318 STUDIES IN GENERAL PHYSIOLOGY 



ever, in a 6.5 per cent, solution. In fresh water the embryos 

 hatch just as rapidly as in normal sea-water. The fish is 

 able to live in fresh water. 



I know of no other animal which is able to stand such 

 great and sudden variations in the concentration of the sea- 

 water as the Fundulus embryo. The question might arise 

 whether this depends upon a peculiar characteristic of the 

 egg membrane or the protoplasm. It can be shown that the 

 protoplasm is relatively insensitive to variations in concen- 

 tration, while diffusion through the egg membrane occurs 

 very promptly. In order to prove the latter I have to call 

 attention to my earlier experiments on the action of KC1 

 upon the Fundulus embryo. 1 The addition of 3 g. of KC1 

 to 100 c.c. of sea-water brought the heart of one of the older 

 Fundulus embryos to a standstill in a minute. A consider- 

 able amount of this salt must, therefore, diffuse through the 

 egg membrane in a very short time. That the protoplasm is 

 very insensitive to variations in concentration can be shown 

 on the spermatozoa. I convinced myself, first of all, of the 

 fact that the unfertilized Fundulus egg can form neither an 

 embryo nor segment. I then introduced eggs, under bac- 

 teriological precautions, into sea-water to which 5 g. of NaCl 

 had been added to 100 c.c. When I added spermatozoa to 

 so concentrated a solution, the eggs developed as in normal 

 sea- water. The movements and the power of fertilization of 

 the spermatozoa must, therefore, be retained in such a solu- 

 tion. The spermatozoa also retain their power of fertiliza- 

 tion in fresh water. I believe also that they still penetrated 

 the egg in a 13.5 per cent, solution. I neglected, however, 

 to follow this experiment more accurately, and so must leave 

 this fact undecided for the time being. The fact that the 

 spermatozoon retains its functions in an 8.5 per cent. NaCl 

 solution is sufficient, however, to show that the independence 



1 Part I, pp. 297, 298. 



