REJUVENESCENCE IN EMBRYO AND LARVA 405 



differentiated, physiologically old cells, approaching death, an 

 increase in dynamic activity can scarcely mean anything else than 

 the beginning of a period of rejuvenescence and dedifferentiation. 

 The increase in the dynamic activity of the sea-urchin egg after 

 fertilization has been determined in various ways by various inves- 

 tigators. 1 Lyon found that the susceptibility of the eggs to cyanide 

 was greater after than before fertilization. Measurements of the 

 oxygen consumption of the egg of the Neapolitan sea-urchin 

 (Strongylocentrotus limdus) by Warburg showed that after fertiliza- 

 tion the oxygen consumption was between six and seven times as 

 great as before, and Loeb and Wasteneys found that in an American 

 sea-urchin (Arbacia punctulata) the fertilized egg consumed three 

 to four times as much oxygen as the unfertilized. 2 In a study of 

 heat production in the sea-urchin egg Meyerhof finds the heat 

 production per hour between four and five times as great in fer- 

 tilized as in unfertilized eggs. 



In the starfish egg, however, according to Loeb and Wasteneys 

 ('12), the oxygen consumption is about the same before and after 

 fertilization. This difference in behavior between starfish and sea- 

 urchin eggs is undoubtedly connected, as Loeb ('n) suggested, 

 with the fact that in the starfish the extrusion of the eggs from the 

 ovaries into sea-water starts the maturation divisions, while in the 

 sea-urchin maturation has occurred and the egg is quiescent when 

 the sperm enters it. But the unfertilized starfish egg dies very 

 soon unless, according to Loeb, its oxidation processes are inhibited 

 by lack of oxygen or by cyanide. 3 As a matter of fact, the starfish 

 egg is almost a parthenogenic egg, as Mathews ('01) has shown. 

 By experimental means its development can readily be initiated 

 without fertilization. But, left to itself, it is apparently not quite 

 able to begin normal development; something goes wrong and 

 death soon follows. The unfertilized sea-urchin egg, on the other 

 hand, which remains almost quiescent after extrusion from the 



x Loeb, '10; Loeb and Wasteneys, '10, 'n; Lyon, '02; Meyerhof, 'n; Warburg, 

 '08, '10. 



2 There are certain sources of error in the method used for determining oxygen 

 ( onsumption which make it possible that these values are too high, but that an increase 

 ( ccurs cannot be doubted. 



3 Loeb, 'n; Loeb and Wasteneys, '12. 



