708 



SCIENCE 



[N. S. Vol. XLI. No. 1063 



develop before they leave the ovary. This 

 is not the case. 



The work on physiologically balanced 

 salt solutions has brought out the fact that 

 the permeability of the cells in a body may 

 undergo variations and when this happens 

 it is conceivable that the lysins in the blood 

 may induce eggs to develop in the ovary. 

 Leo Loeb states that 10 per cent, of the 

 eggs in the ovary of a guinea-pig may show 

 a beginning of parthenogenetic develop- 

 ment, and certain spontaneous tumor for- 

 mations in the human ovary may find their 

 explanation in this way. In other words, 

 it is not excluded that one form of limited 

 growth may be due to the immunity or im- 

 permeability of cells to blood of the same 

 species. 



The question then why an unfertilized 

 egg can not grow and why a fertilized egg 

 possesses the power of dividing and grow- 

 ing is therefore answered in the sense that 

 both conditions depend apparently upon 

 the condition of the surface layer of the 

 cell. 



The most important fact for our present 

 problem is the observation that the altera- 

 tion which starts the development of the 

 egg is to some extent reversible. The his- 

 tory of the egg is such that after a num- 

 ber of cell divisions the final stage of the 

 unfertilized egg ready for fertilization is 

 reached. If at that stage it is fertilized by 

 sperm or induced to develop by artificial 

 means the processes of cell division and 

 growth will continue; if not, the egg will 

 soon die. There is a third possibility. The 

 unfertilized egg may start to develop, then 

 stop and go practically, though not entirely, 

 back into the state in which it was before 

 starting to develop. 



The clearest case of this kind was ob- 

 served in the egg of the Califomian sea 

 urchin. When the unfertilized egg of 

 Strongylocentrotus purpuratv^ is treated 



with a hypertonic solution the eggs may 

 begin to segment into two, four, or eight 

 or sixteen cells, but then they cease devel- 

 oping and go back into the resting condi- 

 tion in which they were before the egg 

 started dividing, with the exception of one 

 condition which will be mentioned later. 

 In the place of each of the original eggs 

 we have now two, four, eight, etc., smaller 

 cells. The observation is of importance for 

 the theory of fertilization, because it dis- 

 poses of the idea once held by Boveri that 

 eggs are in the resting stage because they 

 are lacking the apparatus for cell division; 

 these eggs went into the resting stage again 

 in spite of the fact that they possessed the 

 apparatus for normal cell division. If the 

 cells of such an egg are at a later time fer- 

 tilized with sperm, they form a fertiliza- 

 tion membrane and develop. They will 

 develop also into larva if they only re- 

 ceive the butyric-acid treatment without 

 the corrective factor. The original treat- 

 ment with the hypertonic solution provided 

 these eggs permanently with the corrective 

 effect. 



What caused these eggs which were seg- 

 menting to go back into the resting stage? 

 I am inclined to assume that in these eggs 

 the change in the cortical layer which 

 started the development was gradually or 

 suddenly reversed. We should expect this 

 to betray itself in a lowering of the rate of 

 oxidations. Wasteneys and I have found 

 indeed that unfertilized eggs of purpuratus, 

 which show an increase in the rate of oxida- 

 tions after a treatment with a hypertonic 

 solution, show a lower rate if examined 

 after some time. It seems then possible 

 that the change in the cortical layer which 

 leads to a rise in the rate of oxidations is 

 under certain conditions reversible. 



These are not the only cases of rever- 

 sion. I noticed that if the development of 

 the eggs of Ariacia is induced either by a 



