DURATION OF EMBRYO DEVELOPMENT. 39 



In all the eggs the germinal vesicle had disappeared, 

 and in the living egg. which was but slightly trans- 

 parent, I could see nothing at all left of it. In one 

 place, namely, the upper pole of the egg, there was to 

 be seen on the surface a tolerably clear mass of pro- 

 toplasm poorly supplied with yolk, and on the surface 

 of this a clear and already quite sharply defined polar 

 body. As I found the polar body already fully defined 

 a short time (perhaps a quarter of an hour) after the 

 ejection of the eggs, I think I must conclude that 

 already, during the course of the day, isolation of the 

 individual eggs from one another and the ejection of 

 the polar body took place within the atrial cavity. 



I could now understand why the artificial fertiliza- 

 tion, which had been so often tried, never would 

 succeed. The reason is that the eggs, which were ob- 

 tained by pulling the ovaries to pieces, could never be 

 completely isolated from one another, and always ex- 

 hibited a large distinct germinal vesicle with germinal 

 spot and nucleolus. They were not therefore in a 

 condition capable of fertilization, since, as we see, in 

 the Amphioxus the fertilization does not take place till 

 after the ejection of the polar body, that is, a con- 

 siderable time after the expulsion from the ovaries. 



