220 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
formation if eggs lie for some time in sea-water? No definite 
answer can be given.. The effect may possibly be due to the 
action of the NaOH contained in the sea-water. 
2. In his experiments on inducing development by foreign 
blood, the writer made the following observation. The unferti- 
lized eggs of a sea-urchin were placed in a mixture of 1 c.e. 
WWE 
Fics. 66-72.—Camera drawings of unfertilized eggs of S. purpuratus which 
had begun to segment spontaneously. In all the eggs a fine gelatinous membrane 
was formed. 
of pig’s serum and 1 ¢.c. of SrCl, isotonic with sea-water. After 
five minutes this solution was pipetted off and replaced with 
sea-water, which process was repeated four times. The eggs 
were left in the watch glasses for four hours and then trans- 
ferred to a larger bowl of sea-water. Only a small number of 
the eggs had formed membranes, and these perished after a 
little while in the early segmentation stages. But a few of the 
other eggs, which had apparently not formed membranes, began 
to divide and they developed into normal swimming larvae, 
perishing in the blastula stage. Similar results were obtained 
