596 STUDIES IN GENERAL PHYSIOLOGY 
existence of a membrane may serve to show whether eggs 
were fertilized or not. The fertilized eggs that were put 
into the second solution (KCl) did not reach the blastula 
stage. They stopped at about the thirty-two- to the sixty- 
four-cell stage. Those that had been in the third solution 
(NaCl) were in about the same condition, with the exception 
perhaps that at first the segmentation was more unequal. 
In the fourth solution (CaCl,) no egg segmented, and only 
one egg in a thousand showed a beginning of segmentation, 
consisting of an incision at one side of the egg. 
I finally wished to know how fertilized and unfertilized 
eggs behaved if left for eighteen hours in a mixture of 
60 cc. 2Pn MgCl, +40 c.c. sea-water. The unfertilized 
eggs formed no membrane, but a very large part, more 
than 50 per cent., of the eggs was divided into from 2 to 8 
cells. The fertilized eggs had a membrane. In regard to 
segmentation there was little difference between the two lots. 
It was especially this circumstance which made me hope 
that with a little more care it would be possible to raise liv- 
ing larve from unfertilized eggs by treating them with a 
suitable mixture of *,2n MgCl, solution and sea-water. 
In these and other similar experiments, which I will not 
describe, it was moreover evident that after the treatment 
with Mg ions the character of the segmentation was much 
more normal than after the treatment with K and Na or Ca 
ions. The K ions were nearest the Mg ions in their effect. 
TheCaions were the most unfavorable. Theformerexperiments 
of Norman had also yielded the result that the Mg ions were 
the most harmless for the segmentation of the sea-urchin egg. 
IV. THE ARTIFICIAL PRODUCTION OF NORMAL LARV& (PLU- 
TEI) FROM THE UNFERTILIZED EGG OF THE SEA-URCHIN 
The most serious danger in experiments with unfertilized 
eggs is the possibility that the sea-water or the instruments 
Digitized by Microsoft® 
