42 4, F, KEIBEL. 
ing and discussing the preparations have no direct connection 
with the chief question concerning the definition of gastrula- 
tion and the interpretation of the primitive streak in Am- 
niota. They will be solved in the course of time by special 
researches, some of them of a more complicated nature. 
Here I only wanted to express, and to establish to a certain 
extent, that it would be well to follow Hubrecht in the defini- 
tion of gastrulation and that we should introduce certain 
corresponding alterations in our nomenclature. 
