488 DEVELOPMENT 



adsorbed electrolytes are set free, so increasing the electrical 

 conductivity of the cell. Whatever be the actual physico-chemical 

 process brought about by the entrance of the spermatozoon, the 

 result has been imitated by simple physico-chemical means. 



If, after removal from the butyric acid bath (or other cytolytic 

 agency), the egg is placed in hypertonic sea-water for about half 

 an hour and then returned to its normal environment it will, 

 in all likelihood, reach maturity. That is, not only does artificial 

 membrane formation initiate the processes of development, but it 

 starts, at the same time, processes zvhich ultimately lead to the dis- 

 solution of the organism. 



These latter activities may be, for a time, suspended, by a short 

 exposure to a hypertonic solution. 



Loeb has proved that the withdrawal of water is merely the 

 trigger setting off a series of chemical as well as physical changes. 

 Attention has been repeatedly drawn in previous pages to the fact 

 that while most physical processes have a low, or even a negative 

 temperature coefficient, most chemical reactions have a high 

 (^10 = - or more) temperature coefficient. This worker found 

 that, at a temperature of 5° C, the eggs had to remain in the 

 hypertonic solution for at least 210 minutes. The time of ex- 

 posure was decreased to 40 minutes when the temperature of the 

 solution was raised to 15°. Therefore, the temperature coefficient 

 for this process is 



210 . 



Hence, superimposed on the physical process of exosmosis are 

 secondary chemical reactions initiated by it. 



Spermatozoon. Attempts have been made to determine what 

 part the spermatozoon plays in the process of fertilisation, 

 Brailsford Robertson has extracted a substance, oocytin, fVom the 

 testicles of the sea-urchin which produces membrane formation. 

 The question then arises — " Is this substance a catalyst speeding 

 up some slow change or docs it counteract some obstacle to 

 development ? " To the first jjart of the question a negative 

 answer can be given. The velocity of the process of development 

 is not catalytic. It docs not follow Schiitz's law and vary in 

 velocity with the square root of the concentration. If two 

 spermatozoa are caused to enter an ovimi, the rate of segmentation 

 should increase by 1-4 {i.e. V2) times, if the process were catalytic. 

 The rate, as a matter of fact, is unaltered by the introduction of 

 additional spermatozoa. Therefore, the spermatozoon does not 

 contain a catalyst for developmental processes. 



