NATURAL DEATH AND FERTILIZATION 729 



a very large plainly visible nucleus. 1 The process of matura- 

 tion consists morphologically in this, that the nucleus 

 becomes invisible and the polar bodies are thrown out. 



This process is completed within one or two hours after 

 the eggs are removed from the ovaries and placed in sea- 

 water. Only when maturation is complete is it possible to 

 cause the egg to develop through the addition of sperm or 

 through the physical and chemical agencies that have been 

 described by me, Delage, Mathews, and Greeley. 



II. THE NATURAL DEATH OF THE MATURE UNFERTILIZED 

 STARFISH EGGS 



The living eggs of Asterias are light yellow in color and 

 homogeneous. They retain this appearance during the pro- 

 cess of maturation as long as they are alive. They retain 

 this appearance also when they are made to develop through 

 the entrance of a spermatozoon or through the proper 

 chemical or physical means. 



If, however, the mature eggs are not fertilized or do not 

 develop, they die in the course of four to twelve hours, and 

 this process of dying is accompanied by a characteristic 

 change in the color of the egg. The egg becomes at first 

 opaque, then almost black, and the homogeneous structure of 

 the protoplasm becomes granular. If such a culture of 

 unfertilized eggs is examined under the microscope after 

 twenty-four hours, two kinds of eggs are found, first, the 

 just-described dark, dead eggs which are mature, and 

 secondly, living, normally colored, but immature, eggs. For 

 usually not all the eggs that are removed from the ovaries of 

 a starfish mature at once ; many mature very late, others not 

 at all. It is readily seen that the immature eggs remain 



i The recent beautiful experiments of Delage have shown that, besides these 

 visible changes in the nucleus, chemical, but morphologically invisible, changes also 

 occur in the protoplasm. DELAGE, "Eludes experimentales sur la maturation 

 cytoplasmique et sur la parth6nogenese artificielle chez les E\;hinodermes," Arch, de 

 zoologie experiment., Vol. IX (1901). 



