RELATIVE SENSITIVENESS OF FISH EMBRYOS 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 5 g. 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. 



