296 LOEB. 



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 Astcrias are light yellow in color and homo- 

 geneous. They retain this appearance during the process of 

 maturation as long as they are alive. They retain this appearance 

 also when they are made to develop through the entrance of a 

 spermatazoon or through the proper chemical or physical means. 



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

 develop, they diej.n 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 opaxme, then almost 

 black, 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 maturate at once ; many maturate very late, others 

 not at all. It is readily seen that flic immature eggs remain alive 

 fur several da\s until they finally become the prey of bacteria; 

 , while the mature eggs become opaque and die in four to twelve 

 hours after maturation has been completed. 



Is the death of the mature but undeveloped egg brought about 

 through internal conditions or through the bacteria contained in 

 the sea water? 



A trustworthy way of determining this consists in making 

 sterile culture of the eggs in sea water. This is a relatively simple 

 procedure in the case of starfish. Eight flasks were sterilized, 

 filled with sterilized sea water, and again heated for twenty 



