NATURAL DEATH AND FERTILIZATION 743 



formed in the parthenogenetic animals which favors the 

 processes of development. We know that an exceedingly 

 small amount of hydrogen ions suffices to bring about devel- 

 opment in unfertilized starfish eggs; that an exceedingly 

 small amount of calcium causes the unfertilized eggs of 

 Amphitrite to develop; and that a trace of potassium ions 

 brings about the development of unfertilized Chsetopterus 

 eggs. 1 It is entirely possible that the specific ions or other 

 substances necessary to start the development of the eggs of 

 the bee are formed within the egg itself through the chemi- 

 cal changes taking place during or after maturation, and 

 that without the formation of these substances develop- 

 ment is impossible. In the case of sea-urchins and starfish 

 eggs one might also believe that the processes of maturation 

 and the processes of development pass over into each other. 

 For it has often been observed that the unfertilized eggs of 

 these forms after having resided in "normal" sea- water for 

 about twenty-four hours begin to cleave shortly before death. 

 This cleavage, however, never goes beyond the two- or four- 

 celled stage. This might be explained by the fact that the 

 eggs begin to die at this time. After I had found this year 

 that the esgs of sea-urchins can still be fertilized after a 



oo 



residence of five days in sterilized sea-water (at summer tem- 

 perature), I decided to study this question of spontaneous 

 cleavage somewhat more closely. If it were true that indi- 

 vidual sea-urchin eggs begin to cleave in ordinary sea-water 

 after about twenty hours, and cease to develop any further 

 only because they soon die, it would be expected that many or 

 all should cleave when kept alive four or five days, and that 

 a number of them should reach a fairly advanced stage of 

 development. A lot of sea-urchin eggs were distributed 

 into a series of flasks containing sterile sea-water. One of 

 the flasks was opened every morning and a careful search 

 was made for developed eggs. 



'LOEB, FISCHER, AND NEILSON, foe. cit, 



