NaturaL Datu AND FERTILIZATION 745 
stance is perhaps formed (for example, an acid) in the dying 
eggs which brings about a single cleavage. 
The relations which exist between maturation and natural 
death upon the one hand, and fertilization and prolongation 
of life upon the other, lead us to the conclusion that a “fer- 
tilization” must perhaps come to pass in every egg, even in 
those naturally parthenogenetic. Only, according to our 
idea, the act of fertilization is not identical with the mor- 
phological process which is designated fertilization. It is 
rather a chemical or a physico-chemical act which accelerates 
certain (synthetical?) metabolic changes in the egg, which 
occur in the egg under ordinary conditions also, only much 
too slowly, The difference between naturally partheno- 
genetic eggs and the eggs which must be fertilized before 
they can develop consists perhaps in this, that to the latter 
the catalytically working substance or complexus of condi- 
tions must be added from the outside in order to accelerate 
the synthetical (?) processes, while in the naturally partheno- 
genetic eggs these substances are formed within the eggs 
(possibly in conjunction with the processes of maturation). 
The connection between the prolongation of life and fer- 
tilization clearly points out that every purely morphological 
theory of fertilization is incomplete and that a correct theory 
of this process must have a physico-chemical basis. The 
means of reaching this basis I see in further attempts at 
causing development of unfertilized eggs through unequiv- 
ocal physical and chemical means. 
VII. CONCLUSIONS 
1. Our observations and experiments seem to show that 
in the same sea-water and under otherwise identical con- 
ditions, mature but unfertilized starfish eggs soon die, while 
immature as well as mature but fertilized eggs live longer. 
2. It seems certain that the rapid death of the mature 
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