816 STUDIES IN GENERAL PHYSIOLOGY 
of NaCl have been added to each 100 c.c.), twenty-four 
hours after fertilization (before the beginning of the forma- 
tion of the embryo) not only an embryo is formed in these 
eggs, but the embryo develops every individual organ; the 
heart-beats and the circulation are established, and the 
embryo shows motions after several days. It lives in this 
concentrated salt solution for ten to fourteen days. Only in 
three points did the development of such embryos differ 
from that in normal sea-water: the embryos grew much more 
slowly in the concentrated sea-water than in normal sea- 
water; secondly, the development of the individual organs 
was somewhat delayed; and, finally, the yolk shrunk much 
more rapidly than under normal conditions. 
Only a relatively small percentage of the eggs which were 
introduced into concentrated sea-water twenty-four hours 
after fertilization were able to develop. When eggs were 
introduced, however, into the 13.5 per cent. solution forty- 
eight hours after fertilization, a larger percentage developed. 
After the third or fourth day the eggs could be transferred 
from normal sea-water directly into a 27.5 per cent. NaCl 
solution without interrupting development! Development 
continued for about three or four days. The circulation was 
not interrupted, even though the beat of the heart had 
become somewhat slower. The velocity of development and 
growth was the less the higher the concentration.’ 
We see, therefore, that the sensitiveness to loss of water 
is incomparably greater during the early period of segmenta- 
tion of the Fundulus embryo than later, and that even then 
the sensitiveness decreases somewhat with progressive devel- 
opment. The following experiment is suited to show the 
great difference in the sensitiveness before and after the for- 
1 These experiments may perhaps find their explanation on the assumption that 
after twenty-four hours the permeability of the egg or the germ-cells is diminished, 
and hence the NaCl cannot longer enter fast enough in sufficient concentration to 
doharm. (1903] 
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