RELATIVE SENSITIVENESS OF Fisu Emsryos' 315 
the dependence of processes of development upon the amount 
of water contained in the cells is therefore desirable. 
After some preliminary experiments with sea-water, whose 
concentration differed comparatively little from that of nor- 
mal sea-water, had shown that the Fundulus egg is most 
remarkably independent of the concentration of the sea- 
water, experiments were made with sea-water to which had 
been added 5, 7.5, 10, and 20 g. of NaCl to each 100 
c.c. of sea-water. Experiments were also made with nor- 
mal sea-water and fresh water as controls. Freshly fer- 
tilized eggs of Fundulus develop perfectly normally in 
fresh water as well as in sea-water to which 5g. of NaCl 
have been added to each 100 c.c. (that is, 50 g. per liter). 
When 7.5 g. of NaCl were added to each 100 c.c. of sea- 
water, a blastoderm was still formed; but only rarely an 
embryo, and if so the embryo had dwarf dimensions, and its 
development stopped before the optic vesicles were formed. 
In solutions to which 10 per cent. NaCl was added no embryo 
was formed. The segmentation of the eggs started in this 
case also, and occurred at first almost as rapidly as in normal 
sea-water, but it usually ceased at about the thirty-two-cell 
stage. I expected that these eggs would retain their power 
of development for some time after this, similarly to those 
kept in an oxygen vacuum. This was, however, not the case. 
Freshly fertilized eggs of Fundulus lost their power of devel- 
opment permanently after six to ten hours at a temperature 
of about 24° C. in sea-water to which 10 g. of NaCl had been 
added to each 100 c.c. When 20 g. of NaCl are added to 
each 100 c.c. of sea-water, the power of development of 
freshly fertilized eggs was annihilated in about three to four 
hours. The first segmentations, however, took place in such 
eggs. 
When Fundulus eggs are introduced into a 13.5 per cent. 
NaCl solution (or, more accurately, sea-water to which 10 g. 
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