298 RALPH S. LILLIE. 



Hence it is a matter of secondary importance in what manner 

 this semi-permeabiHty is temporarily destroyed, provided that 

 the condition of increased permeabiHty lasts long enough — not 

 too long — and is not associated with irreversible changes making 

 recovery impossible. It is presumably during this stage of 

 increased permeability that the above specific interaction takes 

 place; this process requires time, and its rate will be a function 

 of the rate at which the two interacting substances can come 

 together; this second rate will be a function of the viscosity 

 or gelation-state of the protoplasmic system at the site of inter- 

 action,^ — hence its dependence on temperature, as seen above. 

 When this critical interaction has taken place, there follows at 

 once the characteristic change of physiological activity normally 

 resulting from fertilization; membrane-formation and the other 

 events preparatory to cell-division occur and the developmental 

 process proper is initiated. How far development proceeds, 

 however, depends on the degree of completion of the primary 

 specific reaction; hence for complete activation the exposure to 

 the membrane-forming condition must have a certain minimal 

 duration, and in case the preliminary exposure is insufficient 

 some after-treatment may be necessary to complete the process. 

 This after-treatment may be of the same kind as the preliminary 

 membrane-forming treatment, or it may be of entirely different 

 kind — -e. g., hypertonic sea-water, cyanide, an anaesthetic, etc. 

 But there seems to be no need of assuming that its direct physio- 

 logical effect is qualitatively different from that of the membrane- 

 forming agent. ^ It merely renews and brings to completion a 

 process already initiated by the first treatment. 



Comparative study of the conditions of both normal and 



1 The above experiments are a sufficient justification of this contention. But 

 they do not explain why, for instance, after-treatment with cyanide, which by itself 

 does not induce membrane-formation in starfish eggs (cf. Journal of Experimental 

 Zoology, 1913, Vol. 15, p. 38), is so effective. Clearly the condition of the egg after 

 membrane-formation is altered so that the activation-process may then be influ- 

 enced by agents which previously had no effect upon it (as cyanide, alcohols, or 

 hypertonic sea- water in brief exposure). Sensitization to these agents seems to be 

 involved in the process of membrane-formation, but the basis of this effect can not 

 be defined at present. There is, however, no necessary inconsistency between these 

 facts and the conception that the activation-process is essentially unitary in char- 

 acter in the above sense. The case of hypertonic sea-water offers certain special 

 problems, which are partly discussed below. 



