ACTIVATION OF UNFERTILIZED STARFISH EGGS. 303 



branes, but the eggs fail to cleave and soon break down without 

 development; in order to induce favorable development an 

 exposure of three to four times the minimum for membrane- 

 formation is required {e. g., 7-8 minutes at 32°) ; more prolonged 

 exposures are again followed by failure to develop. 



2. Between 29° and 38° the times of exposure required to 

 produce these effects decrease very rapidly with rise of tempera- 

 ture; on the average a rise of i° approximately halves the 

 exposure required for a given physiological effect (such as 

 membrane-formation, or complete activation, or heat-inactiva- 

 tion). The activation-process thus exhibits a characteristically 

 high temperature-coefficient (Oio = 200-400). 



3. The effects of exposure to weak butyric acid solution (w/260) 

 vary with time of exposure in a similar manner, — brief exposure 

 causing membrane-formation followed by breakdown, longer 

 exposures causing cleavage and development to larval stages, 

 and still longer exposures causing cytolysis without development. 



4. The inference is that the same process is initiated in the 

 egg by exposure to warm sea-water as by fatty acid solution. 

 This process must proceed to a certain stage in order that 

 activation may be complete ; if arrested too soon (brief exposure) 

 only partial activation (membrane-formation followed by break- 

 down) results. 



5. Eggs in which membranes are formed by minimal exposure 

 to warm sea- water or w/260 butyric acid, followed by return to 

 sea-water, may be made to develop favorably by a second 

 treatment with either warm sea-water or fatty acid solution, as 

 well as by after-treatment with cyanide-containing or hypertonic 

 sea-water. A favorable after-treatment may thus be of the 

 same kind as the membrane-forming treatment. 



6. The temperature-coefficient of activation by high tempera- 

 tures is of the same order as that of the melting of gels or the 

 decrease in the viscosity of gelatine solutions. The above high 

 temperatures thus probably act by producing degelation-effects 

 in the surface layer of the egg; increase of permeability, with 

 consequent depolarization, is the result of this change. 



7. A new hypothesis of the mode of action of hypertonic 

 sea-water is put forward. 



