THE FERTILIZATION-PROCESS 



worms. Fertilization of eggs whose nuclei are hindered 

 from taking part in development has been accomplished on 

 eggs of sea-urchins and of amphibia. Experimentally it is 

 thus shown that neither fusion nor even mere apposition of 

 the sperm- with the egg-nucleus is essential for the fertiliza- 

 tion-process. 



Some observations of my own bear on this point. The 

 first of these shows that in eggs of Echinarachnius, fertilized 

 after having been treated with dilute sea-water — or after 

 having lain in sea-water for several hours — the egg-nucleus 

 takes no part in the subsequent cleavages but remains as a 

 "resting nucleus" in every way similar to its condition in 

 the unfertilized egg.^ In the meantime, the sperm-nucleus 

 divides in the typical manner of the zygote-nucleus. The 

 second observation relates to eggs of the sea-urchin, Arbacia, 

 fertilized In various stages of mitosis Induced by treatment 

 with hypertonic sea-water.^ In some of these eggs the 

 egg- and sperm-nuclei divide independently though in dif- 

 ferent tempo, as one would expect. Here then the stage 

 in the mitotic activity of the egg-nucleus does not inhibit 

 the independent activity of the sperm-nucleus. 



The evidence derived from observations on normal fer- 

 tilization-processes indicates that fertilization can occur 

 without fusion, union, apposition, or even approach of 

 the sperm- and egg-nuclei. The experiments cited show 

 that development ensues when the egg-nucleus is absent or 

 when though present it is rendered inert. We are therefore 

 not justified In retaining the old definition of fertilization 

 as fusion of the egg- and sperm-nuclei. 



To speak of the RJiabciitis-egg, for which sperm-penetra- 

 tion is essential to development, as "nature's bridge 

 between parthenogenesis and fertilization,"''^ because the 



1 Just, I()24. 

 ' Just, I<)22h. 

 ^ Bracket, 191 J. 



181 



