706 



SCIENCE 



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



always hold in the egg cell, where as a rule 

 immediately after fertilization a series of 

 cell divisions follow without any increase 

 of mass of the egg. The egg, when divided 

 into two or more cells, does, as a rule, not 

 weigh more (and may possibly weigh a 

 little less) than the original egg cell before 

 it began to divide. This exception from the 

 rule that cell division is preceded by growth 

 of the cell is not real, since the egg cell is at 

 first much larger than the ordinary body 

 cell of the growing organism. If the rela- 

 tion between size of cell and cell division 

 exists we must expect that the egg cell after 

 it is fertilized must first undergo a series 

 of cell divisions without any growth, until 

 each cell of the original egg has been re- 

 duced to the size of the cell characteristic 

 for the species. Only after this has hap- 

 pened can the ordinary cycle of growth of 

 the cell with subsequent cell division begin. 



The writer is suspicious that even in eggs 

 where we notice at first cell division with- 

 out growth, in reality growth may take 

 place. Such eggs as those of the sea urchin 

 consist largely of reserve material which is 

 gradually transformed into the peculiar 

 state which we designate as living proto- 

 plasm (and which may differ from non- 

 protoplasmic material in the possession of 

 synthesizing enzymes or mechanisms). In 

 the first stages of cell division this transfor- 

 mation of reserve material into living ma- 

 terial may occur, and this transformation 

 is the real growth which we observe in the 

 bacteria and later on in the cells of meta- 

 zoa, but which is not directly visible in the 

 first stages of cell division in the egg. 



The unfertilized egg immediately before 

 fertilization is usually unable to divide 

 even under the most perfect conditions. 

 "With all the food existing in a hen's egg 

 the germ can not grow unless it is fertilized, 

 while this growth takes place after a 

 spermatozoon has entered the egg. There 

 exists, therefore, a mechanism by which the 



same egg cell can be in a state of rest in 

 which growth is inhibited. "Wliat is the 

 nature of this peculiar inhibitory mechan- 

 ism and what is the mechanism by which 

 the entrance of a spermatozoon abolishes 

 this inhibition? The experiments on arti- 

 ficial parthenogenesis^ allow us to give a 

 partial answer to this question. 



In the case of certain eggs, e. g., the egg 

 of the sea urchin, the entrance of a sperma- 

 tozoon is followed immediately by a strik- 

 ing change in the surface of the egg. The 

 latter surrounds itself with the so-called 

 fertilization membrane. If we induce this 

 membrane formation by certain chemicals 

 (e. g., a short treatment with a fatty acid) 

 the eggs when put back into normal sea 

 water will begin to develop at a low tem- 

 perature and may reach the larval stage. 

 But at the temperature of the room or 

 even of the ocean the eggs may begin to 

 develop, but they will perish the more 

 rapidly the higher the temperature. On 

 the other hand, the eggs if fertilized with 

 sperm will develop at room temperature. 

 What causes this difference? The answer 

 is that the alteration of the surface of the 

 egg induced by a fatty acid initiates devel- 

 opment but is not sufficient to guarantee a 

 normal development at ordinary conditions. 

 For this purpose a second treatment is re- 

 quired and this can be given in the form 

 of a short treatment with a hypertonic 

 solution or a longer treatment with lack of 

 oxygen. After the egg has received the 

 second treatment it can develop into a 

 normal larva at room temperature. I am 

 suspicious that even a third factor may 

 have to be supplied, since the mortality of 

 the parthenogenetic larvae is greater than 

 that of the normally fertilized eggs. 



"Why is it that the membrane formation, 

 or more correctly an alteration of the sur- 



5 The reader is referred to the writer's book on 

 "Artificial Parthenogenesis and Fertilization," 

 Chicago, 1913, for details and literature. 



