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 by 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 
