316 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. 1 



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 

 do harm. [1903J 



