794 BIOPHYSICAL PHENOMENA [pt. iii 



egg will stand. Ramult has found, however, that Salmo trutta eggs 

 are more resistant than other varieties, a fact probably connected 

 with the adult habits of the fish which inhabits fresh and salt water 

 indiscriminately. 



The osmotic pressure of the contents of the teleost egg, therefore, 

 is constant throughout development, and so differs profoundly from 

 that of the amphibian zgg. Runnstrom noticed that the membranes 

 of oviduct eggs were very fragile and easily broken, whereas im- 

 mediately after laying they were hard and tough. Comparative 

 centrifugation and experiments on solubiHty in 3 per cent, potassium 

 hydroxide easily demonstrate this. In 10 per cent, salt solution 

 the hardening does not take place. Obviously these changes in the 

 egg-membranes are of great importance with respect to the osmotic 

 behaviour of the teleost egg, and perhaps may be regarded as the 

 causes of its special properties. Runnstrom concluded that another 

 function of the membrane was protection against polyspermy. He 

 also made experiments with potassium chloride solutions, finding the 

 time taken for the salt to diffuse through the membranes and stop 

 the heart-beat. In this way he observed that the egg-membranes 

 were much less permeable than the skin of the hatched larvae, just 

 as Loeb had previously done for Fundulus embryos. For further details 

 see the section on Susceptibility and Resistance. 



In considering the difference between the behaviour of teleosts 

 and amphibia as regards osmotic pressure, it must be remembered 

 that during development up to hatching, and for a short time after- 

 wards, the water-content of both amphibian and teleost embryos (or 

 rather embryo plus yolk) is steadily increasing. Yet amphibian eggs 

 will not develop properly in solutions isotonic with the adult tissues, 

 while those of teleosts will. 



Further details are afforded us through the researches of Bogucki, 

 who set up the egg-membranes in microdialysers and studied the 

 passage of substances through them. In this way he found that they 

 were penetrable by chlorides, monosaccharides and amino-acids, but 

 not by proteins, polysaccharides or colloids such as Congo red. 

 During development the permeability was not modified: the same 

 amount of potassium chloride dialysing through in a given time at 

 10 or 30 days from fertilisation. The initial intake of water after 

 fertilisation was correlated by Bogucki with the formation of the 

 perivitelHne liquid, which just accounts for the change. Bogucki 



