RELATIVE SENSITIVENESS OF FISH EMBRYOS 317 



mat ion of the blastoderm. Some eggs were introduced into 

 the 13.5 per cent, solution one hour after fertili/ation; after 

 five hours' cleavage had gone on in these eggs to about the 

 thirty-two-cell stage. Half of these eggs were then returned 

 to normal sea-water, while the remainder were left in the 

 concentrated solutions. Three hours later the latter had lost 

 their power of development, with the exception of three 

 among hundreds of specimens. The other portion of the 

 eggs, after having remained for eighteen hours in normal sea- 

 water, were returned again to the 13.5 per cent. NaCl solu- 

 tion. A large percentage of these eggs formed embryos 

 which remained alive in this concentrated solution for more 

 than a week. 



A remarkable phenomenon was observed in the embryos 

 which developed in the very concentrated solutions; namely, 

 that the maximum concentration of the sea- water in which the 

 embryo is able to develop completely is much higher than the 

 maximum of the solution in which the fully developed embryo 

 is able to hatch from the <</(/. When normal Fundulus em- 

 bryos are introduced in the second week of their development, 

 into sea-water to which 10 per cent. NaCl was added they con- 

 tinue their development, but they do not hatch, but die 

 within the egg. This phenomenon shows itself still more defi- 

 nitely when more dilute solutions are used. If 5 g. of NaCl 

 are added to 100 c.c. of sea-water, the embryos develop in a 

 normal way in this solution, and remain alive for more than 

 five weeks without hatching. If, however, the eggs are intro- 

 duced into normal sea-water as soon as the embryo is fully 

 developed (after about two or three weeks), the embryo 

 hatches in one or two days. This fact may be connected in 

 some way with the fact that the fish which has just hatched 

 is more sensitive to the concentrated sea-water than the two- 

 day-old embryo. The former dies in a 13.5 per cent. NaCl 

 solution in less than twenty-four hours. It can live, how- 



