ARTIFICIAL PRODUCTION OF NORMAL LARVAE 615 



(1) 50c.c. *n MgCl 2 +50c.c. sea-water 



(2) Normal sea-water 



Two hours later the eggs from solution 1 were put back 

 into normal sea-water. Three and a half hours later about 

 50 per cent, of the eggs that had been in solution 1 were 

 divided into from 2 to 16 cells, but not an egg had a mem- 

 brane. The control eggs that had been in normal sea-water 

 all the time were all without membrane and absolutely unseg- 

 mented. Millions of eggs were examined under the micro- 

 scope. The next morning the eggs that had been in solution 

 1 had reached the blastula stage and were swimming about. 

 A small number were in a gastrula stage and even beginning 

 to assume a pyramidal form. In the control eggs not one 

 had developed. Perhaps one in a hundred had amoeboid 

 forms such as precede segmentation in unfertilized eggs, but 

 not an egg was segmented, and not one had a membrane. 

 The next day some of the blastulse of the other lot had 

 reached the pluteus stage. The control experiments will be 

 discussed in the next paragraph. 



Possible sources of error and objections. From all these 

 experiments I draw the conclusion that by putting the unfer- 

 tilized eggs of Arbacia for two hours into a solution of 60 c.c. 

 ^ n MgCl 2 -j- 40 c.c. sea- water the eggs develop into blastulse 

 if brought back into normal sea- water. If we put the unfer- 

 tilized eggs for about two hours into a solution of equal parts 

 of 2 n MgCl 2 and sea-water, the eggs may reach the pluteus 

 stage. The possible objection might be that the eggs were 

 fertilized. Such fertilization could only have been caused 

 by the instruments or hands of the experimenter having 

 been in contact with spermatozoa, or by the sea-water con- 

 taining spermatozoa. The first possibility was absolutely 

 excluded through the above mentioned precautions. The 

 second possibility was rendered practically impossible, as, 

 first, the spawning season was practically over, and, second, 



