288 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



membrane formation, from the threatening disintegration. Yet 

 this conclusion would be wrong. 



The unfertilized mature egg of S. purpuratus (in which no 

 membrane formation has been called forth) lives at room tem- 

 perature about two or three days and then disintegrates. We 

 saw in a previous chapter that the application of the second 

 factor (the treatment of the egg with the hypertonic solution) 

 may precede the artificial membrane formation by one or more 

 days. If this second factor alone possessed the life-saving action, 

 we should expect that unfertilized eggs treated with the hyper- 

 tonic solution alone would live longer than the unfertilized eggs 

 not treated at all. This is, however, not the case. The unferti- 

 lized eggs of S. purpuratus treated with the hypertonic solution 

 alone die as quickly as the non-treated eggs. The same eggs, 

 however, will live and develop if the membrane formation is 

 called forth. In this case we might say that the membrane 

 formation has the life-saving effect. In reality it is the com- 

 bined action of both b}^ which the life of the egg is prolonged. 



These facts also make it plain why the act of membrane 

 formation alone can save the life of certain starfish eggs or 

 the eggs of certain annelids for which membrane formation 

 alone suffices to induce normal development. Not all the 

 eggs of such animals, e.g., Asterina, are able to develop through 

 artificial membrane formation alone, but only a small number; 

 and we have reason to assume that in these eggs the second 

 factor is formed or pre-exists in ample quantity. For these 

 eggs the mere act of membrane formation is sufficient to save 

 their lives, since they are supposed to supply the second factor 

 themselves. 



It is therefore the causation of development and not the 

 action of one of the two factors alone which saves the life of 

 the unfertilized egg. 



3. We have mentioned the fact that lack of oxygen or the 

 suppression of oxidations prolongs the life of the unfertilized 



