116 The Mechanistic Conception of Life 



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are those on parthenogenesis. It had been observed for a 

 long time that the unfertilized egg of the silkworm can develop 

 parthenogenetically. It was, moreover, known that plant lice 

 can give rise to new generations without fertilization. The 

 most impressive fact concerning the parthenogenesis of animals 

 was contributed by Dzierzon, who discovered that the unferti- 

 lized eggs of bees develop and give rise to males, while the 

 fertilized eggs give rise to females. Similar conditions seem to 

 exist in wasps. It is, moreover, certain that a few crustaceans 

 show parthenogenesis. 



A beginning of parthenogenetic development had been 

 observed in the case of a great many marine animals which 

 develop outside of the female in sea- water. It was found that 

 such eggs when left long enough in sea-water may divide into 

 two or three cells, but no farther. On the other hand, in 

 ovaries of mammals now and then eggs were found that were 

 segmented into a small number of cells. ^ These facts and the 

 occurrence of a certain class of tumors in the ovary, the so-called 

 teratomata, suggest the possibility of at least partial partheno- 

 genesis in the eggs of mammals. But all these phenomena 

 were considered to be of a pathological character. It must be, 

 however, admitted that we cannot utilize these facts with any 

 degree of certainty for the theory of fertilization, as in this 

 case certainty can only be obtained by the experiment. It 

 was not until very recently that such experiments were made. 



II 



Eight years ago I observed that if the fertilized eggs of the 

 sea-urchin were put into sea-water Avhose concentration was 

 raised by the addition of some neutral salt they were not able 

 to segment, but that the same eggs, when put back after they 

 had been in such sea-water for about two hours, broke up into 

 a large number of cells at once instead of dividing successively 



1 Hertwig, O., Die Zelle und die Gewebe, p. 239, Jena, 1893. 



