LOEB. 



309 



sterile sea water. I, therefore, consider it possible that where 

 authors describe a cleavage of the unfertilized sea-urchin eggs 

 in " normal " sea water, that the sea water or the eggs had 

 in reality suffered some change which had escaped the notice 

 of the observers. One might think of evaporation and in- 

 crease in the osmotic pressure of the sea water. A very slight 

 increase in the osmotic pressure of the sea water is sufficient 

 to cause the sea-urchin egg to divide into two cells in the 

 course of twenty hours. One might also think of a change in the 

 sea water brought about by the putrefaction of the dead eggs. 

 Finally it is possible that a substance 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 the prolongation of life 

 upon the other, lead us to the conclusion that a " fertilization " 

 must perhaps come to pass in every egg, even in those naturally 

 parthenogenetic. Only according to our idea, the act of fertiliza- 

 tion is not identical with the morphological 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 condi- 

 tions also, only much too slowly. The difference between 

 naturally parthenogenetic eggs and the eggs which must be fer- 

 tilized 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 parthenogenetic 

 eggs these substances are formed within the eggs (possibly in 

 conjunction with the processes of maturation). 



The connection between the prolongation of life and fertiliza- ( 

 tion clearly points out that every purely morphological theory of 

 fertilization is incomplete and that a correct theory of this process \ 

 must have a physco-chemical basis. The means of reaching this 

 basis I see in further attempts at causing development of unfer- 

 tilized eggs through unequivocal physical and chemical means. 



