneously.^ On the 

 basis of this and similar observations I thought that by chang- 

 ing the constitution of the sea water it might be possible to 

 cause the eggs not only to show a beginning of development 

 but to develop into living larvae, which were in every way 

 similar to those produced by the fertilized Q.g^. 



There seemed to be three ways in which this might be 

 accomplished. The first way was a simple change in the con- 

 stitution of the sea water without increasing its osmotic pres- 

 sure. The second way was to increase the osmotic pressure 

 of the sea water by adding a certain amount of a certain salt. 

 The third way was by combining both of these methods. The 

 first way did not lead to the result I desired. All the various 

 artificial solutions I prepared had only the one effect of causing 

 the unfertilized Qgg to divide into a few cells, but I was not 

 able to produce a blastula. I next tried the effects of an 

 increase in the sea water by adding a certain amount of mag- 

 nesium-chloride. In this case I had no better results than 

 Morgan. Very few eggs began to divide, but these did not 

 develop beyond the first stages of segmentation. I then tried 

 the combination of both methods. The osmotic pressure of 

 ordinary sea water is roughly estimated to be the same as that 

 of a I nNaCl solution or a 3J^ nMgCU solution. I found, after 

 a number of experiments, that by putting the unfertilized eggs 

 of the sea urchin into a solution of 60 c.c. of -^gO- nMgCl2 solu- 

 tion and 40 c.c. of sea water for two hours the eggs began to 

 develop when put back into normal sea water. Such eggs 

 reached the blastula stage. I do not think that anybody has 

 ever seen before such blastulae as resulted from these unferti- 

 lized eggs. As these eggs had no membrane, the amoeboid 

 motions of the cleavage cells led very frequently to a discon- 

 nection of the various parts of one and the same Q.g^, and the 

 outlines of the tg^ became extremely irregular. The blastula 



1 It is due to the Ca ions of our blood that the muscles of our skeleton do not 

 beat rhythmically like our heart. 



