2 50 PROBLEMS OF FERTILIZATION 



the membrane-formation at 30° as at 35°; the ratios between 

 29° and 34° and between 31° and 36° are the same. At each 

 temperature the proportionate durations of the minimum, 

 optimum, and maximum exposures for forming larvae are approx- 

 imately the same. In other words the critical change under- 

 lying simple membrane-formation is affected by temperature in 

 the same way as that underlying complete activation of develop- 

 ment: i.e., the proportionate increase in velocity by rise of tem- 

 perature is the same in both cases, a fact which can only indicate 

 that one fundamental process — and not two — is concerned in 

 producing both effects. If we assume that the foregoing propor- 

 tionate increase in velocity prevails through a rise of 10°, a Qio 

 value of from 225 to 400 is indicated, as against the 2 to 3 

 characteristic of chemical reactions in homogeneous media. 

 Activation by heat thus depends on some critical change in the 

 egg which does not begin until a temperature of about 29° is 

 reached, but which undergoes very rapid acceleration with further 

 rise of temperature. The liquefaction of gels by heat seems to 

 be the only relevant process which shows these characteristics. 

 The change in viscosity preceding the gelation of a gelatine sol 

 undergoes very rapid acceleration with lowering of temperature, 

 within a few degrees of the temperature of gelation. The inverse 

 process, melting of gels, has a similarly high temperature coeffi- 

 cient. In general the facts suggest that the direct effect of the 

 high temperature is to cause a change in the colloidal system of 

 the egg, of such a kind as to render possible a chemical inter- 

 action between substances which in the normal condition of the 

 resting egg are kept apart. This restraining condition may be 

 some physical barrier like a membrane, impermeable to the dif- 

 fusion of the substances concerned, or it may be a certain state 

 of electrical polarization of the general cell-surface. 



Two other important facts in the experiments of 

 this author should also be stated: (i) It is possible 

 to arrest the progress of the activation process by 

 returning the eggs to sea-water at normal temperature, 

 and to cause a renewal later by restoring the tempera- 



