^10 E. G. Spaulding 



Substituting, we get 



p = .0063 atmos. 



Although, therefore, it appears from this that there has been an 

 increase in the pressure which would result from the curved sur- 

 face of the egg were this a film, it is also evident that this is of 

 insignificant value in comparison with the values, 7.32, 6.53, 6.40 

 atmos. found for the inhibiting solutions. It falls "outside the 

 limits of error," and is, therefore, to be neglected in the applica- 

 tion of the "work integral." 



The fact, however, that this pressure has such a small compara- 

 tive value, results, evidently, from the substitution of .01 as the 

 coefficient of surface tension of protoplasm. The acceptance of 

 this value is, of course, purely gratuitous; but if it be approxi- 

 mately correct for the protoplasm of the sea-urchin egg, then the 

 resulting small value of the pressure of the surface on the basis of 

 the assumption that this is a film proves this assumption to be 

 incorrect, and indicates that there must be a membrane, differ- 

 entiated from the cytoplasm, to oppose the relatively high internal 

 pressure as indicated by the strength of the solutions requisite to 

 inhibit segmentation. 



There has been demonstrated, then, experimentally, an increase 

 of 7.32 atmos. in the "resultant" pressure, as brought about by 

 fertilization and the process following it up to the time of segmen- 

 tation. As a result of these, the egg normally cleaves; it changes 

 form, and it is now shown experimentally that as it does this 

 the internal pressure therewith decreases; without fertilization 

 these events do not take place. 



For the early segmentations, then, there are numerical data at 

 hand from which the resultant energy change can be computed in 

 accordance with the "work integral" 



J'»P2 

 V d p 

 Pi 



which becomes, when the volume is constant, 



W =v {p,- p,) 



