Nature of the Process of Fertilization 119 



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 egg 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 f n NaCl solution or a ^-n MgCl.^ solution. I found, after 

 a number of experiments, that by putting the unfertiHzed eggs 

 of the sea-urchin into a solution of 60 c.c. of -^^-n MgClg 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 egg, and the 

 outlines of the egg became extremely irregular. The blastulae 

 showed, as a rule, the same outline as the egg had in the morula 

 stage. It was, moreover, a rare thing that the whole mass of 

 the egg developed into one blastula. The disconnection of the 

 various cleavage-cells led, as a rule, to the formation of more 

 than one embryo from one egg. The results were in a certain 

 way similar to those I had obtained when I caused the fertilized 

 eggs of sea-urchins to burst. In such cases a part of the proto- 

 plasm flowed out from the egg but was able to develop. These 

 extraovates had no membrane, and of course showed some 

 irregularity in their outlines, but the irregularity in this case 



1 Later experiments gave, however, positive results. See next chapter. 



