THE FERTILIZATION-REACTION 



success, fertilized normally and gave normal development. 

 Comparable results were obtained with eggs of Platynereis; 

 never did I observe copulation of the animals and the con- 

 sequent laying of fertilized eggs before full-moon. 



Often during the early days of its breeding season, the 

 sea-urchin, Arbacia, contains eggs with polar bodies 

 attached, a condition which indicates that maturation was 

 only then ending; usually, normally shed eggs show no polar 

 bodies. Such eggs with polar bodies either are not fertiliz- 

 able at all or only in small numbers. During one season 

 I followed the development of the ovaries of this sea-urchin 

 daily beginning in April through to the first of-^July. Only 

 after the eggs had passed the maturation-stages which 

 occupy a brief period, are they fertilizable. 



The fertilizable condition hangs upon or comes with a 

 change which occupies a mere point of time in the egg's 

 history: before it the egg is unfertilizable and after, fertiliz- 

 able. This is doubtless true also for eggs like Otomesostoma, 

 Dnwphilus, Saccocirrus. The spermatozoa enter these 

 eggs when they are very young ovocytes, i.e., before the 

 eggs' growth-stage. Only when these eggs are fully grown 

 and matured, which state they attain some time after the 

 precocious sperm-entry, can these eggs be said to be fer- 

 tilized. Presumably here also something happens in the 

 egg so that it passes from the condition of unfertilizability 

 to that of fertilizability. 



The fertilizable condition may endure for hours or even 

 for three days as in eggs of sea-urchins, depending upon 

 the species and for any given species upon the temperature; 

 it persists longer at lower than at higher temperatures. In 

 eggs of the flat sea-urchin, Echinarachnius^ its duration is 

 very short compared with that of Arhacia at the same 

 temperature.^ Eggs of other animals, fertilized outside 



^ By frequently changing the sea-water of the same temperature 

 in which the eggs lie, the duration of the fertilizable condition becomes 

 shorter. 



187 



