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.c. 



FIGS. 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.c. of SrCl 2 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 



