Artijlciol Parthenogenesis tn Starfish Eggs 385 



seconds; at 37.5° between 5 and 15 seconds, and at 40° momen- 

 tary exposure (5 seconds) produces membranes in practically all 

 eggs. These temperature-relations point to an underlying process 

 that undergoes unusually rapid acceleration with rise of tempera- 

 ture, until a certain optimum is reached (apparently in the neigh- 

 borhood of 40°), after which heat acts unfavorably. Exposure 

 to 45° for 30 seconds fails, as seen above, to produce membranes 

 and acts destructively on the eggs, although briefer exposure (15 

 seconds) may be effective. 



The actual separation of the membrane may be readily studied. 

 Within 10 to 15 minutes after return to normal sea-water it appears 

 as a wavy or crenated layer adhering closely to the egg-surface; 

 this layer gradually detaches itself as the sea-water enters the space 

 next the cell-surface, and with the resulting distension the inequal- 

 ities disappear; after 20 to 25 minutes (at 20° to 22°) the membrane 

 is uniform and normal in appearance, though still very near the 

 egg-surface. The process may be characterized as secretory in 

 nature, and it appears to be dependent on a partial solution of the 

 superficial lipoid layer of the egg; this is indicated by its ready 

 production through the action of the various fatty acids and fat- 

 solvents. The above temperature-relations appear to indicate, 

 in the case of production by warming, a dependence on some 

 enzyme action. If a simple solution of certain substances at higher 

 temperatures were the determining condition, the high tempera- 

 ture-coefficient of acceleration, as well as the failure of tempera- 

 tures above 45° so to act, would be unintelligible. On the other 

 hand, the assumption of dependence on some process accelerated 

 by an enzyme with an optimum temperature of 38° to 40°, and 

 rapidly destroyed at 45°, would account for the above relations. 

 Certain hydrolytic cleavages may be concerned, possibly a saponi- 

 fication resulting in a partial solution of the surface layer; the 

 production of the same effect by the action of fat-solvents or alkalis 

 becomes readily intelligible on such an assumption. 



An important significance has been ascribed by Loeb to the 

 process of membrane-production in sea-urchin eggs. After mem- 

 brane-formation, however induced, the condition of the egg is 

 altered in such a manner that relatively brief exposure to hyper- 



