THE BIOLOGY OF THE CELL SURFACE 



moves in and the yolk-spheres assume their original physical 

 appearance. These changes in the yolk-spheres show one 

 very delicate mechanism by which cells hold water. 



Fourth, the yolk-spheres are not alone concerned in the 

 water-holding capacity of the cell. The clear, apparently 

 structureless, cytoplasm and the nucleus have the power 

 of holding water and of losing it in the form of drops. 



It remains now to be decided how far we can apply these 

 conclusions on the findings on eggs under experimental 

 conditions to normal eggs in normal sea-water. Although 

 these eggs of the experiment were viable and capable of 

 recovery and complete development, they nevertheless 

 were subjected to an experimental treatment. 



However, these experiments of mine described above 

 were made with greatest care within limits definitely set; 

 the processes described can not be attributed to extensive 

 or drastic injury. There is thus less danger in making 

 statements concerning them as explanation for normal 

 conditions than in drawing conclusions concerning normal 

 processes from experimental procedures which killed the 

 eggs; the former only exaggerate, the latter extinguish the 

 process that we wish to explain. 



If the process of drop-formation of water observed in 

 these experimentally treated eggs is only an exaggeration 

 of a normal process, it should be possible, I thought, to 

 observe it both with other methods of treatment and in the 

 normal untreated Qgg. As a matter of fact, I have found 

 that the drops form as the result of pressure, of exposure 

 to ultra-violet light and after removing the eggs from normal 

 sea-water at 5°C. to that at room temperature (i9°C). 

 During exposure to hypertonic sea-water, the drops are 

 beautifully shown especially by fertilized eggs during every 

 stage of development and by cells in the young worm. In 

 unfertilized eggs in hypertonic sea-water the drops are 

 neither so numerous nor so easily visible. 



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